Showing papers by "Centre national de la recherche scientifique published in 1972"

Ultrasounds and maternal behavior in small rodents.

Abstract: Rodent pups in distress emit 2 different types of ultrasonic calls. One is given in response to cold; the other in response to unusual tactile stimulation. The effects of these calls on adult behavior can also be classified into 2 categories. Some exert positive effects attracting the adult to the pup in distress and stimulating searching, retrieving, and nest-building. Others cause withdrawal of the adult from the pup thereby causing cesation of rough handling or aggression. The ultrasounds elicited by cold could exert the positive effects whereas those elicited by tactile stimulation produce the withdrawal effects.

Experimental Study of Zeeman Light Shifts in Weak Magnetic Fields

Abstract: According to the quantum theory of the optical-pumping cycle, one can describe the effect of a nonresonant light beam on the different Zeeman sublevels of an atomic ground state by an effective Hamiltonian ${\mathcal{H}}_{e}$ which depends on the polarization and spectral profile of the incident light. In order to check the structure of ${\mathcal{H}}_{e}$, we have performed a detailed experimental study of the ground-state energy sublevels of various kinds of atoms perturbed by different types of nonresonant light beams. Attention is paid to the modification of the Zeeman structure due to ${\mathcal{H}}_{e}$. We have been able to obtain experimentally in the ground state of $^{199}\mathrm{Hg}$, $^{201}\mathrm{Hg}$, and $^{87}\mathrm{Rb}$, Zeeman light shifts that are larger than the width of the levels due to the thermal relaxation. The removal of the Zeeman degeneracy in zero external field, due to a nonresonant light irradiation, is observed by different optical-pumping techniques; the full Zeeman diagram of the perturbed atoms is also determined when a static field ${\stackrel{\ensuremath{\rightarrow}}{\mathrm{H}}}_{0}$ is added. We have checked that the effect of ${\mathcal{H}}_{e}$ can be described in terms of fictitious static electric or magnetic fields. These fictitious fields can be used to act selectively on a given atomic level.

Theory of Saturated-Absorption Line Shapes

Abstract: A general theory of the saturated-absorption phenomenon in a two-level atomic system is developed, in which the phase relationships between the oscillating atomic dipoles as well as the population differences between energy levels are taken into account. The absorbing gaseous medium considered in this theory is subjected to irradiation by a quasi-running-wave composed of a strong pump field and a weak probe field propagating in opposite directions. Some new interesting results, not predicted by the so-called hole-burning or rate-equation model, are obtained. In particular, the probe-field-transmission peak line shape is found to be markedly different from what is expected according to the rate equations. For finite Doppler widths and a strong saturating pump field, absorption of the probe field can even change sign, and amplification of this field can actually occur. All these features are explained by a close inspection of the evolution of each atomic ensemble of given velocity. Detailed comparison with similar phenomena already observed in rf experiments is presented and permits us to clarify the new predicted effects.

[The network of the folliculo-stellate cells and the follicles of the adenohypophysis in the rat (pars distalis)].

Abstract: Dans l'hypophyse du rat, la microscopie electronique permet de mettre en evidence a l'interieur de tous les cordons epitheliaux de la pars distalis un reseau de cellules agranulaires: les cellules stellaires et folliculo-stellaires, satellites des cellules granuleuses hormonogenes. Les cellules de ce reseau se caracterisent a la fois par la multiplicite de leurs prolongements et par leur organisation autour de cavites pour la plupart submicroscopiques, «les follicules». Les cellules folliculo-stellaires correspondent a une partie des cellules chromophobes de la microscopie photonique.

Chromosomal location of mutations affecting sucrose metabolism in Bacillus subtilis Marburg.

Abstract: Mutations affecting sucrose metabolism have been mapped by PBS1 transduction on the Bacillus subtilis chromosome in seven loci sacA, sacB, sacQ, sacR, sacS, sacT and sacU. sacA and sacB are presumed to be the structural genes of a sucrase and a levansucrase respectively. sacR, sacS and sacT correspond to groups of mutations leading to constitutive synthesis of sucrase or both sucrase and levansucrase. In sacQ, sacS and sacU are located either mutations increasing the level of synthesis of levansucrase specifically (sacQ h , sacS h , sacU h ) or mutations abolishing specifically the synthesis of levansucrase (sacU − ). sacA, sacS and sacT map to the left of purA16. sacQ is located to the left of thr5, sacB and sacR between cysB3 and hisA1 and sacU between uvr1 and gtaB.

Pressure Effect on the Curie Temperatures of Transition Metals and Alloys

Abstract: We determined the variation of the Curie temperature with pressure for iron, cobalt, nickel, six iron-nickel alloys, and five cobalt-nickel alloys. A permeability method in zero magnetic field has been used in a belt-type apparatus at pressures up to 90 kbar and temperatures up to 1400 \ifmmode^\circ\else\textdegree\fi{}K. The pressure shifts measured for the Curie temperatures of iron and cobalt are zero; for nickel it is positive and markedly nonlinear. The Curie temperatures of face-centered-cubic iron-nickel alloys decrease very rapidly with pressure when the nickel content is low and show a progressively smaller decrease when nickel is added. They begin to increase when the nickel concentration is over 68 wt%. The existence of maxima on the curves of the Curie temperatures versus pressure or volume seems to be definitely established. pressure increases the Curie temperature of cobalt-nickel alloys in all cases, but here also in a nonlinear way. For strong ferromagnets with a few carriers a band theory has been previously developed. The shift of the Curie temperature is then given by $\frac{d\ensuremath{\theta}}{\mathrm{dP}}=\frac{5}{3}k\ensuremath{\theta}$ ($k=\mathrm{compressibility}$). For pure nickel and nickel-cobalt alloys with a cobalt content less than about 50 wt% good agreement with experiment is obtained at low pressures, but not at higher pressures. The Curie temperature shift of Invar-type alloys has been previously calculated using a weak-itinerant-electron-ferromagnet band theory. In this case we have been able to predict and observe a parabolic decrease of the Curie temperature with pressure: ${\ensuremath{\theta}}^{2}={\ensuremath{\theta}}_{0}^{2} (1\ensuremath{-}\frac{P}{{P}_{0}})$. In order to explain the shifts for the different fcc alloys of nickel with iron, use is made of a model where $\ensuremath{\gamma}$-iron is supposed to have two electronic levels and which gives account of many properties of these alloys at normal pressure.

Group-theoretical analysis of elementary particles in an external electromagnetic field

Abstract: We consider the symmetry properties of a particle interacting with an electromagnetic circularly polarized plane wave. The classical and quantum analysis of the stability group of the plane wave exhibits the origin of the mass shift of the particle. The Chakrabarti’s dynamical representation of the Poincare group is rederived and its physical meaning is given.

The Onset of Maternal Behavior in Rats, Hamsters, and Mice A Selective Review

Abstract: Publisher Summary This chapter discusses the onset of maternal behavior in rats, hamsters and mice, and explains the effects of gestation and parturition on the onset of maternal behavior. When maternal behavior is established in a naive animal by priming, the underlying mechanism seems different from that which occurs when it is established by gestation and parturition or by the administration of plasma or blood from a parturient female. First, the physiological correlates do not appear to be the same. Second, the serial order in which the different maternal activities occur differs. Finally, interactions with other types of possibly competitive behaviors— namely, exploration and aggression, present a different picture. Gestation and parturition coincide with numerous known endocrine changes, some of which could be involved in the onset of maternal behavior. Priming and gestation both involve a progressive decrease in preliminary exploration of pups before maternal activities occur. Infanticidal behavior may evolve differently. Repeated presentations of pups to naive infanticidal animals lead either to stereotyped killing or to the progressive onset of maternal behavior. During gestation, infanticides seem to decrease, at least, near to term. Interactions with territorial behavior are complex. High territorialism usually coincides with the absence of maternal behavior and with frequent infant-killing in males and in non-pregnant females.

Tectonic Significance of the Afar (or Danakil) Depression

Abstract: The Afar depression results from the separation of the Arabian and Nubian plates, with generation of new oceanic crust. Volcano-tectonic spreading axes form part of broad uplifted structures. The Gulf of Aden and Red Sea rifts constitute one and the same tectonic megastructure; but the distinct characteristics of the East African rift system suggest that it does not pertain to the megastructure.

Evolution of cell-mediated antitumor immunity in mice bearing a syngeneic chemically induced tumor. Influence of tumor growth, surgical removal and treatment with irradiated tumor cells.

Abstract: The evolution of the specific cell-mediated immune status was studied in C57BL/6 mice bearing a chemically induced syngeneic sarcoma, the TBL CL2 tumor. Peritoneal cells (PC) as the source of immunocompetent cells were repeatedly harvested from the same groups of mice checked in the in vitro colony growth inhibition tests (CGI) against target TBL CL2 cells. Confirming our data previously reported from studies with other tumor-host models, a characteristic evolution of the cell-mediated immune status was observed. Ten days after tumor inoculation, the PC from the tumor-bearing mice strongly inhibited the tumor target cells in the CGI test. This reactivity was, however, soon followed by an “eclipse” state of PC. This state continued, whenever checked, until the tumor-bearer's death. On the contrary, surgical removal of the tumor 6 weeks after inoculation led to a reappearance of PC reactivity within about 2 months. This period was clearly shortened in animals receiving a post-operative injection of irradiated cells of the TBL CL2 tumor. An in vivo study of tumor-graft rejection revealed a fair degree of parallelism with the CGI tests: the tumor graft was rejected in animals bearing the first tumor for 10 days and having activated PC; the tumor graft was not rejected in animals bearing huge tumors and having PC in the “eclipsed” state.

Reflectivities and Electronic Band Structures of CdTe and HgTe

Abstract: We have measured and calculated the reflectivity spectra of CdTe and HgTe. The measured and calculated reflectivities are compared and prominent features of the reflectivity spectra are identified with critical-point transitions in specific regions of the Brillouin zone. The symmetry and contribution to the reflectivity of important critical points are investigated. Empirical pseudopotential calculations of the band structure and the imaginary part of the frequency-dependent dielectric function, with spin-orbit effects included, are also presented.

Electroreflectance and Band Structure of Ga x In 1-x P Alloys

Abstract: The electroreflectance spectra of solution-grown ${\mathrm{Ga}}_{x}{\mathrm{In}}_{1\ensuremath{-}x}\mathrm{P}$ alloys were measured at room temperature in the whole range of composition. The variation of the ${E}_{0}$, ${E}_{1}$, ${E}_{0}^{\ensuremath{'}}$, and ${E}_{2}$ energies with concentration is reported: It is parabolic for ${E}_{0}$ and ${E}_{1}$, and approximately linear for ${E}_{0}^{\ensuremath{'}}$ and ${E}_{2}$. Except for ${E}_{1}$ these results agree with the calculation of the band structure by the dielectric two-band method in the virtual-crystal approximation including the effect of disorder. The latter effect is found small. For ${E}_{1}$ the deviation from a linear variation is larger than calculated. ${E}_{1}$ exhibits another interesting anomaly: Its spin-orbit splitting is maximum for $x=0.5$. The $\stackrel{\ensuremath{\rightarrow}}{\mathrm{k}}\ifmmode\cdot\else\textperiodcentered\fi{}\stackrel{\ensuremath{\rightarrow}}{\mathrm{p}}$ method is used to calculate some band parameters from our data. The $\ensuremath{\Gamma}\ensuremath{-}X$ conduction-band crossover energy ${E}_{c}$ and composition ${x}_{c}$ are accurately determined using the ${E}_{0}$ vs $x$ curve and the indirect gaps obtained from optical absorption. ${x}_{c}=0.63\ifmmode\pm\else\textpm\fi{}0.015$, ${E}_{c}=2.14\ifmmode\pm\else\textpm\fi{}0.01$ eV.

Use of a new detector for x-ray diffraction and kinetics of the ordering of the lipids in E. coli membranes and model systems.

Abstract: ALTHOUGH X-ray diffraction is the most powerful tool for the direct determination of structural parameters, long exposure times limit its use. Using a new detector we have been able to shorten the exposure times by several orders of magnitude, thus allowing study of unstable samples and of the kinetics of structural transitions. We have applied this technique to biological membranes and model systems.

Spectres d'absorption dans l'ultraviolet lointain de Be, B, C, N, Mg, Al ET Si

Abstract: Resume Une technique originale de spectroscopie d'absorption mise au point en 1968 a permis l'observation de structures situees dans le continu de photoionisation d'elements legers (Be, B, C, N, Mg, Al, Si). La methode fait appel a deux etincelles sous vide, l'une etant utilisee comme source de spectre continu, l'autre produisant le milieu absorbant. On presente ici les resultats obtenus grâce aux ameliorations apportees a cette technique. Soixante quinze nouvelles transitions correspondant a des niveaux a grande probabilite d'autoionisation ont ete identifiees. Il s'agit d'excitation electronique double, ou simple lorsque l'electron appartient a une sous-couche ou a une couche interne.

Photochemical reactions of aromatic ketones with nucleic acids and their components. I. Purine and pyrimidine bases and nucleosides.

Abstract: — The photochemical reactions of benzophenone and acetophenone with purine and pyrimidine derivatives in aqueous solutions have been investigated by flash photolysis and steady-state experiments. Upon excitation of these two ketones in aqueous solutions, two transient species are observed: molecules in their triplet state and ketyl radicals. The triplet state lifetimes are 65 μsec for benzophenone and 125 μsec for acetophenone. The ketyl radicals disappear by a second order reaction, controlled by diffusion. In the presence of pyrimidine derivatives, the triplet state is quenched and the ketyl radical concentration is decreased without any change in its kinetics of disappearance. Ketone molecules in their triplet state react with purine derivatives leading to an increase in the yield of ketyl radicals due to H-atom abstraction from the purines. Steady-state experiments show that benzophenone and acetophenone irradiated in aqueous solution at wavelengths longer than 290 nm undergo photochemical reactions. The rate of these photochemical reactions is increased in the presence of pyrimidine derivatives and even more in the presence of purine derivatives. Following energy transfer from the triplet state of benzophenone to diketopyrimidines, cyclobutane dimers are formed. The energy transfer rate decreases in the order orotic acid > thymine > uracil. Benzophenone molecules in their triplet state can also react chemically with pyrimidine derivatives to give addition photoproducts. All these results are discussed with respect to photosensitized reactions in nucleic acids involving ketones as sensitizers.

Heat-Flow Microcalorimetry and Its Application to Heterogeneous Catalysis

Abstract: Publisher Summary This chapter reviews heat-flow calorimetry as a new tool in adsorption and heterogeneous catalysis research. Heat-flow calorimeters are adapted to the investigation (1) of slow adsorption or reaction processes, (2) at moderate or high temperatures, and (3) on solids that present a poor thermal diffusivity. Heat-flow calorimetry allows the study of adsorption or reaction processes that cannot be studied conveniently with the usual adiabatic or pseudoadiabatic, adsorption calorimeters. The chapter describes the general principles of heat-flow calorimetry, the specific advantages of heat-flow microcalorimeters for the determination of heats of adsorption. It illustrates the use of this calorimetric technique in the study of heterogeneous catalysis reactions. All heat-flow microcalorimeters described in the chapter have been applied to the study of gas–solid interactions. In heat-flow calorimeters, it is important that the heat sink remain, throughout the experiment, at a constant temperature.