Showing papers by "University of Mons published in 1994"

A Unified Description of Linear and Nonlinear Polarization in Organic Polymethine Dyes

Abstract: An internal or external electric field F can drive the chemical structure, bond order alternation, and electronic structure of linear polymethine dyes from a neutral, bond-alternated, polyene-like structure, through a cyanine-like structure, and ultimately to a zwitterionic (charge-separated) bond-alternated structure. As the structure evolves under the influence of F, the linear polarizability α, the first hyperpolarizability β, and the second hyperpolarizability γ are seen to be derivatives, with respect to F, of their next lower order polarization (for α) or polarizability (for β and γ). These derivative relations provide a unified picture of the dependence of the polarizability and hyperpolarizabilities on the structure in linear polymethine dyes. In addition, they allow for predictions of structure-property relations of higher order hyperpolarizabilities.

Diquonia and potential models

Abstract: We present four new quark-quark potentials, developed in the framework of the nonrelativistic quark model (NRQM), which can reproduce quite well the spectra of mesons and baryons. They contain a central part which is of type “Coulomb+linear” or “Coulomb +2/3-power”, and a strong but smooth hyperfine term. With these four potentials and the one proposed by Bhaduri et al., we have calculated masses and decay properties of some interesting diquonia (q2q−2 mesons). We have not found appreciable difference between the results of the five potentials considered, indicating that the properties of diquonia are, to a large extent, potential-independent in the NRQM.

Effect of muscimol microinjections into the prepositus hypoglossi and the medial vestibular nuclei on cat eye movements

Abstract: 1 For horizontal eye movements, previous observations led to the hypothesis that the legendary neural integrator necessary for correct gaze holding, adequate vestibuloocular reflex (VOR), and optokinetic nystagmus, was located in the region of the complex formed by the nucleus prepositus hypoglossi (NPH) and the medial vestibular nucleus (MVN) 2 The aim of the present study was to test the respective contributions of the NPH, of the rostral part of the MVN, which contains most second-order vestibular neurons, and of the central part of the MVN to the horizontal integrator 3 An injection of muscimol was used to inactivate each of these three zones in the cat's brain Muscimol is a gamma-aminobutyric acid (GABA) agonist By binding to GABAA receptors, it induces a hyperpolarization of the neurons that nullifies their activity Muscimol was injected into the brain stem of the alert cat through a micropipette by an air pressure system 4 The search coil technique was used to record spontaneous eye movements and the VOR induced by rotating a turntable at a constant velocity VOR was analyzed by a new method: transient analysis of vestibular nystagmus 5 A unilateral injection of muscimol into the NPH induced a bilateral gaze-holding failure: saccades were followed by a centripetal postsaccadic drift A vestibular imbalance was also present but it was moderate and variable The VOR responses were distorted drastically Through transient analysis of vestibular nystagmus, that distortion was revealed to be due more to a failure of the neural integrator than to an alteration of the vestibular input to the neural integrator The responses to a rotation either toward the injected side or in the opposite direction were asymmetrical The direction of that asymmetry was variable 6 A unilateral injection of muscimol into the rostral part of the MVN caused a vestibular imbalance: in complete darkness, a nystagmus appeared, whose linear slow phases were directed toward the side of injection 7 A unilateral injection of muscimol into the central part of the MVN induced a syndrome where a severe bilateral gaze-holding failure was combined with a vestibular imbalance In the light, saccades were followed by a bilateral centripetal postsaccadic drift In complete darkness, a nystagmus was observed, whose curved slow phases were directed towards the side of injection The VOR responses were distorted drastically Here again, that distortion was revealed by our analysis to be due more to a failure of the neural integrator than to an alteration of the vestibular input to the neural integrator(ABSTRACT TRUNCATED AT 400 WORDS)

Cerebellar hypermetria is larger when the inertial load is artificially increased

Abstract: Hypermetria is a classical cerebellar symptom designating the overshoot observed when a patient is asked to make a very fast and accurate movement. The movement studied here was wrist flexion. Hypermetria was found to be increased by artificially increasing the inertia of the moving hand. A normal subject adapted himself to increasing inertia by increasing both his agonist activity (the launching force) and its antagonist activity (the braking force). In the same circumstances, a patient with symptoms of cerebellar system dysfunction was found to be able to increase his agonist activity but not his antagonist activity.

Spin asymmetry in muon-proton deep inelastic scattering on a transversely-polarized target

Abstract: The anatomy of the hyo-lingual apparatus in the iguanid lizard Oplurus cuvieri has been studied by light microscopy and scanning electron microscopy. Four areas were observed on the dorsal lingual epithelium of the lizard. Tongue tips are covered with a smooth epithelium. Closely packed flattened and cylindriform papillae cover the foretongue. The surface of the midtongue bears an unpapillose epithelium. Short conical papillae are arranged on the two lateral posterior bundles of the tongue. At high magnification, microvilli and microridges are widely distributed over the surface of the papillae. The epithelium of the papillae is composed of cells filled with secretory granules. Each surface plays successive roles during food ingestion, intra-buccal transport, and swallowing. The mucous interpapillary spaces would serve the adherence between the tongue and the food, the smooth epithelium of the midtongue should facilitate movements of the prey toward the pharynx, and conical papillae of the hindtongue present a rough surface which should act on the prey during the swallowing phase. The intrinsic morphology of the tongue is rather similar to that previously described for iguanids, but fibers of M. verticalis encircles ventrally the lingual process. These fibers could act in tongue protrusion as previously suggested for agamids. The morphology and function of the extrinsic tongue musculature and the hyoid musculature, analysed by electrical stimulations, are similar to the previous descriptions in iguanids and agamids either for feeding or displaying functions.

Tongue structure and function in Oplurus cuvieri (reptilia: Iguanidae)

Abstract: The anatomy of the hyo-lingual apparatus in the iguanid lizard Oplurus cuvieri has been studied by light microscopy and scanning electron microscopy. Four areas were observed on the dorsal lingual epithelium of the lizard. Tongue tips are covered with a smooth epithelium. Closely packed flattened and cylindriform papillae cover the foretongue. The surface of the midtongue bears an unpapillose epithelium. Short conical papillae are arranged on the two lateral posterior bundles of the tongue. At high magnification, microvilli and microridges are widely distributed over the surface of the papillae. The epithelium of the papillae is composed of cells filled with secretory granules. Each surface plays successive roles during food ingestion, intra-buccal transport, and swallowing. The mucous interpapillary spaces would serve the adherence between the tongue and the food, the smooth epithelium of the midtongue should facilitate movements of the prey toward the pharynx, and conical papillae of the hindtongue present a rough surface which should act on the prey during the swallowing phase. The intrinsic morphology of the tongue is rather similar to that previously described for iguanids, but fibers of M. verticalis encircles ventrally the lingual process. These fibers could act in tongue protrusion as previously suggested for agamids. The morphology and function of the extrinsic tongue musculature and the hyoid musculature, analysed by electrical stimulations, are similar to the previous descriptions in iguanids and agamids either for feeding or displaying functions.

Chemical and electronic aspects of metal/conjugated polymer interfaces. implications for electronic devices

Abstract: The chemical nature and the electronic structure of metal/conjugated polymer interfaces are investigated in the context of polymer-based light-emitting diodes. We consider the interaction of low-workfunction metals (Al, Ca) with the surface of conjugated polymers or model oligomer molecules with a combined experimental and theoretical approach. The early stages of the interface formation are followed with X-ray and ultraviolet photoelectron spectroscopies and the experimental data are compared to the results of quantum chemical calculations. The reactions of Al and Ca with the organic surface are found to be fundamentally different: while the former forms new covalent bonds onto the polymer backbone, the latter tends to dope the conjugated system. Both types of reaction are expected to modify drastically the electronic properties of the polymer semiconductor.

Performance of MSGC on electronically and ionically conductive substrata in various operational conditions

Abstract: Recent measurements realized with Microstrip Gas Chambers (MSGC) manufactured on glass substrata in a range of bulk resistivity are presented. Chambers made on electronically conductive supports with resistivity of 10 9 ω cm and gold strips show a stable behaviour during long term irradiation up to an accumulated charge of 130 mC/cm of strip when operated in an argon-dimethylether (DME) mixture. Similar measurements realised with argon-methane show instead a fast degradation of gain already at collected charge of around 5 mC/cm. Further investigation of MSGC performance with different Ar-DME compositions show that the larger stable gain can be achieved with a 50-50 mixture. We present also results of beam runs performed with MSGC manufactured on Hoya SL glass with an anode to cathode distance of 200 μm and a 2 mm gas layer. The dependence of efficiency and spatial resolution on the incidence angle of track was measured with argon-DME and xenon-DME gas mixtures; for minimum ionizing particles perpendicular to the chambers (0°) the spatial resolution for Xe gas mixture is 65 μm rms and the efficiency 98%. For incidence angles up to 10° a small degradation of both parameters was observed.

Improved experimental and theoretical energy levels of neon I

Abstract: The spectrum of neutral neon used as a carrier gas has been measured by the Fourier transform spectroscopy technique from 1800 to 9000 cm−1. We report on transitions leading to improved energy levels for the 4f, 5f, 6f, 7f and the 5g configurations. In addition, we identify transitions leading to the previously unknown 6g and 7g configurations. Theoretically, we have generalized the polarization and pair coupling formulae to the extended quadrupole-polarization model. Explicitly accounting for the 6f'-7f (6g'-7g) quadrupole interaction, our two-parameter expression reproduces 18 observed levels (ng) with a mean deviation of 0.016 cm−1. Inclusion of the 24 observed pairs of nf levels increases the mean deviation to 0.036 cm−1.

Axially symmetric solutions in electroweak theory.

Abstract: We present the general ansatz, the energy density, and the Chern-Simons charge for static axially symmetric configurations in the bosonic sector of the electroweak theory. Containing the sphaleron, the multisphalerons, and the sphaleron-antisphaleron pair at finite mixing angle, the ansatz further allows the construction of the sphaleron and multisphaleron barriers and of the bisphalerons at finite mixing angle. We conjecture that further solutions exist.

Measurement of the polarisation of a high energy muon beam

Abstract: A muon beam polarimeter has been built for the SMC experiment at the CERN SPS, for muon energies of 100 to 200 GeV. The beam polarisation is determined from the energy spectrum of positrons from the decay μ + → e + ν c ν μ . A polarisation of − 0.82 is measured with a relative systematic accuracy of 3%.

The ring imaging Cherenkov detector of DELPHI

Abstract: The ring imaging Cherenkov detector system in the DELPHI experiment at the Large Electron-Positron storage ring at CERN, is designed to do particle identification over most of the solid angle in the momentum range from ∼2 GeV c to ∼40 sol GeV c . Two radiator media are used to cover the momentum range; (i) a 1 cm layer of liquid C6F14, and (ii) a volume filled with gaseous C5F12 or C4F10. Photosensitive time projection chambers record the conversion points of the ultraviolet photons produced in both radiator systems. The total active area is ∼30 m2 in the barrel region and ∼8 m2 in the two endcaps. The design of the detector systems is described in this paper. We will also report performance figures and compare them to simulation studies.