Showing papers by "University of Mons published in 1989"
TL;DR: Pernigraniline is shown to accomodate elementary excitations of soliton and polaron types having remarkable properties, in some instances markedly different from those predicted for the so-called AB polymer.
Abstract: The electronic structure of fully oxidized polyaniline, pernigraniline, is investigated in the framework of the Su-Schrieffer-Heeger Hamiltonian, making use of an original renormalization technique. Among the family of polyanilines, pernigraniline is the only form to possess a degenerate ground state. It is shown to accomodate elementary excitations of soliton and polaron types having remarkable properties, in some instances markedly different from those predicted for the so-called AB polymer. Nonlinear optical properties of the material are expected to be important.
80 citations
TL;DR: In this article, the optical properties of polyemeraldine base (PEB) were studied using the semi-empirical INDO/S-CI method and the theoretically calculated optical absorption spectrum is in very good agreement with experimental results showing absorption peaks at ∼2 and ∼4 eV.
46 citations
TL;DR: In this paper, a detailed investigation of energy levels and radiative transition probabilities is presented for the n = 4, Δn = 0 transitions of the ions Rb VIII to Xe XXV along the zinc isoelectronic sequence.
Abstract: A detailed investigation of energy levels and radiative transition probabilities is presented for the n = 4, Δn = 0 transitions of the ions Rb VIII to Xe XXV along the zinc isoelectronic sequence. The Relativistic Hartree-Fock method is applied for the calculations combined with Slater parameter optimization procedures. Comparisons with multiconfigurational Dirac-Fock calculations show that the most important relativistic effects are taken into account.
34 citations
TL;DR: In this paper, a critical evaluation of the classical kinetic theory of polymer crystallization is presented, concluding that even the most recent version of Hoffman and Miller's theory does not explain the kinetic data of Labaig2 on crystallization of polyethylene (PE) from the melt.
34 citations
TL;DR: Cloning the corresponding fully-coding cDNA from HTC cells suggests that the lack of associated FBPase-2 activity in HTC cells results from a post-translational modification of the enzyme rather than from the difference in amino acid sequence.
Abstract: In liver, the 470-residue bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2) catalyses the synthesis and degradation of fructose 2,6-bisphosphate, a potent stimulator of glycolysis. In rat hepatoma (HTC) cells, this enzyme has kinetic, antigenic, and regulatory properties, such as insensitivity to cyclic AMP-dependent protein kinase and lack of associated FBPase-2 activity, that differ from those in liver. To compare the sequence of the HTC enzyme with that of the liver enzyme, we have cloned the corresponding fully-coding cDNA from HTC cells. This cDNA predicts a protein of 448 residues in which the first 32 residues of liver PFK-2/FBPase-2 including the cyclic AMP target sequence have been replaced by a unique N-terminal decapeptide. The rest of the protein is identical with the liver enzyme. An N-terminally truncated recombinant peptide of 380 residues containing the PFK-2 and FBPase-2 domains was expressed in Escherichia coli as a beta-galactosidase fusion protein. It was recognized by anti-PFK-2 antibodies but its enzymic activities were barely detectable. In contrast, a cDNA fully-coding for the HTC enzyme could be expressed in E. coli as a beta-galactosidase-free peptide that exhibited both PFK-2 and FBPase-2 activities. This peptide had those PFK-2 kinetic properties of the HTC enzyme that differ from the liver enzyme. These data, together with immunoblot experiments, suggest that the lack of associated FBPase-2 activity in HTC cells results from a post-translational modification of the enzyme rather than from the difference in amino acid sequence. As well as this peculiar type of PFK-2/FBPase-2 mRNA, HTC cells also contained low concentrations of the liver-type mRNA. Unlike in liver, neither mRNA was induced by dexamethasone in these cells.
29 citations
TL;DR: An additional relaxation pathway via the myelin lipids, which are not directly visible to medical NMR due to their fast T2 decay, is proposed and relaxation dispersion data are successfully analyzed on the basis of this model.
Abstract: Human brain white matter exhibits an uncommonly strong dispersion of 1/T1 at high fields. An additional relaxation pathway via the myelin lipids, which are not directly visible to medical NMR due to their fast T2 decay, is proposed. Relaxation dispersion data are successfully analyzed on the basis of this model. © 1989 Academic Press, Inc.
28 citations
TL;DR: In this paper, a series of thiophene-based conjugated polymers built from monomers with extended π-electron delocalization are investigated and compared with theoretical parameters such as bandgaps and bandwidths.
Abstract: We investigate a series of thiophene-based conjugated polymers built from monomers with extended π-electron delocalization. The polymers are polythiophene, polythieno[3,2-b]thiophene and polydithieno[3,2-b;2',3'-d]thiophene. In order to obtain a better understanding of the evolution of the transport properties in this family of compounds, we present spectroscopic studies, including infrared, UV-visible and emission data, structural investigations and conductivity measurements, and compare them with theoretical parameter such as bandgaps and bandwidths as calculated by the Valence Effective Hamiltonian method. Polymer growth is optimized to prevent at best morphological differences between the three polymers.
24 citations
TL;DR: Geometry optimizations and band structure calculations are reported on two polymeric vinylene derivatives of pyrene: poly(1,6) and poly(2,7) vinylene as mentioned in this paper.
Abstract: Geometry optimizations and band structure calculations are reported on two polymeric vinylene derivatives of pyrene: poly(1,6‐pyrenylene vinylene) and poly(2,7‐pyrenylene vinylene). The results are indicative of a dramatic sensitivity of the electronic structure on the mode of connection of the two vinylene units to the pyrene rings, in agreement with the chemist’s intuition. An analysis of the atomic π orbital contributions to the one‐electron wave functions shows that the HOMO–LUMO characteristics of both compounds are markedly different. The 1‐6 mode of connection leads to an electronic structure similar to that of polyparaphenylene with a bandgap of 2.9 eV. The 2‐7 mode of connection results in a significantly lower bandgap, around 1.7 eV, due to the stabilization of quinoid resonance structures.
24 citations
TL;DR: After deep freezing of tissue samples on dry ice, no significant changes in 1/T1 over the whole frequency range could be observed for brain tissue, whereas for muscle and liver tissue characteristic alterations were detected.
Abstract: Knowledge about the dependence of NMR parameters of excised tissues on time and storage conditions is important for correct interpretation of in vivo clinical results based upon in vitro measurements which in many cases are easier to perform. Literature data on this topic are scarce and sometimes contradictory. In this study, we investigated the change of the proton longitudinal relaxation rate (1/T1) of freshly excised rat tissues with storage conditions over a wide range of proton Larmor frequencies (0.01-50 MHz). Special interest was paid to long-term storage in the deep frozen state. After deep freezing of tissue samples on dry ice, no significant changes in 1/T1 over the whole frequency range could be observed for brain tissue, whereas for muscle and liver tissue characteristic alterations were detected. We conclude that for normal brain tissue this storage procedure is suitable for the prediction of in vivo 1/T1 results from in vitro studies. © 1989 Academic Press, Inc.
21 citations
TL;DR: An experimental study of free convection in binary mixtures when convection is theoretically predicted to appear in the form of rolls of large extent and quantitative measurements of the very slow velocities associated with this convective pattern are presented.
Abstract: We present an experimental study of free convection in binary mixtures when convection is theoretically predicted to appear in the form of rolls of large extent. Quantitative measurements of the very slow velocities associated with this convective pattern are presented.
21 citations
TL;DR: In this article, the electronic properties of three types of conducting polymers: trans-polyacetylene (proto-typical of systems with a degenerate ground state), polythiophene (as an example of compounds with a non-degenerate ground states), and polyemeraldine (which can be doped via protonation) are reviewed.
Abstract: The electronic properties of three types of conducting polymers: trans -polyacetylene (proto-typical of systems with a degenerate ground state), polythiophene (as an example of compounds with a nondegenerate ground state), and polyemeraldine (which can be doped via protonation) are reviewed. The structural and electronic band structure properties of these systems are studied at various defect concentrations corresponding to undoped, lightly doped, and highly doped polymers. Geometry optimizations of oligomeric equivalents to the undoped and doped polymers are performed using the semi-empirical MNDO and AM1 methods. The electronic band structures are calculated using the VEH method. The interpretation of the optical absorption data is discussed in terms of interband transitions; for doped trans -polyacetylene including soliton defects and for doped polythiophene including bipolaron defects. For highly doped trans -polyacetylene and polythiophene as well as for protonated polyemeraldine, the electronic structure of a polaron lattice conformation is discussed and shown to be in agreement with existing optical and magnetic data on these polymers.
TL;DR: In this article, the authors present a description of the valence electronic structure of the metal-free porphine macrocycle, which is used to interpret the gas-phase and solid-state UPS spectra.
TL;DR: In this paper, the authors studied the production of vector mesons (charged ρ(770), ω(783), ϕ(1020), and neutralK*(892)) in π−p interactions at 360 GeV/c.
Abstract: The inclusive production of vector mesons (charged ρ(770), ω(783), ϕ(1020) and neutralK*(892)) in π−p interactions at 360 GeV/c is studied. The data are based on 160 000 reconstructed events recorded in the NA 27 Experiment using the LEBC-EHS facility at CERN. The production cross sections in the forward hemisphere in c.m.s. and the longitudinal momentum distributions are determined. The results are compared with data obtained at lower energies.
TL;DR: In this article, a comparison between the experimental UPS spectrum of polystyrene and a theoretically simulated spectrum derived from valence effective Hamiltonian (VEH) calculations is made, based on a stereoregular helical isotactic poly styrene chain where the bonds joining the backbone to the phenyl groups are trans relative to the backbone.
TL;DR: The eye movements evoked by microstimulations in the medulla of 9 alert cats were mapped to show that regardless of the initial position of the gaze (to the left as well as to the right), microstimulation given at the same place induced a movement of both eyes toward their neutral position.
Abstract: This study maps the eye movements evoked by microstimulations in the medulla of 9 alert cats. Trains of square waves (20 microA amplitude, 0.2 msec duration, 200 Hz) were delivered through glass-covered tungsten microelectrodes (0.5-1 M omega). Movements of both eyes were recorded by the magnetic field/eye coil technique. Stimulation of the prepositus hypoglossi nucleus (PH) evoked nystagmus with ipsilaterally-directed slow phases followed by after-nystagmus with contralaterally-directed slow phases. Stimulation of the medial vestibular nucleus (MVN) induced nystagmus whose slow phases were more often ipsilaterally-directed but at time contralaterally-directed. At nearly all sites where we stimulated the reticular formation underlying prepositus and vestibular nuclei (from P4.5 to P12), we recorded versional conjugate movements. They were most often ipsilaterally-directed. Some microstimulations in the region of the medial longitudinal fasciculus evoked recentering eye movements: regardless of the initial position of the gaze (to the left as well as to the right), microstimulations given at the same place induced a movement of both eyes toward their neutral position. The amplitude of this movement was proportional to the eccentricity of the pre-stimulation position of the gaze.
TL;DR: In this paper, a non-empirical valence-effective Hamiltonian (VEH) investigation of the electronic properties of a model system for cyano-(phthalocyaninato)cobalt(III) (PcCoCN) crystal is presented.
TL;DR: Les derives toxiques contenus dans la glande a venin de la fourmi ont un squelette du type perhydro pyrido [1,2-c] pyrrolo [1',2'-a] pyrimidine as discussed by the authors.
Abstract: Les derives toxiques contenus dans la glande a venin de la fourmi ont un squelette du type perhydro pyrido [1,2-c] pyrrolo [1',2'-a] pyrimidine
TL;DR: In this paper, multi-skyrmion solutions of the Weinberg-Salam model are investigated in relation with the "hadroid" present in the Sakurai model of vector mesons.
Abstract: We investigate multi-skyrmion solutions of the Weinberg-Salam model. They are put in relation with the “hadroid” present in the Sakurai model of vector mesons.
TL;DR: In this article, the synthesis of thin films of CuxTey compounds on glass is performed under CW Ar+ laser irradiation, and the variation of temperature with time is measured by an interferometric method.
TL;DR: In this article, it was shown that ∥ T α f ∥ q, u ≦ C ∥grad f ∈ p, v' q > n / α holds.
Abstract: Let then, for certain weight functions u and v and indices p , q , it is shown that ∥ T α f ∥ q, u ≦ C ∥grad f ∥ p, v' q > n / α holds. For α=l, p = q and u = v ≡ l this reduces to a result of M. Weiss. In addition we establish n -dimensional weighted Hardy—Littlewood type inequalities ofthe form for large classes of weights.
TL;DR: In this article, a Wolff-type ring contraction was used to give cyclopentadienylidene methanimine ions which undergo an internal oxidation process producing ionized cyclopENTADienone.
Abstract: 1-(2-nitrophenyl)benzotriazole loses nitrogen upon electron ionization. This reaction is followed by a Wolff-type ring contraction to give cyclopentadienylidene methanimine ions which undergo an internal oxidation process producing ionized cyclopentadienone.
01 Jan 1989-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the output count rate for a Poisson process after a series arrangement of two dead times, where each of them is either of the extended or of the nonextended type, are reversed analytically.
Abstract: The formulae which give the output count rate for a Poisson process after a series arrangement of two dead times, where each of them is either of the extended or of the nonextended type, are reversed analytically. For each arrangement a series is written which yields the two possible input count rates; an application is made to the numerical determination of the input count rates by an iterative method.
15 Dec 1989
TL;DR: In this article, the authors reported results on hadroproduction of charm based on a sample of {similar to}750 {ital D} mesons. But the results were based on the invariant mass of secondary vertices.
Abstract: We report results on hadroproduction of charm based on a sample of {similar to}750 {ital D} mesons. Charmed particles, produced in a thin segmented target of Si and W by a 340 GeV/c {pi}{sup {minus}} beam and selected by a novel trigger with an enrichment factor of {similar to}15, are identified by the invariant mass of secondary vertices. Data were collected with the {Omega}{prime} spectrometer at the CERN SPS supplemented by a silicon microstrip vertex detector. Assuming the parameterization {sigma}({pi}{sup {minus}}{ital N}{r arrow}{ital DX}){similar to}{ital A{alpha}} where {ital A} is the atomic number, we find {alpha}=0.89{plus minus}0.05{plus minus}0.05 for a data sample with an average x{sub F} of 0.2. The x{sub F} and {ital p}{sub {perpendicular}} distributions of the charged {ital D} mesons are also described and the possibility of a leading effect is investigated.
TL;DR: In this paper, the absorption spectra of polythiophene and polyacetylene solitons were calculated using the VEH method and the results were shown to be in good agreement with experimental observations.
TL;DR: In this article, the chemical composition of films and substrates during sputter deposition is studied by electron-induced X-ray emission, where the sputtering chamber is coupled with a vacuum Xray spectrometer allowing the analysis of Xray emission induced by the high energy (up to 4 keV) electrons of sputtering discharge (rf or d.c. mode).
TL;DR: The main fragmentation pathway of ionized hydroxyallenes (1) consists of a methyl loss as discussed by the authors, also giving rise, by methyl loss, to acylium ions a.k.a. propenyl-acylium structure.
Abstract: The main fragmentation pathway of ionized hydroxyallenes (1) consists of a methyl loss. Extensive deuterium-labelling experiments indicate that the terminal allenic carbon is implied in this fragmentation. Collisional activation spectra indicate a propenyl-acylium structure (a) for these [M – CH3]+ ions which can originate from a 1,4-hydroxyl migration followed by hydrogen rearrangements. Isomeric hydroxyacetylenes (2) behave similarly, also giving rise, by methyl loss, to acylium ions a. It is proposed that 2+ ˙ is irreversibly isomerized into 1+ ˙ by a 1,3-hydrogen transfer ‘catalysed’ by the hydroxy group. The proposed internal proton-bound complex justifies also the easier loss of water from 2+˙. Ethyl loss is also a prominent fragmentation for the hydroxyallene and hydroxy-acetylene homologues.
01 Jan 1989
TL;DR: In this paper, the steady state properties of the bimolecular surface reaction were investigated using the mean field approximation (MFA) type and the resulting kinetic phase transition points, bistability and hysteresis characteristics were compared with those obtained by Monte Carlo simulations performed on a sequential computer or on a parallel one.
Abstract: In order to investigate the steady state properties of the bimolecular surface reaction
$$A + \frac{1} {2}B_2 \to AB $$
on catalytic surfaces, we derive kinetic equations of the mean field approximation (MFA) type and we compare resulting kinetic phase transition points, bistability and hysteresis characteristics with those obtained by Monte Carlo simulations performed on a sequential computer or on a parallel one (which requires the construction of a probabilistic CA machine).