Showing papers by "École Normale Supérieure published in 1975"

Extended Particles in Quantum Field Theories

Abstract: The method of collective coordinates developed in the study of strong-coupling theory is used for the quantization of the kink solution of a two-dimensional nonlinear field theory. The position of the kink is treated as a collective coordinate, which represents the position of a particle. It is separated from the rest of the coordinates, which represent the internal degrees of freedom of an extended particle. Two similar but different methods are presented; the one is nonrelativistic and suited for the weak-coupling limit, while the other is relativistic.

Parity violation induced by weak neutral currents in atomic physics. part II

Abstract: The first part of this paper gives a detailed account of the evaluation of the electric dipole amplitude induced in alkali one-photon S-S transitions, by the parity violating electron-nucleus short range potential Vp.v. associated with the weak neutral currents. Two methods are presented : the first involves an explicit sum over the contributions of the P-states admixed with the S-states and incorporates the best information available on S-P electric dipole amplitudes. The second method, mathematically more elegant, avoids with the help of Green's function techniques any explicit sum over the P states, and, provided that some spin-orbit corrections are neglected, leads to a fairly simple formula involving Coulomb integrals tabulated in the literature and the interpolated quantum defects for S and P waves. The second part is devoted to a description of possible ways to detect parity violation induced in radiative S-S transitions, with a brief discussion of physical processes which could be a source of experimental difficulty. The last section of the paper deals with a theoretical analysis of the influence of a static electric field on the radiative S-S transitions. An evaluation of the induced electric dipole amplitude in the case of cesium indicates that it will compete with the magnetic dipole amplitude for electric fields larger than 10 V/cm. An interference effect between these two amplitudes gives rise to an electronic polarization in the final atomic state proportional to the vector product of the static electric field by the photon momentum which, in a typical case, could be as large as 64 %; the measurement of this interesting and rather peculiar effect will lead to a determination of the sign of the magnetic dipole amplitude. Moreover parity violation could manifest itself by a dependence of this electron polarization on the state of circular polarization of the incident photon.

Perturbation expansion around extended-particle states in quantum field theory

Abstract: The quantum mechanics of solitary-wave classical solutions of nonlinear wave equations is discussed in detail for the kink solution of two-dimensional φ4 field theory. The formalism provides a natural interpretation of an extended particle, the soliton, for the classical kink. The perturbation theory around the extended particle is developed and used to calculate the radiative corrections for the mass of soliton up to one loop. The mass renormalization is discussed in detail to show that the mass counterterm to the nonsoliton sector also does the job for the present case, i.e. one-soliton sector. Although our formalism is not manifestly Lorentz-covariant, the Lorentz covariance is shown explicitly by calculating the soliton energy for a fixed momentum. Finally, the paper also contains the perturbation calculation of matrix element of φ fields between one-soliton states.

Mechanics of steady spinning of a viscoelastic liquid

Abstract: The equations for steady isothermal spinning of a viscoelastic liquid are solved for a fluid model with constant modulus and a single constant relaxation time. High stress levels are predicted for elastic liquids, and the velocity approaches a linear profile in the limit of maximum drawdown. These predictions are in accordance with the observed behavior of polymeric liquids in isothermal spinning. Relaxation times computed from spinning data of Spearot and Metzner and Acierno et al. for four low density polyethylene melts are comparable to those measured rheogoniometrically, though the spinning relaxation times are 20 to 80% larger.

Production of gaseous pore pressure during rock slides

Abstract: When a rock mass slips, the local heating of the slip surface transforms pore water into vapour if the surface of failure is deep enough. It is possible to calculate, as a first approximation, a critical displacement of the mass necessary to create vapour in the slide zone. A second approximation gives the relation between critical displacement and rate of shear displacement as the slide mass creeps towards catastrophe.

Interfacial dislocation networks around γ′ precipitates in nickel-base alloys

Abstract: The three-dimensional dislocation network covering the γ–γ′ interface in a nickel-base superalloy was observed and identified by transmission electron microscopy Estimates of the lattice misfit yielded about – 0·3% in the alloy considered Assuming all dislocations to be of pure edge character the complete network could be analysed as formed by a/2〈110〉 dislocation loops extending over a tetrakaiUdecahedron: the eight {111} faces are covered with hexagonal dislocation networks, while the six {001} faces exhibit square and octagonal dislocation arrangements resulting from the interaction of dislocations with orthogonal Burgers vectors The importance of interfacial dislocation networks and the role of the lattice misfit in oriented γ′ coalescence during creep are pointed out

Linear quadratic optimal estimation and control with receding horizon

Abstract: Implementation of linear quadratic optimal regulators and Kalman estimators is not straightforward where industrial process control is concerned. This is mainly due to the requirement that many parameters (Q and R matrices, spectral-density matrices) having no direct physical meaning must be chosen a priori. The letter contains simplified optimal algorithms that lead to stationary gains, given by explicit expressions.

Immuno-fluorescent reactivity to anti-somatostatin in the gastro-intestinal mucosa of the dog.

Abstract: Evidence is presented that somatostatin-containing cells are present in the gastro-intestinal tract of the dog. Thus immuno-fluorescent cells were detected by the use of antiserum to cyclic somatostatin. These cells were mainly encountered in the antral mucosa and in the neighbourhood of gastrin-producing cells. No cross reaction was observed between gastrin and somatostatin. It is suggested that locally produced somatostatin controls gastrin secretion, and, more generally, that somatostatin-containing cells, multifocally distributed, modulates secretion of a large number of glands.

Dynamics of macromolecular chains. II. Orientation relaxation generated by elementary three-bond motions and notion of an independent kinetic segment

Abstract: In the preceding paper, general equations were established for the motions of chains confined to a tetrahedral lattice. In the present paper, bond orientation correlation and autocorrelation functions are explicitly calculated for the case where only three-bond elementary motions are considered. Effects due to the chain end are analyzed and the relaxation time distribution function is established. The expressions obtained reflect the influence of the chain structure. Finally, to characterize the dynamic behavior of chains in orientation relaxation experiments, the notion of an independent kinetic segment is proposed.

Correspondence factor analysis: An outline of its method

Abstract: Correspondence factor analysis is a multivariate technique that may be applied to any type of data and to any number of data points. It detects associations and oppositions existing between subjects and objects, measuring their contribution to the total inertia for each factor. The probabilistic character of the data matrix is taken into consideration, and together with the principle of distributional equivalence, results in stability. The projection of the subjects and the objects onto the same set of factorial axes enables two-dimensional graphs to be drawn which offer aid in the interpretation of the results.

A Comparison of Linear and Nonlinear Evaluation Process Models

Abstract: The findings of a comparative analysis of linear and nonlinear evaluation process models using 3 (number of models) × 3 (levels of number of attributes) × 2 (levels of “acceptability” of alternativ...

Band structure and Fermi surface of hcp ferromagnetic cobalt

Abstract: A Korringa-Kohn-Rostoker first-principles computation of the band structure of ferromagnetic hcp cobalt is reported A muffin-tin potential and a Kohn-Sham exhange-correlation potential were used in conjunction with a rigid exchange splitting Twelve energy bands in $\frac{1}{24\mathrm{th}}$ of the hcp Brillouin zone were calculated as well as the density of states and the Fermi surface The exchange splitting was found to be 139 eV and a total density of states at the Fermi level of 1561 electrons/(atom Ry) The spin-orbit coupling constant ${\ensuremath{\xi}}_{3d}$ has been computed and is equal to 6 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ Ry The essential features of the band structure agreed with the requirements of the itinerant-electron model of ferromagnetism of the Stoner-Wohlfarth theory Our resulting density of states was able to explain the available photoemission data The calculated Fermi surface is in good agreement with the de Haas-van Alphen experiments, particularly for the neck of the point $\ensuremath{\Gamma}$ in the spin-up Fermi surface The spin-orbit interaction has been taken into account in a qualitative way in order to explain the orbits around $L$ in the spin-down Fermi surface A comparison with the existing experimental data has permitted us to estimate the mass enhancement due to many-body effects at the $\ensuremath{\Gamma}$ neck as 104, resulting in a value of 081 for the electron-magnon contribution

Late sodium current in the node of Ranvier.

Abstract: Voltage clamp experiments carried out on nodes of Ranvier of myelinated fibres ofRana esculenta showed that a small fraction of sodium channels fail to inactivate Thus during long lasting depolarizing pulses there is a small Na-current superimposed on the leakage and potassium currents This late Na-current appears more marked in sensory fibres than in motor ones

Backscattering study and theoretical investigation of planar channeling processes. I. Experimental results

Abstract: Backscattering experiments in planar channeling have been performed on iron single crystals with 1.9-MeV $^{4}\mathrm{He}$ beams; these conditions having been chosen for optimal study of the structure of the spectra. Both for the (110) and (100) planes five equally spaced yield maxima are clearly resolved, the maxima damping out at lower energies. Spectra were also registered at various angles of incidence ${\ensuremath{\phi}}_{0}$ with respect to the planes. Yield maxima are observed up to values of ${\ensuremath{\phi}}_{0}$ twice the half-width at half-minimum ${\ensuremath{\psi}}_{\frac{1}{2}}$ of an angular scan across the plane [${\ensuremath{\psi}}_{\frac{1}{2}}={18}^{\ensuremath{'}}$ for the (110) plane]. Except for the first two peaks, these maxima have the same spacing as in the aligned spectrum. They appear to be due to particles belonging to a well-defined transverse energy interval. The mean stopping power for these particles is close to the random stopping power and the mean half-wavelength of their oscillating trajectories in the planar channels calculated from the results is $\ensuremath{\lambda}=380$ \AA{} for the (110) plane and $\ensuremath{\lambda}=320$ \AA{} for the (100) plane. For ${\ensuremath{\phi}}_{0}g1.2{\ensuremath{\psi}}_{\frac{1}{2}}$, the yield on the first maximum is greater than the random yield, reaching \ensuremath{\sim}1.6 times the latter for $1.4{\ensuremath{\psi}}_{\frac{1}{2}}l{\ensuremath{\phi}}_{0}l1.8{\ensuremath{\psi}}_{\frac{1}{2}}$. The shoulder effect in the angular scans, as observed for various depths, is clearly related to the yield maxima and hence depends strongly on the position and width of the depth interval chosen. The meaning and validity of the assumption of statistical equilibrium for planar channeled particles are discussed in light of the results.

α- andβ-ecdysone levels in insect haemolymph: Correlation with developmental events

Abstract: Les taux d'α-et de β-ecdysone ont ete determines dans l'hemolymphe dePieris brassicae au cours du dernier stade larvaire et de la metamorphose. Parallelement, les taux de synthese d'ADN, d'ARN et de proteines ont ete mesures dans les ebauches alaires. La comparaison de ces donnees a ete discutee en fonction du mode d'action possible des deux hormones.

The Significance of Chromosomal Studies in the Systematics of the Malagasy Lemurs

Abstract: Chromosomal studies of the Malagasy lemurs have been particularly fruitful in two areas of investigation where these animals pose various difficult problems: systematics and evolution. In this chapter, we will report on the significance of cytogenetics in the systematics of the lemurs.