Showing papers by "Centre national de la recherche scientifique published in 1968"
TL;DR: Mutants that have simultaneously lost feedback inhibition by uridine triphosphate for carbamoyl phosphate synthetase and for aspartic transcarbamylase have been found and mapped in the gene ura-2.
Abstract: Biochemical steps of the pyrimidine pathway have been found to be the same in yeast as in bacteria, and all except one step have been characterized. The activities of the first two enzymes, carbamoyl phosphate synthetase and aspartic transcarbamylase, are simultaneously controlled by feedback inhibition and repression. Moreover, these enzymes are coded by the same genetic region (ura-2) and seem to form a single enzymatic complex. The enzymes that follow later in the pathway are induced in a sequential way by the intermediary products and are insensitive to pyrimidine repression. The corresponding genes (ura-4, ura-1, ura-3) are not linked to each other or to ura-2, the gene for carbamoyl phosphate synthetase and aspartic transcarbamylase. Mutants that have simultaneously lost feedback inhibition by uridine triphosphate for carbamoyl phosphate synthetase and for aspartic transcarbamylase have been found and mapped in the gene ura-2.
280 citations
TL;DR: The properties of organic semiconductors, especially polyanilines, are reviewed in this article in the light of recent work, and the properties of the polyaniliines are discussed in detail.
256 citations
TL;DR: Lecithin–water systems display a variety of phases, several of which belong to a class of structures recently discovered in the anhydrous divalent cation-soaps, which are clustered in rod-shaped regions, embedded in a disordered paraffin matrix.
Abstract: Lecithin–water systems display a variety of phases. Several of these phases, observed at a high temperature in the presence of small amounts of water, belong to a class of structures recently discovered in the anhydrous divalent cation-soaps. In these structures the polar groups are clustered in rod-shaped regions, embedded in a disordered paraffin matrix. In one of the phases the rods are infinitely long; in two others the rods are of finite length, and join three by three, forming two and three-dimensional networks.
245 citations
TL;DR: In this article, the authors calculate l'energie de cohesion and the tension superficielle des metaux de transition en fonction du remplissage de la band d dans l'approximation des liaisons fortes isotropes dans un cristal cubique simple.
199 citations
TL;DR: In this article, the equilibrium properties of a single strand of dAT copolymer with a double helix with a loop at one end (hairpin) are studied by a propagator method.
Abstract: At low temperatures a single strand of dAT copolymer tends to form a double helix with a loop at one end (hairpin). At slightly higher temperatures a branched structure (consisting of many hairpins connected by coiled regions) appears. The equilibrium properties of this branched structure are studied here by a propagator method. In particular the radius of gyration RG is calculated; under typical conditions, RG is expected to show a minimum at a temperature slightly below melting, in agreement with viscosity measurements. The present calculation is restricted to rather sharp transitions, for which the size of each helical region is large, even at the melting point. Then, in a rather broad range of molecular weights, M, RG is proportional to M1/4(as in the Zimm-Stockmayer theory of simple branched polymers).
125 citations
TL;DR: Differences between rat and guinea-pig AP and the possible participation of Ca ions in the genesis of the ventricular AP are discussed and changes in contraction and AP during potentiation are opposite.
121 citations
TL;DR: A microcalorimetric method for measuring the influence of extracellular glucose concentration on the rate of catabolism is described and seems to be widely applicable to kinetic studies of the permeation of metabolizable substrates in microorganisms.
Abstract: A microcalorimetric method for measuring the influence of extracellular glucose concentration on the rate of catabolism is described. This method has been applied to anaerobically growing cultures of Zymomonas mobilis and of a respiratory-deficient ("petite") mutant of Saccharomyces cerevisiae (strain YFa). The Michaelian kinetics recorded with both organisms were apparently related to glucose transport. With Z. mobilis, it was found that, in the range of glucose concentrations at which this organism was growing exponentially, cell activity was limited by the maximal rate of the catabolic enzymes; at lower concentrations, glucose transport was the rate controlling step. The metabolic activity of yeast always depended on external glucose concentration; when this was lowered under a threshold, a change of kinetics took place. The microcalorimetric method described seems to be widely applicable to kinetic studies of the permeation of metabolizable substrates in microorganisms.
96 citations
TL;DR: In this paper, conditions de preparation des different manganites spinelles MeMn2O4 (Me = Cr, Mn, Fe, Co, Ni, Cu et Zn) and leurs zones de stabilite en phase unique sont decrites.
95 citations
TL;DR: An emission line of CuC1 is observed at low temperature when the crystal is excited by high intensity u.v. laser light as discussed by the authors, but it is not observed with low intensity.
95 citations
TL;DR: In this article, the authors propose a method to solve the problem of homonymity in homonymization, i.e., homonymisation of homonyms.Resumé
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83 citations
TL;DR: In this article, a calculation of the electronic structure of the bases of DNA has been performed by an SCF procedure including simultaneously all the valence electrons, and the results are analyzed and compared to those of previous calculations made in the π electron approximation.
Abstract: A calculation of the electronic structure of the bases of DNA has been performed by an SCF procedure including simultaneously all the valence electrons. The results are analyzed and compared to those of previous calculations made in the π electron approximation.
TL;DR: The notion of acidite generalisee (echange de Cl − ) dans le tetrachloroaluminate de sodium fondu as discussed by the authors is a developpee.
TL;DR: In this paper, a detailed calculation of the relaxation matrix of resonance atomic states by resonant collisions is carried out in the semiclassical impact theory, and the validity of different approximations is discussed.
Abstract: A detailed calculation of the relaxation matrix of resonance atomic states by resonant collisions is carried out in the semiclassical impact theory. The validity of the different approximations is discussed. These results have been tested by observing self-broadening of level-crossing curves in high field and in zero field, in the $6^{3}P_{1}$ state in mercury. Observation of these signals at high pressures is very difficult with a pure isotope because of strong absorption and trapping of resonance light in the vapor; it is made very easy by observing level-crossing signals of one isotope in a very low concentration in the vapor of another isotope. Collisions between the different pairs of mercury isotopes have been thus systematically studied. Results are in excellent agreement (10%) with theory, both for the absolute value of cross sections and for the ratio of orientation broadening to alignment broadening.
TL;DR: Measurements of the birefringence of sapphire, magnesium fluoride, and synthetic quartz are reported and a discussion of the methods of achromatizing quarter-wave plates and of linearizing the path retardation of a multiwave plate against wavelength (equichromatic wave plates).
Abstract: Measurements of the birefringence of sapphire, magnesium fluoride, and synthetic quartz from 3000 A to 1500 A are reported and are followed by a discussion of the methods of achromatizing quarter-wave plates and of linearizing the path retardation of a multiwave plate against wavelength (equichromatic wave plates).
TL;DR: Les resultats d'analyse permettent de rassembler les especes en groupes chimiquement homogenes, qui correspondent le plus souvent avec les sections ou sous-sections du genre etablies sur des criteres botaniques.
TL;DR: Une interpretation de the variabilite de the composition des latex d'Euphorbes en triterpenes peut etre tiree de ces resultats.
01 Jan 1968
TL;DR: The most fascinating aspects of brain activity are periodic ones, recorded under various conditions: e.g., as recurring electrical patterns in ‘spontaneous’ activities, and as after-discharges following peripheral stimulation or ensuing from direct stimulation of the brain.
Abstract: The most fascinating aspects of brain activity are periodic ones, recorded under various conditions: e.g., as recurring electrical patterns in ‘spontaneous’ activities, and as after-discharges following peripheral stimulation or ensuing from direct stimulation of the brain.
TL;DR: In this paper, the superconducting properties of small metallic crystallities S coated with a polarizable material P were studied. At the vicinity of the S P interface, there are two mechanisms which can favor superconductivity: (1) the phonon spectrum is modified; (2) the electrons can be attracted through the exchange of a polarization wave of the dielectric.
TL;DR: This article showed that the discriminability of the two categories of stimuli cannot explain the differences in VRT since the motor reaction time and the recognition threshold are a little higher for words than for drawings.
Abstract: Verbal reaction time to drawings is always a little longer than verbal reaction time to words. In previous experiments this finding had been interpreted in terms of the greater uncertainty when naming a drawing than when reading a word. In the present experiment, it is shown that the discriminability of the two categories of stimuli cannot explain the differences in VRT since the motor reaction time and the recognition threshold are a little higher for words than for drawings.
TL;DR: In this paper, the Stockman-fixman method has been applied to determine the unperturbed dimensions of a polymer chain from viscosity measurements on several fractions in a good solvent.
Abstract: The STOCKMAYER-FIXMAN method has been applied to determine the unperturbed dimensions of a polymer chain from viscosity measurements on several fractions in a good solvent. Homopolymers yield values of the unperturbed dimensions which are independent of the nature of solvent and which hardly depend upon temperature.
Using the same method for [η] measurements in different solvents, the values obtained for random copolymers PS–PMMA are quite different from the “ideal” values calculated on the basis of additivity rules from the unperturbed dimensions of corresponding homopolymers. The discrepancy was shown to depend on the χAB parameter, which also governs the critical concentration for phase separation for a solution of the corresponding homo polymers.
Since χAB is solvent and temperature dependent, the observed variation in the unperturbed dimensions from one solvent to another can be qualitatively explained. Linear relation was found between χAB and KΘ leading to KΘ “ideal” for χAB = 0.
Moreover, the temperature dependence of unperturbed dimensions for a random copolymer, in a given solvent, is much stronger than for an homopolymer. As temperature increases χAB decreases and the unperturbed dimensions approach the “ideal” values.
These results show the influence of heterocontact interactions on chain conformation. They clearly demonstrate their importance at theta conditions by influencing the dimensions of the chain.
Die STOCKMAYER-FIXMAN-Methode wurde angewendet, um die ungestorten Dimensionen einer polymeren Kette aus Viskositatsmessungen an verschiedenen Fraktionen in einem guten Losungsmittel zu. bestimmen. Homopolymere ergaben Werte der ungestorten Dimensionen, die von der Natur des Losungsmittels unabhangig sind und von der Temperatur wenig abhangen.
Wenn man die gleiche Methode zur Bestimmung von [η] in verschiedenen Losungsmitteln anwendet, dann sind die fur statistische Copolymere PS–PMMA erhaltenen Werte erheblich verschieden von den „idealen” Werten, die auf der Grundlage der Additivitatsregeln aus den ungestorten Dimensionen der entsprechenden Homopolymeren berechnet werden. Es wurde gezeigt, das diese Diskrepanz von dem χAB-Parameter abhangt, der auch die kritische Konzentration fur die Phasentrennung einer Losung der entsprechenden Homopolymeren beherrscht.
Da nun χAB losungsmittel- und temperaturabhangig ist, kann die beobachtete Variation der ungestorten Dimensionen von einem Losungsmittel mm anderen qualitativ erklart werden. Es wurde eine lineare Beziehung zwischen χAB und KΘ gefunden, die zu einem KΘ „ideal” fur χAB = 0 fuhrt.
Ferner ist die Temperaturabhangigkeit der ungestorten Dimensionen eines statistischen Copolymeren in einem gegebenen Losungsmittel viel starker als bei einem Homopolymeren. Mit steigender Temperatur fallt χAB, und die ungestorten Dimensionen nahern sich den „idealen” Werten.
Diese Ergebnisse werfen Licht auf den Einflus der Heterokontaktwechselwirkungen auf die Kettenkonformation. Sie zeigen in klarer Weise die Bedeutung dieser Wechselwirkungen unter Thetabedingungen dadurch, das sie die Dimensionen der Kette beeinflussen.
TL;DR: In this article, the Stockmayer-Fixman extrapolation was applied to the date: it yields the unperturbed dimensions K θ of the chain, which is a unique value for a given polymer in all pure solvents, as expected; in the case of binary mixtures, the unique value is found higher or lower than this unique value, depending upon the thermodynamic parameter x 12 characterizing the solvent mixture.
TL;DR: In this article, the screening of the 7s electron charge density at the nucleus by 6d, 7s, and 7p electrons was discussed, and it turns out that the same screening factors as for the 6s electron in lighter elements can be used.
Abstract: The isotope shifts of unperturbed electron configurations have been determined from isotope shift measurements in the spectra of Th, U, Pu, and Am. The screening of the 7s electron charge density at the nucleus by 6d, 7s, and 7p electrons is discussed. It turns out that the same screening factors as for the 6s electron in lighter elements can be used. The screening of the 7s electron charge density at the nucleus by one 5f electron amounts to about 25%: [δT(fns)−δT(fn)]/[δT(fn}s)−δ(fn})]=0.75. The charge density at the nucleus due to the filleds (andp1/2) shells is considerabely screened by anf electron. The isotope shiftδT(fn}-1dm+2)−δT(fndm) produced by this effect is of the same order of magnitude as the isotope shiftδT(fndms)-δT(fndm) due to ans electron. The experimental isotope shift constants are found to be:Β Cexp(Th230–Th232)=880±120;Β Cexp(U233–U235)=1000±180;Β Cexp(U234–U236)=1070±200;Β Cexp(U236–U238)=1080±180;Β Cexp(Pu238–Pu240)=1200±120;Β Cexp(Pu239–Pu241)=1060±100;Β Cexp(Pu240–Pu242)=900 ±90;Β Cexp(Am241–Am243)=890±50 [10−3cm−1]. The ratiosΒ Cexp/Cth are discussed.
TL;DR: In this paper, a lower bound on the momentum derivative of the phase shifts was derived from the combination of unitarity, crossing, and analyticity in the domain resulting from axiomatic field theory.
Abstract: A lower bound on the momentum derivative of the phase shifts, $\frac{d{\ensuremath{\delta}}_{l}}{\mathrm{dk}}$, is derived from the combination of unitarity, crossing, and analyticity (in the domain resulting from axiomatic field theory). As an application, a lower bound for the ${\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$ scattering length is deduced.
01 Jan 1968
TL;DR: Les spectres infrarouges des cristaux de purine and of purine (D)-7 a 25 and 180 °C, ont ete etudies de 4 000 a 33 cm-1 ; les spectres inrarouge and Raman des solutions aqueuses of ces de two composes ont eite examines dans la region de 1 700 a 400 cm- 1. Une tentative d'attribution des bandes fondamentales est proposee as mentioned in this paper.
Abstract: Les spectres infrarouges des cristaux de purine et de purine (D)-7 a 25 et — 180 °C, ont ete etudies de 4 000 a 33 cm-1 ; les spectres infrarouges et Raman des solutions aqueuses de ces deux composes ont ete examines dans la region de 1 700 a 400 cm-1 . Une tentative d’attribution des bandes fondamentales est proposee. Huit bandes dues aux vibrations intermoleculaires ont ete identifiees dans l’infrarouge lointain. Quelques caracteristiques spectroscopiques de la forte liaison hydrogene NH...N de la purine autoassociee sont interpretees.
TL;DR: In this article, le flux limite de diffusion en regime turbulent and en regime laminaire is investigated. But the results of the diffusion convective in regime turbulent do not reste proportionnelle a la racine carree de l'electrode.
TL;DR: In this article, it was shown that at room temperature, the shear modulus at which the extrapolated value of $Q$ goes to zero may be somewhat different from the temperature at which it is actually zero in the normal state, which may explain the failure of some samples to undergo the martensitic phase transition.
Abstract: The temperature ${T}_{0}$, at which the shear modulus $\frac{1}{2}({C}_{11}\ensuremath{-}{C}_{12})$ vanishes in the cubic phase and in the normal state of some high superconducting $\ensuremath{\beta}$-W compounds, is calculated as a function of the small number $Q$ of electrons (or holes) in the nearly empty (or nearly full) $d$ subband. The variation of ${T}_{c}$ with $Q$ was calculated in a previous paper. We show that ${T}_{0}$ is much more sensitive than ${T}_{c}$ to the value of $Q$, and thus to the exact chemical composition of the ${A}_{3}B$ phase. Moreover, we show that when $Q$ falls in some range of its value, a linear extrapolation at low temperatures cannot be used to obtain the value of ${T}_{0}$. [In other words, the temperature ${{T}_{0}}^{\ensuremath{'}}$ at which the extrapolated value of $\frac{1}{2}({C}_{11}\ensuremath{-}{C}_{12})$ goes to zero may be somewhat different from the temperature ${T}_{0}$ at which $\frac{1}{2}({C}_{11}\ensuremath{-}{C}_{12})$ is actually zero.] The failure of some samples to undergo the martensitic phase transition, when the extrapolated value of $\frac{1}{2}({C}_{11}\ensuremath{-}{C}_{12})$ seems to go to zero in the normal state, may be explained in this way. Finally, we find that at room temperature $\frac{1}{2}({C}_{11}\ensuremath{-}{C}_{12})$ is minimum for some small value of $Q$.