Showing papers by "University of Mons published in 2001"

On T2-shortening by weakly magnetized particles: the chemical exchange model.

Abstract: Chemical exchange (CE) theory is compared with two theories of T2-shortening caused by microscopic magnetic centers: inner- and outer-sphere relaxation theory (long-echo limit) and mean gradient diffusion theory (short-echo limit). The CE equation is shown to be identical to these theories in the respective limits and appropriate parameter relationships are derived for spherical particles. The theories are then compared with computer simulations of spherical particles and with a recent general theory, with good agreement in the asymptotic regions. The CE model also reproduces the essential relaxation characteristics in the intermediate range. Finally, good agreement of a CE model with simulations for magnetized cylinders is also demonstrated. The discussion is limited to weakly magnetized particles such that the maximum phase shift during an echo interval is less than one radian, permitting the use of the Luz-Meiboom CE equation. Published 2001 Wiley-Liss, Inc.

Scaling laws in the macro-, micro- and nanoworlds

Abstract: The microworld and the nanoworld are now of interest to the public, scientists, engineers and industrialists. Effects negligible at the macroscopic level become important at the micrometre scale, and vice versa. Moreover, at the nanoscale, quantum effects may become dominant. Scaling laws are useful for an understanding of the origin of such differences and/or to generalize results obtained at various scales. It is the aim of this paper to examine scaling laws relevant to mechanics, fluids, electromagnetism, thermodynamics, optics and quantum mechanics. Examples related to biology, micromachines and nanotechnologies are treated to show the usefulness of the scaling laws. In recent years, interest in the domains of the microworld and the nanoworld has increased rapidly. The advent of so-called mesoscopic physics, the development of micromachines or micro-electrical mechanical systems (MEMS), the synthesis of nanotubes, the development of nanotechnology, etc… are among the most cited subjects. From both the fundamental and applied points of view, there are interesting questions about these micro- and nanoworlds. In particular, effects negligible at the macroscopic level are important at the micrometre scale, and vice versa. Moreover, when one goes from the macroworld to the nanoworld, one passes through two diffuse limits. When the characteristic dimensions of the elements decrease from the macroscopic to the micrometre size, the effects of gravity become negligible as compared with adhesive and friction effects. Surface tension dominates gravity; other examples are given later. This implies that our reasoning, based on our experience at the macroscopic level, is no longer valid. We have to modify our rules of thinking. The boundary between the macroscopic and microscopic levels is not sharp; it depends on the effect to be considered. When the characteristic size decreases further to attain the nanometre range, another limit is encountered. While the macroscopic properties of matter remain generally valid at the micrometre size, surface effects become dominant at the nanometre scale. Moreover, when one reaches the interatomic distance range, quantum effects appear. 0143-0807/01/060601+11$30.00 © 2001 IOP Publishing Ltd Printed in the UK 601

Dynamics of wetting

Abstract: We review the mechanisms controlling the dynamics of wetting in partial and complete wetting regimes. It is shown that the behaviour in several timescales may characterize the dynamics since different channels of energy dissipation have to be considered within spreading.

Corporate governance in microfinance organizations: along and winding road

Abstract: Over the last few years, more and more attention has been devoted to microfinance by academics and practitioners interested in development issues. This paper is part of this trend, as it tries to identify to what extent the corporate governance framework can be applied to microfinance organizations. Therefore, after considering some of the key issues, it tries to show how relevant these issues are to the microfinance industry.

Proteomics as the tool to search for lung disease markers in bronchoalveolar lavage

Abstract: Most lung disorders are known to be associated to considerable modifications of surfactant composition Numerous of these abnormalities have been exploited in the past to diagnose lung diseases, allowing proper treatment and follow-up Diagnosis was then based on phospholipid content, surface tension and cytological features of the epithelial lining fluid (ELF), sampled by bronchoalveolar lavage (BAL) during fiberoscopic bronchoscopy Today, it appears that the protein content of ELF displays a remarkably high complexity, not only due to the wide variety of the proteins it contains but also because of the great diversity of their cellular origins The significance of the use of proteome analysis of BAL fluid for the search for new lung disease marker proteins and for their simultaneous display and analysis in patients suffering from lung disorders has been examined

Cultivation of Paracentrotus lividus (Echinodermata: Echinoidea) on extruded feeds: digestive efficiency, somatic and gonadal growth.

Abstract: This study assessed the use of extruded feeds, in the form of pellets, for the growing of echinoid Paracentrotus lividus within a closed-culture system. Two feed types, one with soya-bean protein, the other with both soya-bean and fish protein were compared with dried Lessonia sp. and fresh Laminaria sp. as food sources. Pellets present a very high conversion efficiency (about 80%) against about 50% for Laminaria and 35% for Lessonia. However, as pellets are less absorbed, somatic growth (SG) is statistically equivalent for the sea urchins fed with pellets and Laminaria between 2 and 2.2% g soma day–1. Sea urchins fed with pellets produced significantly more gonadal tissue in a shorter time, resulting in a gonadal index (GI) twice higher (6.5%) than Laminaria (3%) in the second month of the experiment. Dry Lessonia does not promote gonadal growth (GG). This study shows that extruded feeds are well assimilated by P. lividus and promote both SG and production of gonadal tissue.

Time-Resolved Laser Spectroscopy of Multiply Ionized Atoms: Natural Radiative Lifetimes in Ce IV

Abstract: Radiative lifetimes have been measured for two excited levels of Ce IV using the time-resolved laser-induced fluorescence technique. Ce3+ ions were produced in a laser-induced plasma. In the measurements, a suitable magnetic field was applied to reduce the recombination between electrons and the ions and thus the background light from the recombination, and special care was exercised to avoid flight-out-of-view effects on the lifetime measurements for the high-velocity ions. The experimental lifetime results, tau = 30(2) ns for the level 49 737 cm(-1) and tau = 30(3) ns for the level 52 226 cm(-1), were compared with relativistic Hartree-Fock calculations (tau = 30.5 and 30.0 ns) indicating a particularly excellent agreement.

Semirelativistic Lagrange mesh calculations.

Abstract: The Lagrange mesh method is a very powerful procedure to compute eigenvalues and eigenfunctions of nonrelativistic Hamiltonians. The trial eigenstates are developed in a basis of well-chosen functions and the computation of Hamiltonian matrix elements requires only the evaluation of the potential at grid points. It is shown that this method can be used to solve semirelativistic two-body eigenvalue equations. As in the nonrelativistic case, it is very accurate, fast, and very simple to implement.

A history of mammalian embryological research.

Abstract: Although Reinier DE GRAAF (1641-1673) can be considered the founder of modern reproductive biology, scientific knowledge of mammalian development did not progress significantly until the XlXth century. Determining contributions to this progress were the discovery of the ovum by Karl von BAER (1792-1876), his meticulous observations of the stages of embryogenesis, and, half a century later, the remarkable descriptions made by Edouard VAN BENEDEN (1845-1910) of egg development in rabbits and bats. Yet mammalian embryology remained a purely descriptive discipline until the second half of the XXth century, when a handful of exceptional scientists (notably including John D. BIGGERS, Ralph BRINSTER, Anne McLAREN, and W. WHITTEN) managed to obtain reproducibly the development of mouse eggs in a chemically defined medium and to transfer the eggs to the uterine horns of pseudopregnant females. Around the same time (1959), M.C. CHANG was the first to obtain a mammal (a rabbit) by in vitro fertilisation, thus opening the way to assisted procreation. This was achieved in our species in 1978, by Robert EDWARDS and Patrick STEPTOE. With these feats, mammalian embryology could at last become causal, as A. BRACHET already in 1912 had hoped it would. New concepts soon emerged from the delicate manipulations performed on mouse eggs by scientists such as A. TARKOWSKI, B. MINTZ, J. MULNARD, and R. GARDNER, concepts such as the oustside-inside hypothesis proposed to explain the determination of the ICM and trophectoderm or the clonal theory of cell determination during development. These new ideas were soon to become the focus of intense study. Other investigators, interested in the synthesis and roles of macromolecules, contributed in the late 1960's most of our knowledge on global trends in gene expression during the first stages of development. As for the many unfruitful attempts to obtain artificial parthenogenetic development in mice, these would lead to the discovery of parental genetic imprinting. In the 1950's, Leroy STEVENS and Barry PIERCE made famous a very rare tumour, the teratocarcinoma. This tumour soon became a model for studying mammalian development, adopted by an increasing number of research groups. It became the source of a first generation of pluripotent cells culturable in vitro: embryonal carcinoma (EC) cells. In the 1980's came the next generation: embryonic stem (ES) cells derived from the ICM of blastocysts, whose advent coincided with that of the first transgenic mice. Then came the era of knockout mice and cloning. Scientists now envisage with enthusiasm applications that were unimaginable just a few years ago. Such is the legacy of those few pioneers of the experimental embryology of mammals who, in the late fifties, were striving to make the wish expressed by A. Brachet in 1912 come true at last.

Core-polarization effects and radiative lifetime measurements in Pr III

Abstract: New radiative lifetimes of eight levels in Pr III have been measured using the time-resolved laser-induced fluorescence method. A tunable frequency-doubled dye laser with 1-ns pulse duration was used to excite selectively doubly ionized praseodymium in a laser-produced plasma. The experimental results agree generally well with theoretical data, provided core-polarization effects are considered in the calculations in an adequate way.

Nuclear magnetic relaxation dispersion of ferritin and ferritin-like magnetic particle solutions: a pH-effect study.

Abstract: The relaxation mechanism of water protons in the presence of ferritin is still being debated. In this work, the pH dependence of the relaxation induced by ferritin and FercaylT, a ferritin-like akaganeite particle, is studied through T1 and T2 nuclear magnetic relaxation dispersion (NMRD) profiles. To differing extents, the relaxation brought about by both systems is significantly affected by pH. A proton exchange time of 33 ns (at pH 6 and 37°C) is deduced from the fittings of FercaylT T1 NMRD profiles. The linearity of the relationship between 1/T2 and the magnetic field B0 for ferritin and FercaylT solutions is not altered by changes in pH. The parameters of this linearity strongly depend on pH for the latter, while remaining unchanged for the former. These results are interpreted in terms of an exchange between protons belonging to hydroxyl groups at the surface of the particle and bulk water protons. Magn Reson Med 46: 476 ‐ 481, 2001. © 2001 Wiley-Liss, Inc.

Uniqueness of the asymptotic AdS3 geometry

Abstract: We show explicitly that in (2 + 1) dimensions the general solution of the Einstein equations with negative cosmological constant on a neighbourhood of timelike spatial infinity can be obtained from BTZ metrics by coordinate transformations corresponding geometrically to deformations of their spatial infinity surface. Thus, whatever the topology and geometry of the bulk, the metric on the timelike extremities is BTZ.

Extended Analysis of the Spectrum of Triply-ionized Ytterbium (Yb IV) and Transition Probabilities

Abstract: The spectrum of Yb IV has been reinvestigated and its analysis has been extended. The present work is supported by the comparison of line intensities with transition probabilities derived from the Cowan (1981) codes. Starting from the first analysis by Sugar, Kaufman and Spector (1978), the number of established levels has been increased from 111 to 193, including high excitation levels of the new 4f127s + 4f126d even configurations. Of the 1023 classified lines about one half are new. Computed transition probabilities are given for selected lines.

Radiative lifetime measurements and transition probabilities of astrophysical interest in Er iii

Abstract: Radiative lifetimes of seven excited states of Er iii have been measured using time-resolved laser-induced fluorescence following two-photon excitation. Relativistic Hartree-Fock calculations taking core-polarization effects into account are found to be in excellent agreement with the experimental results. A large set of new calculated transition probabilities is presented for many transitions of astrophysical interest. These results will be useful for investigating the composition of chemically peculiar stars.

Experimental and Theoretical Energy Levels, Transition probabilities and Radiative Lifetimes in Yb III

Abstract: The analysis of the spectrum of Yb III has been extended allowing us to establish 11 new energy level values. In addition, radiative lifetimes of two excited states of Yb III have been measured for the first time using time-resolved laser-induced fluorescence following two-photon excitation. The good agreement between experimental results and semi-empirical calculations performed with the relativistic Hartree-Fock method including core-polarization effects allows the determination of transition probabilities for 15 lines.

Experimental and theoretical lifetimes in Yb III

Abstract: Lifetimes of three levels belonging to the configuration 4f135d with J = 1 in Yb III have been measured for the first time using the time-resolved laser-induced fluorescence method. Experimental transition probabilities have been deduced for the transitions between the levels studied and the ground state. The comparison of the experimental lifetimes with theoretical data, deduced within the relativistic Hartree-Fock (HFR) approach, underlines the dramatic importance of an adequate consideration of core-polarization effects in the theoretical model and the sensitivity of one of the lifetime values to small correlation effects.

Poly(?-caprolactone-b-glycolide) and poly(D,L-lactide-b-glycolide) diblock copolyesters: Controlled synthesis, characterization, and colloidal dispersions

Abstract: Living ω-aluminum alkoxide poly-ϵ-caprolactone and poly-D,L-lactide chains were synthesized by the ring-opening polymerization of ϵ-caprolactone (ϵ-CL) and D,L-lactide (D,L-LA), respectively, and were used as macroinitiators for glycolide (GA) polymerization in tetrahydrofuran at 40 °C. The P(CL-b-GA) and P(LA-b-GA) diblock copolymers that formed were fractionated by the use of a selective solvent for each block and were characterized by 1H NMR spectroscopy and differential scanning calorimetry analysis. The livingness of the operative coordination–insertion mechanism is responsible for the control of the copolyester composition, the length of the blocks, and, ultimately, the thermal behavior. Because of the inherent insolubility of the polyglycolide blocks, microphase separation occurs during the course of the sequential polymerization, resulting in a stable, colloidal, nonaqueous copolymer dispersion, as confirmed by photon correlation spectroscopy. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 294–306, 2001

Force-velocity relation and density profiles for biased diffusion in an adsorbed monolayer

Abstract: We study the dynamics of a hard-core tracer particle (TP), performing a biased random walk in an adsorbed monolayer composed of mobile hard-core particles undergoing continuous exchanges with a vapor phase. In terms of an approximate approach, based on the decoupling of the third-order correlation functions, we obtain the density profiles of the monolayer particles around the TP, and derive the force-velocity relation, determining the TP terminal velocity ${V}_{\mathrm{tr}}$ as a function of the magnitude of the external bias and other system parameters. These results generalize, for the case of an arbitrary applied field, our earlier predictions [Phys. Rev. Lett. 84, 511 (2000)] obtained in the limit of a vanishingly small external bias. Asymptotic forms of the monolayer particle density profiles at large separations from the TP, and the behavior of ${V}_{\mathrm{tr}}$ in the limit of a small external bias, are found explicitly.

Classical solutions in the Einstein-Born-Infeld-Abelian-Higgs model

Abstract: We consider the classical equations of the Born-Infeld-Abelian-Higgs model (with and without coupling to gravity) in an axially symmetric ansatz. A numerical analysis of the equations reveals that the (gravitating) Nielsen-Olesen vortices are smoothly deformed by the Born-Infeld interaction, characterized by a coupling constant ${\ensuremath{\beta}}^{2},$ and that these solutions cease to exist at a critical value of ${\ensuremath{\beta}}^{2}.$ When the critical value is approached, the length of the magnetic field on the symmetry axis becomes infinite.

Experimental determination of the viscosity at the nanometer scale on a block copolymer with an oscillating nanotip

Abstract: This work is an attempt to investigate viscosities at the nanometer scale To do so, the tapping mode atomic force microscopy is used on a triblock copolymer exhibiting a well-defined periodic structure at the nanometer scale Variations of the oscillator amplitude and phase delay as a function of the tip-sample distance are recorded on the glassy and rubbery domains of the copolymer The experimental data are compared to analytical expressions derived from Stokes law In the present study, among the different possible expressions of the viscous forces depending on the tip shape and on the experimental length scale, only a force proportional to the indentation depth is able to describe the experimental data In this particular case, quantitative measurements are possible Finally, the oscillator is shown to be sensitive to local variations of the viscosity within few nanometers