Showing papers by "École Normale Supérieure published in 1974"

Behavioral and electrophysiological evidence of pain inhibition from midbrain stimulation in the cat

Abstract: Midbrain stimulation in chronically implanted, awake cats in the vicinity of dorsal raphe nucleus evoked profound analgesia to peripherally applied noxious stimuli. Analgesia was not accompanied by other obvious sensory or motor deficits. The peripheral field of analgesia sometimes included the entire body and in other cases was restricted to the hindquarters. Analgesia generally outlasted brain stimulation by no more than 10 sec. Stimulation distant from dorsal raphe led to pronounced motor or emotional effects precluding an adequate test of analgesia. In anesthetized cats, effects of midbrain stimulation were studied on evoked activity in dorsal horn lamina 4 and 5 cells. Stimulation of wide regions of midbrain inhibited pain-evoked activity in most lamina 5 cells without affecting responses of most lamina 4 cells. In some lamina 5 cells, midbrain stimulation inhibited responses to noxious but not innocuous stimuli. The possible role of lamina 5 cells in nociception and the possible relationship between analgesia and lamina 5 cell inhibition are discussed.

The Effect of the Bainite Packet Size on Toughness

Abstract: 419-42. 2. N. A. Hill and J. W. S. Jones: s NueL Mater., 1961, vol. 3, pp. 138-55. 3. D. L. Douglass: Trans. Amer. Soe. Metals, 1961, vol. 54, pp. 322-30. 4. M. Garfinkle and R. G. Garlick: Trans. TMS-AIME, 1968, vol. 242, pp. 809-14. 5. D. G. Alexander and O. N. Carlson: Trans. TMS-AIME, 1969, vol. 245, pp. 2592-3. 6. E. A. Nesbitt and H. J. Williams: J. Appl. PIjys., 1955, vol. 26, pp. 1217-21. 7. Y. lwama, M. lnagaki and T. Miyamoto: Trans. Japan. Inst. Metals, 1970, vol. 11, pp. 268-74. 8. A. J. Perry and D. J. Rowcliffe: J. Mater. ScL, 1973, vol. 8, pp. 904-7. l o w vo id s e m i c o h e r e n t

Observation of Fine-Structure Quantum Beats Following Stepwise Excitation in Sodium D States

Abstract: We report the observation of fine-structure and Zeeman quantum beats in highly excited sodium $D$ states prepared, for the first time in a quantum-beat experiment, by stepwise excitation using two synchronously pulsed dye lasers. We have used this new technique to measure the previously unknown fine-structure intervals of levels $9D$ and $10D$ of sodium, the values being, respectively, 124.5\ifmmode\pm\else\textpm\fi{}1.5 and 91.5\ifmmode\pm\else\textpm\fi{}1 MHz.

Free radical cyclizations, XVII. Mechanistic studies

Abstract: Free radical cyclizations of the 4-phenylbutyl radical and analogues carrying naphthyl and vinyl groups instead of phenyl have been studied. A typical reaction scheme is given below involving closures to five- and six-membered rings. Competition rate studies for the various types of ring closure were performed with deuterated analogues. The results can be used as an efficient mechanistic tool for other radical processes, as exemplified for the Kornblum reaction between α-substituted p-nitrobenzyl chlorides with the anion of benzylcyanide in a two-phase system. The nature of (cyclic) byproducts supports and confirms the radical chain mechanism for such substitutions.

Electron Microscopic Localization of the Binding Sites of Escherichia coli RNA Polymerase in the Early Promoter Region of T7 DNA

Abstract: Escherichia coli RNA polymerase bound to T7 DNA has been studied in the electron microscope. By dark-field observation of specimens prepared by adhesion on positively charged films, we have located the binding sites of RNA polymerase on the physical map of T7 DNA. At a molar ratio of RNA polymerase to DNA smaller than or equal to 10, we found three strong binding sites at 1.15, 1.41 and 1.65 map units from the left DNA end. At higher ratios additional binding sites were occupied. Two of them were located at 0.6 and 3.3 map units from the left DNA end. Preliminary results are presented on the binding of RNA polymerase to T7 DNA in the presence of rifampicin, heparin, actinomycin D and ethidium bromide. Only heparin added to the enzyme and ethidium bromide added to the DNA template inhibited the formation of the binding complexes. It is suggested that the three strong binding sites correspond to the three strong initiation sites found by other workers in the early promoter region of T7 DNA.

[Calcium metabolism and acetylcholine release in the electric organ of Torpedo marmorata (author's transl)].

Abstract: Resume— Le metabolisme du'calcium a eteetudie dans l'organe electrique de la Torpille, au repos et en activite, in vivo et in vitro, en mesurant le calcium total et en utilisant du 45Ca. Lorsque le tissu est mis en presence de fortes concentrations de calcium, un echange complet s'effectue entre le calcium cellulaire et celui du milieu d'incubation. En presence de faibles concentrations, le tissu retient son calcium qui, dans ce cas, sechange mal avec l'exterieur. La stimulation cause une augmentation nette du calcium cellulaire et accelere son echange avec le milieu exterieur. Cette entree de calcium concerne principalement les terminaisons nerveuses presynaptiques car on l'observe aussi lorsque la transmission est bloquee par le curare qui agit au niveaja des electroplaques. Il semble que le calcium influence la repartition intracellulaire du transmetteur. En effet, l'entree presynaptique de calcium s'accompagne d'une diminution de l'ACh ‘liee’ (vesiculaire). Lorsque le tissu est incube dans une solution exempte de calcium, surtout en presence d'EDTA, la reponse electrophysiologique disparait; le taux d'ACh ‘libre’ (disponible) diminue alors, mais son ‘turnover’ augmente. Le calcium extracellulaire est donc necessaire au maintien du compartiment d'ACh immediatement disponible. Abstract— Calcium metabolism was studied in the electric organ of Torpedo, at rest and after electrical stimulation, in vivo and in vitro, by measuring total calcium and using 45Ca. Seasonal variations in the calcium metabolism were observed, summer animals being richer in the ion than winter ones. When the tissue was incubated in high calcium concentrations, complete exchange was obtained between cellular calcium and that of the external medium. In the presence of low concentrations, the tissue retained its calcium which, in this case, was poorly exchanged. Stimulation was accompanied by a net increase of cellular calcium and by acceleration of its exchange with that of extracellular space. This entry of calcium seems to involve mainly the presynaptic nerve endings, since it is also observed when transmission was blocked by curare which acts at the level of the postsynaptic electroplaques. Calcium may also influence the intracellular repartition of the transmitter. As a matter of fact, the presynaptic entry of calcium is accompanied by diminution of ‘bound’ ACh (vesicular ACh). When the tissue was incubated in a solution devoid of calcium, especially if EDTA was added, the electrical response disappeared; then ‘free’ ACh which is the immediately available compartment, decreased but its turnover rose. ‘Bound’ and ‘free’ ACh were also measured under various conditions of homogenization and the results discussed. It is concluded that extracellular calcium is required for the maintenance of the immediately available compartment of ACh.

Glutamate antagonists at a crayfish neuromuscular junction.

Abstract: As Kravitz et al.1 have pointed out, glutamic acid is at present the only candidate for the excitatory transmitter at crustacean neuromuscular junctions. The evidence is that1,2 glutamic acid is the most potent excitatory substance present in the crustacean central nervous system (CNS), whole peripheral nerves and isolated excitatory axons1,3–5; that the glutamic acid content in nerve extracts accounts for the whole of their excitatory activity on crustacean muscles1, and that the receptors to glutamate are localised at the same junctional spots as the receptors to the natural excitatory transmitter6. Also, both glutamic acid and the natural transmitter produce similar changes in the permeability of the postjunctional muscle membrane7–9 and in spite of a large background leakage, a significant release of glutamic acid can be evoked by stimulation of excitatory nerves1. There is also a selective uptake of glutamic acid at the neuromuscular junction which could provide an inactivation mechanism10. There is, however, no information on whether glutamate receptors have the same pharmacological properties as the receptors of the natural excitatory transmitter.

Déterminisme du sexe chez Tilapia macrochir et Tilapia nilotica : action de la méthyltestostérone dans l'alimentation des alevins sur la différenciation sexuelle ; proportion des sexes dans la descendance des mâles "inversés"

Abstract: L'administration de methyltestosterone a raison de 4 0 wg par gramme d'aliment a des alevins de T. nilotica et T. macvochir pendant deux mois a partir de la fin de l'incubation buccale par la mere, a conduit aux resultats suivants :- Chez T. nilotica, nous avons obtenu l'induction complete et fonctionnelle du sexe mâle chez tous les animaux traites. Certains d'entre eux ont fourni une descendance entierement femelle, revelant un genotype sexuel femelle, ainsi qu'une homogametie femelle.- Chez T. macrochir, nous avons observe l'induction de la papille genitale de type mâle, et des modifications anormales dans la morphologie de la tete ; a une exception pres, tous les animaux experimentaux etaient steriles, avec disparition complete de la lignee germinale chez la plupart d'entre eux.

Polyoma Viral DNA Replicated as a Nucleoprotein Complex in Close Association with the Host Cell Chromatin

Abstract: Polyoma viral DNA is shown to be replicated in close association with the mouse cell chromatin. Two virus-specific nucleoprotein complexes, designated complex A and B, can be dissociated from the isolated chromatin by gentle homogenization in 0.5 M NaCl. Complex A contains only replicating polyoma (Py) DNA whereas complex B contains only mature Py DNA I. The results show, furthermore, that complex A, containing viral DNA in different stages of replication, and complex B are both nucleoproteins with the same buoyant density. The data presently available suggest that newly synthesized stretches of Py DNA are immediately complexed with mouse cell histones and that complex B becomes the “core” of progeny Py virions. These results suggested that Py-induced replication of the mouse cell chromatin may be necessary to provide replicating Py DNA with histones.

Optical orientation of excitons in CdS

Abstract: The optical orientation by circularly polarized light of free and bound excitons in CdS is reported and discussed. The observed degrees of polarization are generally large and vary significantly with the exciting energy (a "negative" polarization is sometimes obtained). These results, together with the effects of a magnetic field, provide a lot of information about the levels excited, the luminescent levels (lifetimes and disorientation times), and the transfer of polarization from the first to the second. The optical orientation by linearly polarized light is also observed for the first time in solids. It is shown why these unusual effects can be seen on free excitons and not on other levels. The additional information that they provide leads to a better comprehension of the mechanisms of thermalization of the excitons, and of the symmetry properties of $K\ensuremath{ e}0$ exciton states.

Elastic Electron Scattering in Symmetry-Induced Zero-Gap Semiconductors

Abstract: Relaxation times for elastic electron scattering in the symmetry-induced zero-gap semi-conductors of zincblende structure are calculated, taking into account the nonparabolic character of the conduction band both in the density of states and the electron wave functions. The calculation is based on the band structure proposed by Groves and Paul and uses exact k · p solutions for the three-level model of Γ8, Γ6, and Γ7 levels. Electron scattering by charged impurities and heavy holes, optical phonons (screened polar interaction) and acoustic phonons is considered. Spin-flip transitions play an important role for all scattering modes. An anomalous q-dependence of the static dielectric function due to low energy excitations between the Γ8 heavy hole and conduction bands is shown to have small effect on the ionized impurity scattering at low temperatures. It is demonstrated that transverse modes give a large contribution to acoustic scattering. In all cases the Γ8 symmetry of the band-edge and the nonparabolicity of the band at higher energies have essential effect on the scattering processes. Es werden die Relaxationszeiten fur elastische Elektronenstreuung in den symmetrie-induzierten Null-Gap-Halbleitern mit Zinkblendestruktur berechnet, wobei der nicht-parabolische Charakter des Leitungsbandes sowohl bei der Zustandsdichte als auch bei den elektronischen Wellenfunktionen berucksichtigt wird. Die Rechnung basiert auf der von Groves und Paul vorgeschlagenen Bandstruktur und benutzt exakte k · p-Losungen fur das Drei-Niveau-Modell von Γ8-, Γ6- und Γ7-Niveaus. Elektronenstreuung durch geladene Storstellen und schwere Locher, optische Phononen (abgeschirmte polare Wechselwirkung) und akustische Phononen wird berucksichtigt. Spin-flip-Ubergange spielen eine bedeutende Rolle fur alle Streumoden. Es wird gezeigt, das eine anomale q-Abhangigkeit der statischen dielektrischen Funktion infolge niedriger Energieanregungen zwischen den schweren Γ8-Lochern und den Leitungsbandern nur einen geringen Einflus auf die Streuung durch ionisierte Storstellen bei niedrigen Temperaturen besitzt und das transversale Moden einen grosen Beitrag zur akustischen Streuung geben. In allen Fallen besitzt die Γ8-Symmetrie der Bandkante und die Nichtparabolizitat des Bandes bei hoheren Energien wesentlichen Einflus auf die Streuprozesse.

EPR measurements in ion-implanted diamond

Abstract: A new EPR spectrum, arising from defects in diamond created by boron, carbon, and nitrogen ion-implantation, is observed. The spectrum, lattice damage production, and annealing of damage are discussed and are ascribed to amorphous carbon. Ein neues EPR-Spektrum in Diamant wird beobachtet, das von Storstellen herruhrt, die durch Ionenimplantation von Bor, Kohlenstoff und Stickstoff erzeugt wurden. Das Spektrum, die Erzeugung und das Ausheilen der Gitterschaden werden diskutiert und dem amorphen Kohlenstoff zugeschrieben.

Estimation of the Critical Temperature of Electron-Hole Droplets in Ge and Si

Abstract: The evaporation of electron-hole droplets is studied. Even at the critical temperature ${T}_{c}$, the electron-hole density of the fluid is large enough that it is not so badly represented by a plasma model. ${T}_{c}$ is obtained using an expansion to the second order in $T$ of the chemical potential $\ensuremath{\mu}(T, {r}_{s})$ including correlation. The results of this crude method are in good agreement with experiments.

Numerical comparison of the Green's function and the Waterman and Rayleigh theories of scattering from a cylinder with arbitrary cross-section

Abstract: Until now much has been published of a theoretical nature concerning the validity or invalidity of the Rayleigh and Waterman methods for evaluating the field scattered from isolated perfectly conducting cylinders of arbitrary shape; however, little of conclusive, concrete nature has ensued. In the paper we propose to establish the conditions (if any) under which these methods may be employed with a reasonable degree of confidence in numerical applications. For this purpose, a description is given of one numerical technique appropriate to the Waterman theory, three numerical approaches to the Rayleigh theory and three numerical techniques for the now classical Green's function approach. The numerical results obtained from the latter are compared with those of the Rayleigh and Waterman methods in eighteen test cases covering a variety of cylinder shapes, incident angles and wavelengths. It is shown that the Rayleigh and Waterman methods yield accurate numerical results in all cases in which they lead to satisfactory verification of conservation of energy, and that all attempts fail to extract valid results from the Rayleigh theory in the case of oblique incidence on square and elliptical cylinders.

Blockade of the hydrosmotic effect of vasopressin by cytochalasin B

Abstract: La cytochalasine B dissocie les effets hydrosmotique et natriferique de la Pitressine sur la vessie de crapaud, en bloquant le transport d'eau sans pour autant modifier la stimulation du transport de sodium. Les interactions possibles entre le macrolide, les microfilaments et les alterations de permeabilite sont discutees.

Individualizing instruction in higher education: A review

Abstract: The salient characteristics of a variety of approaches to individualizing instruction are described and their respective merits with regard to higher education discussed. The review includes: programmed instruction, computer-assisted instruction and -management, information retrieval systems, audio-tutorial and modular instruction, contingency management and contracting, and personalized and individually prescribed instruction. While these approaches differ from each other in some respects, they all share an overriding concern for individual differences among students and seek to better adapt instruction to the learner. A section on general issues regarding the degree of individualisation, the role of the professor, institutional support for improving instruction, the role of the student, content and method, evaluation, and the future of individualized instruction concludes the review.

Infrarotspektroskopische Untersuchung des Borcarbids und seiner isotypen Derivate B12O2, B12P2 und B12As2

Abstract: Durch intensive Feinmahlung gelang es, B4C [ = B11C(CBC)], B12O2, B12P2 und B12As2 in eine fur infrarotspektroskopische Untersuchungen geeignete Form zu uberfuhren. B12O2 gibt das einfachste IR-Spektrum. Seine 5 Banden konnten durch eine Normalkoordinatenanalyse definierten Schwingungen der Atome in einer Elementarzelle zugeordnet werden. Davon ausgehend liesen sich die meisten Banden des B4C, bei welchem zusatzlich die Frequenzanderung durch 10B-Substitution gemessen wurde, sowie des B12P2 in Ubereinstimmung mit den bekannten Strukturprinzipien zuordnen. In beiden Spektren treten zusatzliche Banden auf, die mit Fehlordnungen in den Gruppen CBC bzw. PP zwischen den Ikosaedern erklart werden. Beim Borcarbid hangt das Ausmas dieser Fehlordnung offenbar vom B:C-Verhaltnis der Phase ab. Infrared Spectra of Boron Carbide and its Isotypic Derivatives B12O2, B12P2, and B12As2 From very finely powdered samples of B4C [ = B11C(CBC)], B12O2, B12P2, and B12As2 infrared spectra with very well shaped bands could be obtained. The spectrum of B12O2 with the smallest number of bands was assigned with the aid of a normal coordinate analysis. This gave a good basis for the interpretation of the spectra of normal and 10B-enriched B4C and of B12P2. Both are exhibiting some bands in addition to those expected for the ideal structures, which are explained by the assumption of disordering within the CBC resp. PP groups. At boron carbide this disorder seems to depend on the ratio B:C within its range of homogeneity.