Showing papers by "University of Paris published in 1968"

Receptive fields of single cells in the cat's superior colliculus.

Abstract: Receptive field analysis of single units in the superior colliculus of the mid-pontine, pretrigeminal cat has confirmed previous reports of directionally selective units in the tectum. The directional property was based principally upon a unilateral inhibitory mechanism, although some directional responses to small moving objects depended equally upon summation of excitation. Receptive field size varied greatly, with field diameters not uncommonly exceeding 30 degrees. Fields near the area centralis and along the horizontal meridian tended to be smaller than those elsewhere. An inhibitory influence from the field periphery was demonstrated.

Correlation Coefficients for Electronic Wave Functions

Abstract: Electron correlation in atoms and molecules can be analyzed in terms of correlation coefficients similar to those used in probability theory and mathematical statistics. Different correlation coefficients can be defined for angular, radial, and momentum correlation in atoms and for axial (left-right), equatorial, and radial (in-out) correlation in molecules. The correlation coefficients are closely related to certain coefficients of the so-called natural expansion of the wave function. Nonvanishing correlation coefficients are obtained for the Fermi correlation in the independent-particle model as well as for electron correlation proper. Numerical examples show that the correlation coefficients for atoms are of the order of -0.05, suggesting that the correlation is usually small and negative, as compared with \ifmmode\pm\else\textpm\fi{}1 for "perfect" correlation. However, positive correlation coefficients may occur, in particular for excited states. Correlation in supersystems consisting of two nonoverlapping systems at large distances, and the distinction between interorbital and intraorbital correlation, are also discussed.

Sleep ontogenesis in early human prematurity from 24 to 27 weeks of conceptional age

Abstract: The spontaneous behavior of 5 previable human prematures born between 24 and 27 weeks of gestational age and weighing between 600 and 900 g was studied, between the 3rd and 30th hr of life. Death occurred between the 28th and 120th hr. Body motility, eye movements, respiratory and cardiac rhythms, chin myogram, electroencephalogram (EEG), and crying were evaluated by careful observation and by polygraphic recordings for periods of from 1 to 2 hr. A very rich and continuous motility is described consisting of rapid jerks, either diffuse or localized, and of slow movements. Rhythmic movements of the chin or peribuccal area occur in bursts and are particularly striking. The paucity of rapid eye movements (REM) is also remarkable. The EEG is composed of silent periods interrupted by discontinuous polymorphic activity. The fixation of the cardiac rate, the absence of periodic respiration and of apneic periods are the most important vegetative phenomena. Crying occurs in short periods rarely lasting more than 20 sec. The state of these previable prematures cannot be considered as waking; it seems to be a very immature state of sleep that differs from both the quiet and the active sleep of full-term newborns. This atypical sleep, which appears to be present in other species characterized by a great degree of immaturity at birth, does not give any evidence of cyclic organization.

On the calculation of London–Van der Waals interactions in a monopole‐bond polarizability approximation with application to interaction between purine and pyrimidine bases

Abstract: Methods for calculating intermolecular interaction energies are evaluated in a specific application to double-stranded DNA-like configurations between bases. The total interaction is decomposed in such a way, that existing methods can be hybridized so that each method can be utilized to its best advantage. In addition, a new method is suggested for the computation of the dispersion interaction between the σ-electron system of one molecule and the π-electron system of the other. Results of various approaches applied to base pairs and double-stranded dimers are summarized and compared in a number of tables. Des methodes differentes pour le calcul des energies d'interaction intermoleculaire ont ete comparees dans une application a des configurations de type ADN a deux chaines. L'interaction totale a ete decomposee en parties differentes pour permettre des combinaisons optimales des methodes existantes. On propose une methode nouvelle pour calculer l'interaction de dispersion entre les electrons σ d'une molecule et les electrons π d'une autre. Les resultats ont ete condenses dans un grand nombre de tablaux. Methoden fur die Berechnung intermolekulare Wechselwirkungsenergien werden in Anwendungen auf Konfigurationen von DNA-Typ zwischen Basen verglichen. Die Gesamtwechselwirkung wird in solche Teilen zerlegt, die optimale Kombinationen der existierenden Methoden gestatten. Es wird eine neue Methode fur die Berechnung der Dispersionswechselwirkung zwischen den σ-Elektronen eines Molekuls und den π-Elektronen eines anderen vorgeschlagen. Die Resultate sind in Tabellen zusammengefasst.

Aspects of the Electronic Structure of the Purine and Pyrimidine Bases of the Nucleic Acids and of Their Interactions

Abstract: Publisher Summary This chapter presents the aspects of the electronic structure of the purine and pyrimidine bases of the nucleic acids and of their interactions It discusses refined molecular orbital calculations on the purine and pyrimidine components of the nucleic acids followed by purine-pyrimidine interactions The self consistent field molecular orbital method calculations are done for the purine and pyrimidine components of the nucleic acids, within the limits of the Parker-Pople-Parr approximation All these calculations have adopted the usual hypothesis of σ – π separation and dealt essentially with the system of π electrons in the field of the σ core The most elaborate of these calculations and which has also been used the most extensively in relation with the physicochemical and biochemical properties of these compounds are those due to Berthod The chapter presents the results of this work, pointing out occasionally; however, its relation to other similar calculations and to the previous results is obtained within the Huckel scheme

In vitro Detection of Immunosuppressive Activity of Anti-lymphocyte Sera

Abstract: THE problem of in vitro evaluation of anti-lymphocyte sera (ALS) has not yet been solved. The tests used, such as leuco-agglutination, cytotoxicity and lymphocyte stimulation in culture, do not detect small amounts of anti-lymphocyte antibodies and, furthermore, the results of these tests are not regularly correlated with graft survival time1,2. We propose a new in vitro test, based on inhibition of an active function of the lymphocytes.

Molecular orbital calculations on the preferred conformation of nucleosides

Abstract: The extended Huckel theory has been applied to the study of the conformation of the nucleosides of the purine and pyrimidine bases of the nucleic acids. Although the evaluation of the total energy as a function of the rotation angle presents in all cases two minima, the calculations predict a preferred anti conformation for uridine, cytidine and adenosine and a preferred syn conformation for guanosine. These predictions appear to be in agreement with the available experimental data.

Polarization of the fluorescence light of ne atoms interacting with a laser beam: Measurement of several relaxation times

Abstract: The fluorescent light from two atomic levels is studied assuming that the atoms are subjected to a gas discharge, to a static magnetic field, and, simultaneously, to a laser beam having the transition frequency between the atomic levels. Calculations are developed in the formalism of irreducible tensor operators. One takes into account the existence of isotropic relaxations and cascade effects due to spontaneous emission between the upper and the lower levels. Following Lamb, the laser beam is described classically by its electric field, and its effects are calculated by perturbation theory. It is predicted that the σ component of fluorescent light exhibits the Hanle effect, which allows one to measure the relaxation rates \Gamma(0) and \Gamma(2) of the population and of the alignment of the emitting level, respectively. Experimental agreement with the theoretical analysis has been found for the 3s_{2}, 2s_{2} , and 2P_{4} levels of Ne. Among the experimental results obtained by this method are the natural widths and the collision cross sections for population (quenching collision) and for alignment. Several transition probabilities are also derived. Furthermore, the theory of coherent imprisonment of the fluorescent line has been found valid even if laser pumping light is used.

Sustained spontaneous activity of Ranvier nodes induced by the combined actions of TEA and lack of calcium.

Abstract: Superfusion of a Ranvier node ofr. esculenta andxenopus l. with Ringer's of reduced Ca++-content (0.05 to 0.1 mM/l) containing 5 mM/l TEA, induced spontaneous activity for more than 30 min. The frequency of discharge at beginning of superfusion was 192±39/sec. It declined within 30 to 60 sec to a steady value of 76±26/sec. Such membranes were submitted to voltage clamp analysis: Depolarisations betweenV=0 and 20 mV produced initial, between 0 and 10 mV steady state inward currents. This reversal of steady state currents compared to normal membranes is due to enhanced Na+-permeability (lack of Ca++) and to reduced K+-permeability (action of TEA). Analysis of the sodium system revealed (a) shift of them ∞ (V) curve by 10 mV to smaller depolarizations (b) shift of theh ∞ (V) curve in same direction by 5 mV (c) little change of time constantsτ m andτ k. The productm ∞ 2 h ∞ near the resting potential differs from zero. Spontaneous activity can thus be explained by the following cycle: After repolarization of the spike the nearly abolished sodium permeability grows toward its steady state value (h→h ∞,m≈m ∞). Accordingly the sodium inward current increases with the evolution ofh and produces a depolarization (pacemaker potential) which by the early rise of the variablem becomes regenerative and leads to the next spike.

All valence-electrons calculations on purines and pyrimidines

Abstract: An iterative extended Huckel calculation (IEHC) has been performed for the purine and pyrimidine bases of the nucleic acids. The results presented concern the electron distribution and the dipole moments, the atomic orbital populations and the “hybridization” ratios, the energies of the molecular orbitals and the ionization potentials. In particular, the relative orders of the dipole moments and of the π-ionization potentials are correctly reproduced but their absolute values are too great.

Evoked responses and neuronal activity in the lateral geniculate

Abstract: Il a paru interessant de preciser les relations de temps et de phase entre la reponse evoquee massive et la reponse des neurones du corps genouille lateral. Des microelectrodes ont ete implantees dans le corps genouille lateral du chat et des reponses ont ete evoquees par stimulation visuelle. On a pu demontrer que la probabilite aussi bien que la frequence de la decharge neuronique varient en raison de la premiere derivee de la reponse massive a ondes lentes.

The true dibenzo [a, l] pyrene, a new, potent carcinogen

Abstract: I m Gegensa tz zu d e m pf lanzl ichen W u c h s s t o f f Kinet in , e inem 6-Pury l fu ry lamin , zeigen einige 6 -Pury lde r iva t e biogener Amine, so des T r y p t a m i n s [t ] u~ld des t~2istamins (I) [2], auch cy to tox i sche W i r k u n g e n an t ier ischen Ze]len. I i s t dabei du rch seine spezifisehe W i r k u n g auf mal igne Zellen in vi t ro gekennze ichne t [3]. Unsere U n t e r s u e h u n g e n fiber den e n z y m a t i s c h e n A b b a u yon I h a b e n gezeigt, dab es du rch X a n t h i n o x y d a s e in das 2 , 8 D i h y d r o x y p u r i n D e r i v a t (das keine cy to tox i sche Wirk u n g hat) f ibergeffihrt wird, welches von Perox idasen u n d H~O~ in kleinere Spal ts t f ieke zerlegt wird [4]. W i t h a b e n inzwischen gefunden, dab der A b b a u von I in e inem t ier ischen O r g a n i s m u s in /~hnlicher Weise verlS.uft. Die im Ur in nach Ver f f i t t e rung yon ]~C-markier tem I ausgesch iedenen P r o d u k t e en t sp rechen inl R a d i o c h r o m a t o g r a m m den durch enzyma t i schen A b b a n in vi t ro e rha l tenen . Auch m i t isolierten Zellen Iiessen sich O x y d a t i o n s p r o d u k t e erhal ten. Bei Bebr f i tung mi t einer Suspens ion you Leberzel len bei 37 ~ wird I in 3 Std in das 8 H y d r o x y u n d 2 ,8 -D i hyd roxy -Der i va t fibergefflhrt. Ex pe r imen te [5], wonach I du t ch Leberzel len in ein Pur in u n d ein Imidazo l -Der iva t gespa l ten werden solI, erwiesen sich als n ich t reproduzierbar . 1VLit Zellen des Ehr l i ch ' s chen M~useAsc i t e s -Tumors t r a t u n t e r gleiehen B e d i n g u n g e u keine Ver~ n d e r u n g yon I ein. Dieser ers te O x y d a t i o n s s c h r i t t f indet d a n a e h bei Tumorze l l en n ich t s t a t t u n d dahe r bleibt die cytotoxisehe W i r k u n g yon I diesen gegent~ber erhal ten. Wir beschfift igen uns welter m i t dem Verha l t en versch iedener normale r u n d mal igner Zel lar ten gegen I u n d mi t der Pri~fung der Frage, ob das F e r m e n t der u n t e r s u c h t e n Zellen m i t X a n t h i n oxydase ident i sch oder ihr nur /~hn l ich ist. D e m B u n d e s m i n i s t e r i u m fgr wissenschaf t i iche F o r s c h u n g danken wir fflr die F 6 r d e r u n g der Arbe i ten ( F 6 r d e r u n g s v o r h a b e n St. N 6~0-67).

Neurophysin and neurohypophysial hormones.

Abstract: Following the discovery of the pressor, oxytocic and antidiuretic effects of posterior pituitary extracts, about 50 years ago, there have been two opposing views: one held by Abel and his co-workers (Abel, Rouiller & Geiling 1923; Abel 1930), according to which the oxytocic, pressor and antidiuretic properties belong to a single substance, and that of Dudley (1919), who considered that these activities were due to different substances. The first conception led MacArthur (1931) and later van Dyke and his collaborators (van Dyke, Chow, Greep & Rothen 1942) to isolate an apparently pure protein which possessed the three activities in ratios resembling those found in crude extracts of the gland. The second concept led Kamm (Kamm et al . 1928) and later du Vigneaud (1952), Fromageot and his colleagues (Acher & Fromageot 1955) to purify two different active principles: the one, oxytocin possessing oxytocic and milk-ejecting properties, the other, vasopressin possessing the pressor and the antidiuretic activities. The problem therefore was to determine if the van Dyke protein was the true hormone, oxytocin and vasopressin being only degradation products which retain the activities or whether the two peptides were the natural hormones, the van Dyke protein being a kind of common precursor or a storage form.

Electronic factors in the photodimerization of thymine

Abstract: — The role that quantum chemistry has played in the understanding of the photochemistry of pyrimidines is outlined. A variety of increasingly sophisticated calculations have shown that electronic excitation is localized largely at the double bond between carbons 5 and 6, which is the position of photodimerization in thymine. So far, the theoretical procedures have not been sufficient to permit a distinction between different multiplicities for the excited levels, but refer only to a “first excited state”. A discussion is given of why more extended calculations are necessary before any statement can be made as to whether it is the singlet or the triplet that is involved in thymine photodimerization. RESUMEN El rol que la quimica cuantica ha jugado en la comprension de la fotoquimica de las pirimidinas ha sido delineado. Una gran variedad de calculos cada vez mas sofisticados ha mostrado que la excitation electronica esta localizada en la doble union C-5-C-6, la cual es la posicion de dimerizacion en la timina. Hasta el presente, los procedimientos teoricos no han sido suficientes para permitir una distincion entre diferentes multiplicidades para los niveles excitados, pero se refieren solo al primer estado excitado o por lo menos al nivel triplete. Se presenta una discusion para justificar la necesidad de calculos mas extensivos antes de que se pueda sacar la conclusion de si es el estado triplete o el singuiete el que esta envuelto en la fotodimerizacion de la timina.

Factorization and Constraints in Regge-Pole Theory

Abstract: The behavior near zero momentum transfer of the Regge residues for a two-particle reaction is determined by means of analyticity and factorization. It is shown that, at least in all cases of present interest, the solution obtained satisfies the kinematical constraints provided that a classification and certain relations between the trajectories involved (identical to those obtained by group-theoretical methods) are imposed.

L’Ignimbrite et la Caldera de Batur (Bali, Indonesie)

Abstract: L’ile de Bali est constituee de deux unites distinctes: une chaine de breches volcaniques a l’Ouest, une serie de volcans actifs a l’Est. Ceux-ci comprennent le strato-volcan Agung et les deux grandes calderas Tjatur et Batur. Cette derniere resulte de l’effondrement d’un strato-volcan consecutivement a l’emission, il y a 22.000 ans, d’une nappe d’ignimbrites que l’on retrouve au nord et surtout — largement etalee — au sud du Batur.

Rôle de la polarisation dans les moments dipolaires des complexes dits ≪ de transfert de charge ≫

Abstract: Nous montrons que les effets de lapolarisation mutuelle des constituants permettent de rendre compte des observations relatives au moment dipolaire des complexes avec transfert de charge, de typeπ-π: apparition d'un moment dipolaire dans un complexe forme entre deux constituants apolaires, ou modification du moment dipolaire d'un compose lorsqu'il s'associe avec un compose apolaire.

The activity of neurons in the lateral geniculate body during wakefulness and natural sleep.

Abstract: On a montre que l'activite neuronique du corps genouille externe du chat diminue lorsque l'animal passe de l'eveil au sommeil a ondes lentes, et augmente lorsque l'animal passe au sommeil a ondes rapides de bas voltage.

Some Effects of Protonation on the Electronic Structure of Pyridine and Cytosine

Abstract: The effects of protonation on the charge distributions of pyridine and cytosine are investigated with the help of the Iterative Extended Huckel technique. The polarization of the σ-electrons is then included explicitly in a Pariser-Parr-Pople computation of the π-π* transition energies of the pyridinium and cytosinium ions.

Influence of σ systems on the ππ* transition energies: A simple application to the series of linear polyenes

Abstract: One uses a 2nd order perturbation expression of the transition energies for the series of linear polyenes with π delocalized molecular orbitals and σ fully localized bond molecular orbitals. One only keeps the σπ coulombic integrals and the local σσ * excitations. Within these assumptions it is possible to demonstrate: the effect of the monoexcitations on CH and CC bonds mainly depends of the pairing or non pairing character of the considered ππ * transition. It tends to zero as n −1 as the dimension n of the system increases. the rOle of the $$\begin{array}{*{20}c} \sigma \\ \pi \\ \end{array} \left| {\begin{array}{*{20}c} {\sigma *} \\ {\pi *} \\ \end{array} } \right.$$ excitations increases as n increases and tends towards a limit which depends of the considered ππ * transition. But the asymptotic final effect of σ system is smaller than for ethylene. the contribution of the σ system to the actual ππ * singlet triplet separation decreases towards zero when the dimension of the system increases.

Mechanism of photooxidation: Interpretation of the substituent effects in the photooxidation of acenic derivatives

Abstract: It has been observed that some substituents introduced in acenic derivatives are able to change the site of the fixation of oxygen during photooxidation. It is not possible to interpret this phenomenon by calculating the paralocalization energies. However, if an intermediate complex is introduced, which corresponds to an extension of the delocalized bond, a satisfactory explanation of the experimental results is possible. On a observe que certains substituants introduits sur un systeme acenique peuvent changer le lieu de la fixation de l'oxygene au cours de la photooxydation. Ce fait ne peut ětre interprete en calculant les energies de paralocalisation. L'hypothese d'un complexe intermediaire correspondant a une extension du systeme delocalise permet au contraire de rendre tres bien compte des resultats experimentaux. Es wurde bemerkt, dass gewisse Substituenten, die in Acenderivaten eingefuhrt sind, den Anheftungsplatz des Sauerstoffs wahrend der Photooxydation verandern konnen. Dieses Phanomen kann nicht mit einer Berechnung der Paralokalisierungsenergien erklart werden. Wenn aber ein intermediurer Komplex eingefuhrt wird, was einer Erweiterung der delokalisierten Bindung entspricht, ist es moglich eine befriedigende Erklarung der experimentellen Tatsachen zu geben.

( p , x p ) and ( p , x p y α ) Reactions of 156-MeV Protons with Light Targets ( A = 11 to A = 27 )

Abstract: The formation cross sections of ${\mathrm{Li}}^{9}$, ${\mathrm{C}}^{16}$, and ${\mathrm{N}}^{17}$ from B, C, ${\mathrm{N}}^{14}$, ${\mathrm{N}}^{15}$, ${\mathrm{O}}^{16}$, ${\mathrm{O}}^{18}$, F, Ne, Na, Mg, and Al targets bombarded with 156-MeV protons were measured by means of their neutron emission. The results were compared with calculations based on the two-step spallation mechanism. Certain reactions were shown to provide direct comparison with prompt cascade calculation. In general, the agreement between theory and experiment was good, and it is suggested that some discrepancies are attributable to the neglect of the effect of nuclear structure in the calculations. The importance of $\ensuremath{\alpha}$ emission in determining the pattern of spallation product cross section was demonstrated.