Showing papers by "University of Mons published in 2002"
TL;DR: A “partial refocusing model” is introduced, based on a spatial division between an inner region where the gradients are too strong for the refocusing pulses to be efficient and an outer region where they are efficient, which agrees with published simulations of relaxation induced by magnetic dipoles approximated as points.
Abstract: Computer simulations of water transverse relaxation induced by superparamagnetic particles are shown to disagree with the available theories, covering the slow diffusion domain. Understanding these new simulations, not in the slow diffusion domain, thus requires a new theoretical approach. A "partial refocusing model" is introduced for this purpose; it is based on a spatial division between an inner region where the gradients are too strong for the refocusing pulses to be efficient and an outer region where they are efficient. This model agrees with published simulations of relaxation induced by magnetic dipoles approximated as points. The validity domains of the various models are also compared.
257 citations
TL;DR: This work considers that the contact angle between the liquid meniscus and the inner surface of the capillary becomes a dynamic contact angle when the liquid front is in movement and suggests an analytical approach of the classical Lucas-Washburn equation (LWE).
238 citations
TL;DR: In this article, the optical properties of poly(fluorene)s containing ketonic defects were analyzed using quantum-chemical techniques, focusing on the influence of excited-state localization effects.
Abstract: Poly(fluorene)-type materials are widely used in polymer-based light emitting devices. In their pristine state, they emit in the deep blue spectral region. During operation there appears, however, an additional emission peak at around 2.3 eV. This observation has usually been attributed to aggregate or excimer formation. Recently, it has been shown that photo- and/or electro-oxidation of poly(fluorene) chains resulting in ketonic defects (i.e., formation of fluorenone groups) can also be held responsible for emission in that spectral region. In this contribution, we apply quantum-chemical techniques to gain a detailed understanding of the optical properties of poly(fluorene)s containing ketonic defects. In particular, we compare model systems for poly(fluorene) with their ketone-containing counterparts, focusing on the influence of excited-state localization effects. The results of the theoretical calculations are confirmed by experimental investigations on statistical copolymers of fluorene and 9-fluorenone.
187 citations
TL;DR: A specific multicriteria socio-technical approach to facilitating bid evaluation processes is presented and several issues that warrant its use are discussed, including practical aspects of structuring criteria and creating a computer-based additive value model in direct interaction with Evaluation Committees responsible for bid evaluation.
Abstract: A speci2c multicriteria socio-technical approach to facilitating bid evaluation processes is presented and several issues that warrant its use are discussed. Some real-world interventions in international public call for tenders illustrate practical aspects of structuring criteria and creating a computer-based additive value model in direct interaction with Evaluation Committees responsible for bid evaluation, supported by the MACBETH approach. ? 2002 Elsevier Science Ltd. All rights reserved.
162 citations
TL;DR: The charge transfer is shown to proceed in these compounds through two competing mechanisms, coherent (superexchange) versus incoherent (bridge-mediated) pathways.
Abstract: Quantum-chemical techniques are applied to model the mechanisms of photoinduced charge transfer from a π-electron donating group (tetracene, D) to a π-electron-acceptor moiety (pyromellitimide, A) separated by a bridge of increasing size (p-phenylenevinylene oligomers, B). Correlated Hartree−Fock semiempirical approaches are exploited to calculate the four main parameters controlling the transfer rate (kRP) in the framework of Marcus−Jortner−Levich's formalism: (i) the electronic coupling between the initial and final states; (ii) and (iii) the internal and external reorganization energy terms; and (iv) the variation of the free Gibbs energy. The charge transfer is shown to proceed in these compounds through two competing mechanisms, coherent (superexchange) versus incoherent (bridge-mediated) pathways. While superexchange is the dominant mechanism for short bridges, incoherent transfer through hopping along the phenylene vinylene segment takes over in longer chains (for ca. three phenylenevinylene repea...
120 citations
TL;DR: In this article, the authors studied infrared absorptions in working polymer light-emitting diodes due to the presence of polarons and triplet excitons and found that the polaron population is proportional to the applied voltage, providing direct evidence for space-charge-limited currents.
93 citations
TL;DR: Comparison with other chemiluminescence methods indicates that the described method is the only one to detect the stimulation of starfish immunocytes by the Gram-positive bacteria, Micrococcus luteus, a fact that questions previous reports indicating a lack of stimulation by pathogens.
86 citations
TL;DR: In this paper, the emission properties of polyindenofluorenes with various proportions of straight-and branched-chain alkyl substituents have been compared.
Abstract: The emission properties of polyindenofluorenes with various proportions of straight- and branched-chain alkyl substituents have been compared. The polymer with straight octyl substituents shows green emission due to formation of aggregates, while the polymer with branched 2-ethylhexyl substituents shows blue emission. Studies of the film morphology show the presence of ordered structures due to π-stacking of the polymer chains for the octyl-substituted polymer, whereas the polymer with branched side-chains shows no such order. Copolymers show intermediate behavior. A clear correlation is established between the degree of straight-chain alkyl substitution, the formation of ordered structures in the films, and the amount of long wavelength emission in the solid-state spectra.
75 citations
TL;DR: In this paper, the geometric and electronic structures of poly(3,4-ethylenedioxythiophene)-PEDOT have been studied and the relative stability of two possible structures for PEDOT (aromatic-like and quinoid-like) has been evaluated on oligomers of increasing size.
67 citations
TL;DR: In this paper, a systematic investigation of spectroscopic properties of lanthanide ions (Z=57-71) was carried out using time-resolved laser-induced fluorescence following one- or two-photon excitations.
66 citations
Journal Article•
TL;DR: Some generalizations of k-automatic sequences replacing the k-ary system by an abstract numeration system on a regular language are given and the equivalence of these sequences and morphic predicates is given.
Abstract: We give some generalizations of k-automatic sequences replacing the k-ary system by an abstract numeration system on a regular language. We study some of the closure properties of these sequences and the possible extension to the multidimensional case or to infinite alphabets. The equivalence of these sequences and morphic predicates is given and the relationship to recognizability is also investigated.
TL;DR: In this article, the authors constructed globally regular and non-abelian solutions of a higher order curvature EYM model in $d=5$ dimensions, which consists of the superposition of the first two members of the gravitational hierarchy (Einstein plus first Gauss-Bonnet(GB)) interacting with the second and third Yang-Mills hierarchy.
Abstract: We construct globally regular as well as non-abelian black hole solutions of a higher order curvature Einstein-Yang-Mills (EYM) model in $d=5$ dimensions. This model consists of the superposition of the first two members of the gravitational hierarchy (Einstein plus first Gauss-Bonnet(GB)) interacting with the superposition of the first two members of the $SO(d)$ Yang--Mills hierarchy.
TL;DR: In this paper, the authors presented an alternative identification for the line detected in the spectra of s-process enriched low-mass post-AGB stars around 6708 A and which was interpreted in the literature as due to Li.
Abstract: In this letter we present an alternative identification for the line detected in the spectra of s-process enriched low-mass post-AGB stars around 6708 A and which was interpreted in the literature as due to Li. Newly released line lists of lanthanide species reveal, however, the likely identification of the line to be due to a Ceii transition. We argue that this identification is consistent with the Ce abundance of all the objects discussed in the literature and conclude that in none of the low-mass s-process enriched post-AGB stars there is indication for Li-production.
TL;DR: In this paper, the emergence of a minimal length for a large class of generalized commutation relations, preserving position operators and translation invariance as well as rotation invariance, was analyzed.
Abstract: We analyze the emergence of a minimal length for a large class of generalized commutation relations, preserving commutation of the position operators and translation invariance as well as rotation invariance (in dimensions higher than one). We show that the construction of the maximally localized states based on squeezed states generally fails. Rather, one must resort to a constrained variational principle.
TL;DR: The present paper addresses the question of amoebocyte differentiation in the starfish Asterias rubens when challenged by bacteria and suggests that the high efficiency of the immune system in starfishes is related to this fast reaction.
TL;DR: A simple model of spacetime foam made by N wormholes in a semiclassical approximation is taken under examination and the Casimir-like energy of the quantum fluctuation of such a model and its probability of being realized are computed.
Abstract: A simple model of spacetime foam, made by N wormholes in a semiclassical approximation, is taken under examination. The Casimir-like energy of the quantum fluctuation of such a model and its probability of being realized are computed. Implications on the Bekenstein–Hawking entropy and the cosmological constant are considered.
19 Aug 2002
TL;DR: In this paper, the numerical index of a Banach space from the isomorphic point of view was studied and it was shown that for most Banach spaces the least upper bound of this interval is as large as possible, namely 1.
Abstract: We study the numerical index of a Banach space from the isomorphic point of view, that is, we investigate the values of the numerical index which can be obtained by renorming the space. The set of these values is always an interval which contains [0,1/3[ in the real case and [e -1 ,1/2[ in the complex case. Moreover, for most Banach spaces the least upper bound of this interval is as large as possible, namely 1.
TL;DR: In this paper, the dynamics of spontaneously spreading drops of viscous liquids on top of porous medium made by non-interconnected pores is studied and a model for the single pore case is proposed on a theoretical basis and validated by molecular dynamics simulations.
Abstract: We study the dynamics of spontaneously spreading drops of viscous liquids on top of porous medium made by non-interconnected pores. A model for the single pore case is proposed on a theoretical basis and validated by molecular dynamics simulations. The generalization to the multiple non-interconnected pore cases allows unique characterization of the dynamics of spreading on a porous surface by essentially two parameters referring to the size of the considered pores and the friction between the liquid and the considered surfaces.
TL;DR: In this article, the formation rates for singlet and triplet excitons associated with intermolecular charge transfer processes are calculated and it is found that the interchain bond-charge correlation has a strong influence on the singlet/triplet ratio.
Abstract: The coupled-cluster equation of motion approach is applied to describe positively and negatively charged states as well as exciton states in conjugated polymers. The formation rates for singlet and triplet excitons associated with intermolecular charge-transfer processes are calculated. It is found that the interchain bond-charge correlation has a strong influence on the singlet/triplet ratio, since the charge-transfer configuration contributes differently to the singlet and triplet excitons. In addition, we find that the range of electron interaction potential has a strong influence on the formation rates. The ratio between the electroluminescence and photoluminescence quantum yields can exceed the 25% spin-degeneracy statistical limit.
TL;DR: The physical interpretation of nuclear rainbow scattering within the frame of the optical model is critically investigated.
Abstract: The physical interpretation of nuclear rainbow scattering within the frame of the optical model is critically investigated. Starting from the properties of the Luneburg lens, a gradient index device that displays refractive features similar to those of the nuclear potential, important differences between the mechanisms producing the nuclear and optical rainbows are pointed out.
TL;DR: In this paper, the H-bonding interaction between the oxopurine base hypoxanthine and water was investigated using matrix-isolation FT-IR spectroscopy combined with theoretical density functional theory and ab initio methods.
Abstract: The H-bonding interaction between the oxopurine base hypoxanthine and water is investigated using matrix-isolation FT-IR spectroscopy combined with theoretical density functional theory and ab initio methods. For vibrational frequency predictions, only the DFT/B3-LYP method is used, while for the prediction of relative energies and H-bond interaction energies of the complexes, four different theoretical methods are compared, i.e., RHF//RHF, MP2//RHF, DFT//DFT, and MP2//DFT. The oxo-N1HN7H, the oxo-N1HN9H, and the hydroxy-N9H (rotamer with the hydroxy-H atom pointed toward the N1 atom) are found to be the three most stable tautomeric forms of the free base. Different, stable complexes between these three tautomers and water have been predicted theoretically. The experimental FT-IR spectra agree well with this prediction, and most of the characteristic spectral data for the four most stable closed complexes, N7H···OH···OC6 and N1H···OH···OC6 of the O17 tautomer and N1H···OH···OC6 and N9H···OH···N3 of the O1...
Journal Article•
TL;DR: The investigation of influence of molecular structure of macrocyclic pyridinophanes, their analogues and certain other compounds on anticancer and antiviral activity has been carried out by means of the 4D-QSAR.
Abstract: A new 4D-QSAR approach has been considered. For all investigated molecules the 3D structural models have been created and the set of conformers (fourth dimension) have been used. Each conformer is represented as a system of different simplexes (tetratomic fragments of fixed structure, chirality and symmetry). The investigation of influence of molecular structure of macrocyclic pyridinophanes, their analogues and certain other compounds on anticancer and antiviral (anti-influenza, antiherpes and antiadenovirus) activity has been carried out by means of the 4D-QSAR. Statistic characteristics for QSAR of PLS (partial least squares) models are satisfactory (R = 0.92-0.97; CVR = 0.63-0.83). Molecular fragments increasing and decreasing biological activity were defined. This information may be useful for design, and direct synthesis of novel anticancer and antiviral agents.
TL;DR: In this article, the mechanisms of the internal nucleophilic substitution reactions leading to these products have been detailed at the MP2/6-31G∗ level of theory and the thermochemistry associated with the initial protonation process of 1-4 has been examined up to the G2(MP2,SVP) level.
TL;DR: In this paper, lifetime measurements by time-resolved laser-induced fluorescence spectroscopy for 5 levels belonging to the 4f(3)5d configuration of doubly ionized neodymium provide a first and useful experimental test of the relativistic Hartree-Fock calculations in this ion of astrophysical interest.
Abstract: Selective lifetime measurements by time-resolved laser-induced fluorescence spectroscopy for 5 levels belonging to the 4f(3)5d configuration of doubly ionized neodymium provide a first and useful experimental test of the relativistic Hartree-Fock calculations in this ion of astrophysical interest. As a consequence, the accuracy of the transition probabilities deduced in the present work is well assessed. These new data are expected to help astrophysicists in the future to refine the analysis of the composition of chemically peculiar stars which frequently show large overabundances of lanthanides when compared to the solar system standards.
TL;DR: In this article, the effect of the current (20-65 mA) and the argon pressure (5-20 mtorr) on the films morphology was analyzed by electron spectroscopy for chemical analysis (ESCA) and atomic force microscopy (AFM).
Abstract: Silver thin films (1–10 nm thick) were deposited on titanium by magnetron sputtering. We study the effect of the current (20–65 mA) and the argon pressure (5–20 mtorr) on the films morphology. Their structure is characterized by electron spectroscopy for chemical analysis (ESCA) and atomic force microscopy (AFM). The ESCA data are analysed by means of the quases ™ code. The data are fitted by means of a model in which the surface is assumed to be composed of two kinds of features: islands and a thin layer. It is shown that the islands coverage coefficient may attain 95%. The films are also characterized by AFM. It appears that the surface roughness is important, due to the roughness of the initial Ti film. A comparison of the AFM and quases ™ results shows that the structure is such that clusters of Ti are covered by a thin layer of Ag. The space between Ti clusters is filled with clusters of Ag. The coverage and the thickness of the films depend on the deposition rate and the total argon pressure.
TL;DR: In this article, the authors revisited the non-rotating massive BTZ black hole within a pseudo-Riemannian symmetric space context, and they found that every such space intrinsically carries a regular Poisson structure whose symplectic leaves are para-Hermitian symmetry surfaces.
TL;DR: In this article, the spectra of mesons and baryons, composed of light quarks, were studied in the framework of a semirelativistic potential model including instanten induced forces.
Abstract: We study the spectra of mesons and baryons, composed of light quarks, in the framework of a semirelativistic potential model including instanten induced forces. We show how a simple modification of the instanton interaction in the baryon sector allows a good description of the meson and the baryon spectra using an interaction characterized by a unique set of parameters.
TL;DR: In this paper, the importance of core-polarization effects on oscillator strength determination in Ce iii is emphasized, and the inclusion of these effects in relativistic Hartree-Fock (HFR) calculations leads to theoretical lifetime values for some 4f6p levels of this ion in close agreement with recent time-resolved laser-induced fluorescence measurements.
Abstract: The importance of core-polarization effects on oscillator strength determination in Ce iii is emphasized. The inclusion of these effects in relativistic Hartree–Fock (HFR) calculations leads to theoretical lifetime values for some 4f6p levels of this ion in close agreement with recent time-resolved laser-induced fluorescence measurements. These new atomic data, the most accurate to date, have allowed the refinement of the stellar abundance determination of cerium in the chemically peculiar star HD 192913, but have not altered in a drastic way the conclusions derived in recent analyses regarding the overabundance of this element.
TL;DR: In this paper, the hollow-cathode spectra of neutral vanadium were recorded by Fourier transform spectroscopy in the near infrared -visible region (9000-17 000 cm-1).
Abstract: We have recorded hollow-cathode spectra of neutral vanadium by Fourier transform spectroscopy in the near infrared – visible region (9000–17 000 cm-1). 36 transitions showing hyperfine structure have been analyzed, allowing us to deduce magnetic dipole constants for 27 levels belonging to the 3d44p and 3d34s4p configurations. For 22 of these levels no data were previously available.
TL;DR: In this article, the first lifetime measurements have been performed for six levels of doubly ionized thorium, an important cosmochronometer in astrophysics for estimating the age of the Galaxy.
Abstract: The first lifetime measurements have been performed for six levels of doubly ionized thorium, an important cosmochronometer in astrophysics for estimating the age of the Galaxy. The levels, belonging to the 5f2, 5f7p, 7s7p, and 6d7p configurations of Th III, have been measured by the time-resolved laser-induced fluorescence method and compared with relativistic Hartree-Fock calculations including configuration interaction and core-polarization effects. Taking advantage of the excellent agreement between theory and experiment, a first set of transition probabilities of astrophysical interest has been deduced for this ion from a combination of the experimental lifetimes and of the theoretical branching fractions.