Showing papers by "Paul Sabatier University published in 1975"

A theoretical method to determine atomic pseudopotentials for electronic structure calculations of molecules and solids

Abstract: The characteristic features of model potentials, effective potentials and pseudopotentials are carefully investigated. Then we justify our choice to work only with hermitian pseudopotential operators, and we develop a general non-empirical method to determine atomic pseudopotentials. In view of their numerical use for molecular calculations, these pseudopotentials are cast into semi-local forms, and their parameters are obtained by a least-squares process; tables of parameter values are given for the two first rows of the periodic system.

Delocalized and localized pictures of excited and ionized states

Abstract: The valence shell repolarization under a core ionization in a diatomic molecule as N2 is analyzed through localized and delocalized pictures, showing their total equivalence. The interpretation is easier in the localized model, appearing mainly through local single excitation processes; in the delocalized model the repolarization effect is hidden (partly or totally) under double excitation processes involving simultaneous excitations in the valence shell and hole change in the core level, appearing therefore as a “correlation effect”. This effect is analyzed forn Be atoms, showing an −1 behaviour of the single excitations effect in the delocalized model, and explains the Hartree-Fock unstability numerically verified on O 2 + , but it prevents to give any physical meaning to the “localization of the core hole in a diatomic molecule”.

Dielectric and depolarization thermocurrent study of the γ relaxation in polyethylene isophthalamide

Abstract: The depolarization thermocurrents (DTC) from polyethylene isophthalamide are studied below the glass-transition temperature The “entire” DTC spectrum is analyzed in terms of a continuous distribution of relaxation times; the corresponding distribution function is very close to that which fits data deduced from bridge measurements The complex DTC spectrum can be experimentally resolved into single relaxation time processes The analysis of each “elementary” DTC peak yields dielectric dispersion and relaxation time which allow one to calculate the frequency variation of the complex dielectric constant The corresponding Cole–Cole plot is in good agreement with that deduced from studies of the “unresolved” γ relaxation

Determination of the electron excitation spectrum in scandium and yttrium by means of characteristic energy loss measurements

Abstract: Energy loss spectra of high energy electrons transmitted through thin foils of scandium and yttrium have been registered using two different experimental techniques. A detailed comparison of the results allows to distinguish between the spectra of metals, hydrides, and oxides and to calculate the optical constants in the pure metals. It is shown that the electron excitation spectra of these elements contain two main contributions in the energy range between 5 and 60 eV: collective excitations of the conduction electrons at 14 and 12 eV (plasmon peaks) and a strong absorption band due to the excitation of the inner 3p and 4p electrons between 30 and 50 eV. At higher energies, these spectra display well-defined lines corresponding to the L2−3 edge in scandium and to the M4−5 and M2−3 edges in yttrium which are characteristic of the atom. Les spectres de pertes d'energie d'electrons de haute energie transmis a travers des films minces de Scandium et d'Yttrium ont ete enregistres a l'aide de deux techniques differentes. Une comparaison detaillee des resultats a permis de distinguer les spectres du metal, de l'hydrure et de l'oxyde, et de calculer les constantes optiques pour le metal pur. On montre ainsi que le spectre des excitations electroniques de ces elements contient deux contributions principales dans le domaine d'energie compris entre 5 et 60 eV: l'excitation collective du gaz d'electrons de conduction a 14 et 12 eV respectivement (pics de plasmons) et entre 30 et 50 eV une bande d'absorption intense due a l'excitation des electrons 3p et 4p. A plus forte energie, ces spectres contiennent des lignes bien definies correspondant au seuil L2−3 du Scandium, et aux seuils M4−5 et M2−3 de l'Yttrium, qui sont caracteristiques de l'atome.

Dynamique des populations et production du zooplancton du lac de Port-Bielh (Pyrénées centrales)

Abstract: Trois Crustaces et quatre Rotiferes composent le zooplancton du lac de Port-Bielh (2 285 m) ou dominent Mixodiaptomus laciniatus et Daphnia longispina.La distribution verticale des organismes et ses variations nycthemerales different selon les especes et, pour une meme espece, selon les stades de developpement. La quantite d'animaux exportes en 24 h par le deversoir, liee a la distribution verticale du zooplancton, represente un faible pourcentage des populations (0,14 a 2,8 ‰) mais une biomasse importante (0,45 a 1,2 kg PF/jour).Le cycle de developpement des Crustaces se caracterise par une longue phase de repos durant les 7 mois de gel, une courte periode de reproduction au debut de l'ete et une phase de croissance rapide (aout et septembre) aboutissant a une biomasse maximale en octobre. La duree de developpement des differents stades de M. laciniatus et de D. longispina, determinee d'apres l'evolution numerique des populations, est proche des durees obtenues experimentalement par plusieurs auteurs.La production de M. laciniatus et de D. longispina a ete calculee a partir de l'evolution du poids des individus en fonction de leur âge et de la variation du poids moyen des organismes au cours de l'ete. Ces deux methodes et leur variante graphique donnent des resultats assez voisins. Le rapport Production/Biomasse maximale est comparable pour les deux especes (1,35 a 1,65) et se situe dans les valeurs deja mentionnees pour des populations d'insectes aquatiques d'altitude. La production du Rotifere dominant (Polyartra vulgaris) represente moins de 1 % de celle des deux Crustaces.La comparaison de la production primaire et secondaire de la zone pelagique indique une exploitation intense du phytoplancton par les herbivores. Malgre une faible biomasse, les algues constituent vraisemblablement une source de nourriture suffisante pour assurer la production du zooplancton.

Arterio-venous transfer of testosterone in the spermatic cord of man.

Abstract: A counter-current exchange mechanism for testosterone has been demonstrated between venous and arterial blood in the spermatic cord of man.

Cycle biologique et production de Capnioneura brachyptera D. (Plécoptères) dans un ruisseau d'altitude des Pyrénées centrales

Abstract: Le cycle de developpement de Capnioneura brachyptera dure deux ans dans un ruisseau des Pyrenees centrales, a 1 950 metres d'altitude. Le premier hiver est passe a l'etat d'oeuf ; la croissance, tres faible la premiere annee, devient tres rapide au cours du deuxieme ete des la fin de la fonte des neiges. La production varie peu d'une cohorte a la suivante et correspond, pour 70 %, a la croissance de deuxieme annee. La mortalite larvaire parait faible. Le rapport P/B max., compris entre 1,5 et 2 est voisin de ceux deja mentionnes pour d'autres especes des Pyrenees centrales.

Approche hydrodynamique de la microdistribution d'invertébrés benthiques en eau courante

Abstract: La microdistribution des larves et nymphes de 3 especes de simulies (Odagmia variegata, Odagmia obreptans et Simulium rupicolum) a ete observee en divers cours d'eau pyreneens. Ces especes se rencontrent en presence de vitesses importantes qui, dans les ruisseaux etudies, etaient presentes dans les zones a ecoulement torrentiel. Nous ne les avons pas rencontrees dans les zones a ecoulement general de type fluvial. Les pierres lisses et d'un diametre superieur a 10 cm environ sont les substrats les mieux colonises. Les faces amont faiblement inclinees presentent les plus fortes densites larvaires. Dans les zones a fort courant, en presence d'un gradient longitudinal meme reduit des vitesses, les larves se concentrent dans une etroite bande ou les vitesses sont maximales. Le corps des larves est couche vers l'aval et subit les pulsations du courant. Les larves de simulies colonisent rapidement des canaux immerges dans un ruisseau (fig. 2) ; et par suite, les conditions hydrauliques locales peuvent etre precisees aux endroits ou se fixent les larves. En une meme station, le debit variant dans le temps, le type d'ecoulement peut passer du fluvial au torrentiel (fig. 3 et 4). Les profils des vitesses a la paroi, c'est-a-dire dans la zone ou vivent les invertebres, peuvent etre determines en fonction de la rugosite apparente de la paroi (fig. 6). Les conditions d'existence d'un film laminaire (sous couche laminaire) dependent de la vitesse du courant et de la dimension des asperites (fig. 7 et 8). Pour une vitesse de courant donnee, les relations entre l'epaisseur δ du film laminaire et la dimension e des asperites determinent les possibilites d'existence du film laminaire (fig. 8). La variation de l'epaisseur du film laminaire est representee en fonction de la vitesse du courant dans un abaque (fig. 9) qui tient compte egalement des conditions imposees par la dimension des asperites. Le film laminaire n'a qu'une influence reduite sur les conditions de vie des larves de simulies; la turbulence joue un role important sur ces conditions de vie.

Recherches sur l'origine des différentes lign'es de cellules sanguines chez l'Amphibien Urodèle Pleurodeles waltlii

Abstract: Grafting of haemopoietic organs was performed at several developmental stages between diploid and autotetraploid individuals of Pleurodeles waltlii. The difference in size between diploid and tetraploid cells is so obvious that their identification is possible by direct microscopic examination. To avoid immunological rejection, the grafts have been made with inbred animals. 2. After grafting the spleen, the host cells are observed to colonize it. This phenomenon is more important with spleens from donors at early stages of development. When the spleen from a late larval stage or a metamorphosed animal is transplanted into another larva, the blood of the latter contains 66 or 72% erythrocytes originating from the graft. 3. Embryonic liver grafting is followed by a colonization of all haemopoietic organs by cells originating from the granulopoietic tissue of the graft. The proportion of grafted blood cells is then very high. A liver graft performed at a larval stage gives qualitatively similar results but the numbers of cells originating from the graft are lower. A survey of intra-cardiac erythropoiesis in these animals shows that it develops from stream blood cells and not from cardiac endothelial cells. 4. After thymus graft, the lymphoid part of the organ is replaced by the host cells. 5. From these results, it is suggested that the granulopoietic liver tissue contains one or several kinds of stem cells which could differentiate into all types of blood cells.

Fibrations spinorielles et twisteurs généralisés

Abstract: In the first part my purpose is to find existence conditions for a spin structure on a manifold in a purely differential geometric scope, without the machinery of the algebraic topology and avoiding systematically any matricial formalism.

L'Ecologie des arthropodes muscicoles à la lumière de l'Analyse des Correspondances: Collemboles et Oribates du Sidobre (Tarn, France).

Abstract: A statistical method (Benzecri's Factorial Analysis of Correspondances) is used to study the distribution of microarthropods in mosses growing on a forest rock and in surrounding soil. 26 species of Insects (Collembola) and 45 species of Acari (Oribata) were investigated.Comparison of data shows a graduate variation of the population from the soil itself to the aerial mosses, passing by soil mosses.A population gradient is shown from dry and highly drained mosses of south face of the rock to the deep edaphic biotops of the north face. Relative specific affinity for the various samples makes conspicuous their ecologic specialization and the importance of humidity and temperature as distribution factors. A continuous variation of biotops is characterized by a continuous variation of populations.

Réactivité des silyl- et germylphosphines vis-à-vis de divers composés à insaturation CN: imines, α-diimines, N-acylimines et cétènimines

Abstract: Silylphosphines R3SiPR′2 add on the CN group of aldimines yielding phosphinylated silylamines of the structure . Hydrolysis of these adducts leads to the corresponding substituted aminomethyl-phosphines. In the reaction between α-diimines and silylphosphines or silyldiphosphines R2Si(PR′2)2 the acyclic 1/1 and ½ addition compounds have been characterized. The adduct 1/1 obtained by the action of diethyl-hydrodimethylsilyl-phosphine on di-tert-butylimino-ethane undergoes in the presence of Wilkinson's catalyst, (Ph3P)3RhCl, an intramolecular Si-H/CN cyclisation leading to a phosphinylated siladiazolidine. Silylphosphines add to N-acylimines in 1,4 position to form phosphinylated siloxyimines. The methanolysis of the latter derivatives is an novel method of preparation of phosphinylated amides. Silyl- and germylphosphines react on the CN groupement of cetimines. The hydrolysis of the adducts (N-metallated enamines) leads to C-phosphinylated imines.

16-component theory of the spin-1 particle and its generalization to arbitrary spin

Abstract: The criteria of validity of this theory are, among others, the nonrelativistic approximation, the classical approximation which gives the Thomas spin theory, and the values of the energy in a homogeneous magnetic field. In the tensorial form, this theory is more complicated than the 10-component Proca theory, but, in the matrix form, it is more convenient than the preceding theory using the Petiau-Duffin-Kemmer matrices, because only matrices obeying the Dirac conditions intervene. When the mass term is equal to zero ($k=0$) one can recover the Maxwell equations, as a particular case. Finally, the theory may be easily generalized for an arbitrary spin of value $J=\frac{n}{2}$.

Ephéméroptères du Sud-Ouest de la France. I. - Migrations d'imagos à haute altitude

Abstract: Une revue bibliographique des travaux concernant les migrations d'imagos d'insectes aquatiques vers l'amont des cours d'eau est donnee. De telles migrations sont etudiees sur les Ephemeropteres de deux torrents des Pyrenees entre 2 160 et 2 750 m d'altitude. Plus de 800 imagos ♀ de Rhithrogena loyolaea Navas et de Baetis alpinus (Pictet) ont ete recoltees dans l'eau, apres oviposition dans des zones nettement en amont de la limite de presence des larves âgees. Le deplacement des ♀ vers l'amont se fait jusqu'au point de jaillissement de l'eau : source froide ou limite de l'enneigement du torrent, ce qui confirme l'exactitude de l'hypothese du cycle de colonisation de Muller chez les Ephemeropteres de haute montagne. Des gains d'altitude d'un minimum de 170 m (B. alpinus) et de 350 m (R. loyolaea) ont ete observes. L'eclosion peut avoir lieu, chez B. alpinus, dans des eaux dont la temperature est toujours comprise entre 0 et 3 °C.

Influence de la température sur le taux de pulvérisation de cibles de silicium et germanium

Abstract: 2014 Si and Ge single crystal targets were bombarded with high doses of 40 keV Ar+ ions ( > 1017 ions/cm2). The variation of the sputtering yield S as function of the target temperature (50-500°C) has been studied. The measurements of S lead to a determination of the annealing temperature (~ 350 °C for Ge and ~ 400 °C for Si). The sputtering yields of perfect single-crystal Ge targets have been measured. Classification Physics Abstracts 7.180 Tome 10 No 4 Juillet 1975

[Characterization and properties of two dehydroquinate hydro-lyases in higher plants].

Abstract: Two dehydroquinate hydro-lyases (E.C. 4.2.1.10) have been routinely separated from different organs of Zea mays L. by chromatography on Cellex-D Bio-Rad or hydroxypatite using linear salt gradients. Dehydroquinate hydro-lyase 1 is associated with shikimate: NADP+ oxidoreductase (E.C. 1.1.1.25). DHQase 2 is a free constitutive enzyme; in this respect it differs from the inducible enzyme of microorganisms which appears only when dehydroquinate or quinate is the principal carbon source. DHQase 1 and DHQase 2 have a similar apparent Michaelis constant and pH optimum, but they differ in their molecular weight, thermal stability and sensitivity to metabolic effectors. DHQase 2 is specifically activated by shikimic acid. This strong activation and the channeling properties of the complex involved in the shikimate pathway can provide an effective means of control in the utilization of dehydroquinate between two different pathways. The significance of such a system involving both a specific regulation of isoenzymes and a molecular compartmentation by means of an enzymatic complex is discussed.