Showing papers by "University of Mons published in 2006"

A Taxonomy of Model Transformation

Abstract: This article proposes a taxonomy of model transformation, based on the discussions of a working group on model transformation of the Dagstuhl seminar on Language Engineering for Model-Driven Software Development. This taxonomy can be used, among others, to help developers in deciding which model transformation language or tool is best suited to carry out a particular model transformation activity.

Search for neutral MSSM Higgs bosons at LEP

Abstract: The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses of neutral Higgs bosons.

Minimal length uncertainty relation and gravitational quantum well

Abstract: The dynamics of a particle in a gravitational quantum well is studied in the context of nonrelativistic quantum mechanics with a particular deformation of a two-dimensional Heisenberg algebra. This deformation yields a new short-distance structure characterized by a finite minimal uncertainty in position measurements, a feature it shares with noncommutative theories. We show that an analytical solution can be found in perturbation and we compare our results to those published recently, where noncommutative geometry at the quantum mechanical level was considered. We find that the perturbations of the gravitational quantum well spectrum in these two approaches have different signatures. We also compare our modified energy spectrum to the results obtained with the GRANIT experiment, where the effects of the Earth's gravitational field on quantum states of ultracold neutrons moving above a mirror are studied. This comparison leads to an upper bound on the minimal length scale induced by the deformed algebra we use. This upper bound is weaker than the one obtained in the context of the hydrogen atom but could still be useful if the deformation parameter of the Heisenberg algebra is not a universal constant but a quantity that depends on the energetic content of the system.

Detecting and resolving model inconsistencies using transformation dependency analysis

Abstract: Model inconsistency management is a crucial aspect of model-driven software engineering. It is therefore important to provide automated support for this activity. The problem is, however, that the resolution of inconsistencies may give rise to new inconsistencies. To address this problem, we propose to express inconsistency detection and resolutions as graph transformation rules, and to apply the theory of critical pair analysis to analyse potential dependencies between the detection and resolution of model inconsistencies. As a proof-of-concept, we report on an experiment that we have carried out along these lines using the critical pair analysis algorithm implemented in the state-of-the-art graph transformation tool AGG. The results show that both anticipated and unexpected dependencies between inconsistency detection and resolution rules are found by AGG. We discuss how the integration of the proposed approach into contemporary modelling tools may improve inconsistency management in various ways.

Melt Structure and its Transformation by Sequential Crystallization of the Two Blocks within Poly(L‐lactide)‐block‐Poly(ε‐caprolactone) Double Crystalline Diblock Copolymers

Abstract: Sequential crystallization of poly(L-lactide) (PLLA) followed by poly(epsilon-caprolactone) (PCL) in double crystalline PLLA-b-PCL diblock copolymers is studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS). Three samples with different compositions are studied. The sample with the shortest PLLA block (32 wt.-% PLLA) crystallizes from a homogeneous melt, the other two (with 44 and 60% PLLA) from microphase separated structures. The microphase structure of the melt is changed as PLLA crystallizes at 122 degrees C (a temperature at which the PCL block is molten) forming spherulites regardless of composition, even with 32% PLLA. SAXS indicates that a lamellar structure with a different periodicity than that obtained in the melt forms (for melt segregated samples). Where PCL is the majority block, PCL crystallization at 42 degrees C following PLLA crystallization leads to rearrangement of the lamellar structure, as observed by SAXS, possibly due to local melting at the interphases between domains. POM results showed that PCL crystallizes within previously formed PLLA spherulites. WAXS data indicate that the PLLA unit cell is modified by crystallization of PCL, at least for the two majority PCL samples. The PCL minority sample did not crystallize at 42 degrees C (well below the PCL homopolymer crystallization temperature), pointing to the influence of pre-crystallization of PLLA on PCL crystallization, although it did crystallize at lower temperature. Crystallization kinetics were examined by DSC and WAXS, with good agreement in general. The crystallization rate of PLLA decreased with increase in PCL content in the copolymers. The crystallization rate of PCL decreased with increasing PLLA content. The Avrami exponents were in general depressed for both components in the block copolymers compared to the parent homopolymers. Polarized optical micrographs during isothermal crystalli zation of (a) homo-PLLA, (b) homo-PCL, (c) and (d) block copolymer after 30 min at 122 degrees C and after 15 min at 42 degrees C.

Minimal length uncertainty relation and gravitational quantum well

Abstract: The dynamics of a particle in a gravitational quantum well is studied in the context of nonrelativistic quantum mechanics with a particular deformation of a two-dimensional Heisenberg algebra. This deformation yields a new short-distance structure characterized by a finite minimal uncertainty in position measurements, a feature it shares with noncommutative theories. We show that an analytical solution can be found in perturbation and we compare our results to those published recently, where noncommutative geometry at the quantum mechanical level was considered. We find that the perturbations of the gravitational quantum well spectrum in these two approaches have different signatures. We also compare our modified energy spectrum to the results obtained with the GRANIT experiment, where the effects of the Earth’s gravitational field on quantum states of ultracold neutrons moving above a mirror are studied. This comparison leads to an upper bound on the minimal length scale induced by the deformed algebra we use. This upper bound is weaker than the one obtained in the context of the hydrogen atom but could still be useful if the deformation parameter of the Heisenberg algebra is not a universal constant but a quantity that depends on the energetic content of the system.

Supramolecular assembly of conjugated polymers: From molecular engineering to solid-state properties

Abstract: π-Conjugated polymers are central ingredients in the development of organic electronics and it is well-known that the degree of order in thin films of those materials is a major factor governing the performances of the devices (field effect transistors, light-emitting diodes, photovoltaic cells). In this review, we present some approaches for the control of the molecular assembly of conjugated polymers into well-defined nanostructures. We consider self-assembly leading to thin deposits from compounds molecularly dispersed in a solution and we focus on the relationship between the supramolecular interactions between the individual π-conjugated molecules/polymers and the microscopic morphology appearing upon aggregation. We describe approaches to control the self-assembly of conjugated systems in the solid-state via (i) the interactions with the substrate surface; (ii) the design of a well-defined molecular structure; and (iii) the use of block-copolymers comprising conjugated and non-conjugated blocks. To understand how supramolecular interactions influence the microscopic morphology, we developed a joint experimental–theoretical approach, combining scanning probe microscopy characterization of thin deposits and force-field molecular modeling of supramolecular aggregates and adsorbates. With this methodology, a strong correlation is established between the polymer molecular structure, the degree of supramolecular order, and the solid-state photoluminescence properties (for light-emitting applications), or the charge transport properties (for the design of field-effect transistors). Since the construction of small-size devices requires that the spatial growth of the thin deposits be perfectly controlled, we illustrate in the last section of the paper how soft lithographic methods and nanorubbing can be used to orient the formation of the self-assembled conjugated nanostructures in a confined space.

Applying a Model Transformation Taxonomy to Graph Transformation Technology

Abstract: A taxonomy of model transformations was introduced in [T. Mens, P.V. Gorp, A taxonomy of model transformation, in: Proc. Int'l Workshop on Graph and Model Transformation (GraMoT 2005), Electronic Notes in Computer Science (2005)]. Among others, such a taxonomy can help developers in deciding which language, forma lism, tool or mechanism is best suited to carry out a particular model transformation activity. In this paper we apply the taxonomy to the technique of graph transformation, and we exemplify it by referring to four representative graph transformation tools. As a byproduct of our analysis, we discuss how well each of the considered tools carry out the activity of model transformation.

The unitary representations of the Poincare group in any spacetime dimension

Abstract: An extensive group-theoretical treatment of linear relativistic field equations on Minkowski spacetime of arbitrary dimension D>2 is presented in these lecture notes. To start with, the one-to-one correspondence between linear relativistic field equations and unitary representations of the isometry group is reviewed. In turn, the method of induced representations reduces the problem of classifying the representations of the Poincare group ISO(D-1,1) to the classication of the representations of the stability subgroups only. Therefore, an exhaustive treatment of the two most important classes of unitary irreducible representations, corresponding to massive and massless particles (the latter class decomposing in turn into the ``helicity'' and the "infinite-spin" representations) may be performed via the well-known representation theory of the orthogonal groups O(n) (with D-4

Spin three gauge theory revisited

Abstract: We study the problem of consistent interactions for spin-3 gauge fields in flat spacetime of arbitrary dimension 3$>n>3. Under the sole assumptions of Poincar? and parity invariance, local and perturbative deformation of the free theory, we determine all nontrivial consistent deformations of the abelian gauge algebra and classify the corresponding deformations of the quadratic action, at first order in the deformation parameter. We prove that all such vertices are cubic, contain a total of either three or five derivatives and are uniquely characterized by a rank-three constant tensor (an internal algebra structure constant). The covariant cubic vertex containing three derivatives is the vertex discovered by Berends, Burgers and van Dam, which however leads to inconsistencies at second order in the deformation parameter. In dimensions 4$>n>4 and for a completely antisymmetric structure constant tensor, another covariant cubic vertex exists, which contains five derivatives and passes the consistency test where the previous vertex failed.

Transparent, Plastic, Low-Work-Function Poly(3,4-ethylenedioxythiophene) Electrodes

Abstract: Novel applications for flexible electronics, e.g., displays and solar cells, require fully flexible, transparent, stable, and low-work-function electrodes that can be manufactured via a low-cost pr ...

Measuring software flexibility

Abstract: Flexibility has been recognised as a desirable quality of software since the earliest days of software engineering. Classic and contemporary software design literature suggests that particular implementations are more flexible than others, but stops short of suggesting objective criteria for quantifying such claims. To measure software flexibility in precise terms, we introduce the notion of evolution complexity and demonstrate how it can be used to measure and compare the flexibility of (1) programming paradigms (Object-Oriented against Procedural programs), (2) architectural styles (Shared Data, Pipes and Filters, and Abstract Data Type) and (3) design patterns (Visitor and the Abstract Factory). We also demonstrate how evolution complexity can be used to choose the most flexible design policy. We conclude with experimental results corroborating our claims.

Morphology and tenacity of the tube foot disc of three common European sea urchin species: a comparative study

Abstract: The variation in tenacity of single tube feet from three sea urchin species with contrasted habitats was assessed and correlated with the ultrastructure of their adhesive secretory granules. The tube feet of Arbacia lixula and Sphaerechinus granularis have larger discs and more complex adhesive granules than those of Paracentrotus lividus, but A. lixula attaches to glass with significantly lower tenacity (0.05 – 0.09 MPa) than the other two species (0.10 – 0.20 and 0.11 – 0.29 MPa, respectively). However, the estimated maximal attachment force one tube foot can produce is similar for all three species investigated. No clear relationship between tube foot size, tenacity, adhesive secretory granule ultrastructure and species habitat can therefore be established. For P. lividus the tenacity of single tube foot discs on four different smooth substrata was also compared, which showed that both the total surface energy and the ratio of polar to non-polar forces at the surface influence tube foot attach...

How long does it take to pull an ideal polymer into a small hole

Abstract: We present scaling estimates for characteristic times $\tau_{\rm lin}$ and $\tau_{\rm br}$ of pulling ideal linear and randomly branched polymers of $N$ monomers into a small hole by a force $f$. We show that the absorbtion process develops as sequential straightening of folds of the initial polymer configuration. By estimating the typical size of the fold involved into the motion, we arrive at the following predictions: $\tau_{\rm lin}(N) \sim N^{3/2}/f$ and $\tau_{\rm br}(N) \sim N^{5/4}/f$, and we also confirm them by the molecular dynamics experiment.

Parity-violating vertices for spin-3 gauge fields

Abstract: The problem of constructing consistent parity-violating interactions for spin-3 gauge fields is considered in Minkowski space Under the assumptions of locality, Poincar\'e invariance, and parity noninvariance, we classify all the nontrivial perturbative deformations of the Abelian gauge algebra In space-time dimensions $n=3$ and $n=5$, deformations of the free theory are obtained which make the gauge algebra non-Abelian and give rise to nontrivial cubic vertices in the Lagrangian, at first order in the deformation parameter $g$ At second order in $g$, consistency conditions are obtained which the five-dimensional vertex obeys, but which rule out the $n=3$ candidate Moreover, in the five-dimensional first-order deformation case, the gauge transformations are modified by a new term which involves the second de Wit-Freedman connection in a simple and suggestive way

Size, shape and stress effects on the melting temperature of nano-polyhedral grains on a substrate

Abstract: During the first steps of vacuum deposition of thin films, grains appear randomly on the substrate as isolated islands. To characterize the formation of grains in thin films, the melting temperature of grains is studied theoretically as a function of their size and shape. Assuming a liquid grain that is a portion of a sphere, during the liquid–solid transformation the nano-grains could solidify adopting a sphere, portion of sphere, tetrahedron, or parallelepiped shape. These cases are investigated here. The effect of stress on the melting temperature is also considered.

Adhesive Secretions in Echinoderms: A Review

Abstract: Echinoderms are quite exceptional in the sense that most species belonging to this group use adhesive secretions extensively. Two different adhesive systems may be recognised in these animals: the tube feet, organs involved in attachment to the substratum or food capture, and the Cuvierian tubules, organs involved in defence. These two systems rely on different types of adhesion and therefore differ in the way they operate, in their structure and in the composition of their adhesive. Although tube feet are present in every extant echinoderm species, only those of asteroids and regular echinoids have been studied in detail in terms of adhesion. These organs are involved in temporary adhesion, functioning as duo-gland adhesive systems in which adhesive cells release a proteinaceous secretion, while de-adhesive cells allow detachment. To date, only two adhesive proteins have been characterized in echinoderm tube feet, i.e., Sfp1 in sea stars and Nectin in sea urchins. These two proteins do not appear to be related, but they share similar protein–carbohydrate interaction domains. Cuvierian tubules occur only in some holothuroid species. These single-use organs rely on instantaneous adhesion, their contact with a surface triggering the release of the protein-based adhesive from a single cell type. Some proteins have been identified in the adhesive, but no confirmation of their adhesive function has been provided so far.

Measurement and interpretation of fermion-pair production at LEP energies above the Z resonance

Abstract: This paper presents DELPHI measurements and interpretations of cross-sections, forward-backward asymmetries, and angular distributions, for the e+e- -> ffbar process for centre-of-mass energies above the Z resonance, from sqrt(s) ~ 130 - 207 GeV at the LEP collider. The measurements are consistent with the predictions of the Standard Model and are used to study a variety of models including the S-Matrix ansatz for e+e- -> ffbar scattering and several models which include physics beyond the Standard Model: the exchange of Z' bosons, contact interactions between fermions, the exchange of gravitons in large extra dimensions and the exchange of sneutrino in R-parity violating supersymmetry.

Self-organization and nanoscale electronic properties of azatriphenylene-based architectures: A scanning probe microscopy study

Abstract: It is clearthat the performance of device prototypesbased on an ensem-ble of molecules can be improved by achieving full control ofthe supramolecular self-organization of the active organiccomponents, and by elucidating and optimizing many otherphysicochemical properties, such as their complex electronicstructure, both at the single-molecule and supramolecular lev-el. In this context, scanning probe microscopy (SPM) offersdirect, yet quantitative, mapping of a variety of physicochem-ical properties with submolecular resolution.

Viscoelastic dewetting of constrained polymer thin films

Abstract: Thin films of fluids are playing a leading role in countless natural and industrial processes. Here we study the stability and dewetting dynamics of viscoelastic polymer thin films. The dewetting of polystyrene close to the glass transition reveals unexpected features: asymmetric rims collecting the dewetted liquid and logarithmic growth laws that we explain by considering the nonlinear velocity dependence of fric- tion at the fluid/solid interface and by evoking residual stresses within the film. Sys- tematically varying the time so that films were stored below the glass-transition tem- perature, we studied simultaneously the probability for film rupture and the dewetting dynamics at early stages. Both approaches proved independently the significance of re- sidual stresses arising from the fast solvent evaporation associated with the spin-coat- ing process. V C 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3022-3030, 2006

On Killing tensors and cubic vertices in higher-spin gauge theories

Abstract: The problem of determining all consistent non-Abelian local interactions is reviewed in flat space-time. The antifield-BRST formulation of the free theory is an efficient tool to address this problem. Firstly, it allows to compute all on-shell local Killing tensor fields, which are important because of their deep relationship with higher-spin algebras. Secondly, under the sole assumptions of locality and Poincare invariance, all non-trivial consistent deformations of a sum of spin-three quadratic actions deforming the Abelian gauge algebra were determined. They are compared with lower-spin cases. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.

Transition probabilities and lifetimes in neutral and singly ionized osmium and the Solar osmium abundance

Abstract: Radiative lifetime measurements have been performed, with a time-resolved laser-induced fluorescence technique, for 12 levels of Os I and for 9 levels of Os II. For 9 levels of Os I and 4 levels of Os II, there were no previous experimental data available. From a comparison with new theoretical calculations, taking configuration interactions and core-polarization effects into account, it has been possible to deduce oscillator strengths for 129 transitions of Os I and 137 transitions of Os II of astrophysical interest appearing in the wavelength range 180.0–870.0 nm. These results have allowed us to revise the abundance of osmium in the solar photosphere (log eOs = 1.25 ± 0.11). The newly derived oscillator strengths have been applied as well to derive the osmium abundance in the carbon-rich metal-poor star HD 187861.

From a two-dimensional chemical pattern to a three-dimensional topology through selective inversion of a liquid-liquid bilayer.

Abstract: Soft organic surfaces with more and more complex topologies are required daily to engineer appropriate microstructures for many different applications such as DNA array technology1, biological optics for advanced photonic systems2 and microfluidics3,4. Complementarily to conventional lithographic processes5,6, several pioneering methods have been developed recently, by controlling phase separation of polymer blends7,8, spinodal decomposition of homopolymers9,10 or by using the action of additional external forces driving diverse instabilities11,12. Here we present a method that not only provides original concepts towards the three-dimensional (3D) structuring of liquids, on the basis of the synergistic effects of molecular diffusion and confined nucleation, but also suggests original solutions for the transport, mixing and filtering of small volumes of liquid. Through the intrinsic destabilization of a liquid–liquid bilayer, the 2D pattern of a chemically structured surface with ‘hydrophilic’ and ‘hydrophobic’ domains is transferred to a solid/liquid interface as a 3D topography with either ‘positive’ or ‘negative’ replication. This easy-to-use process has potential applications in various technological realms requiring a specific topography at interfaces such as microfluidics or biosensors.

High-resolution carbon isotope stratigraphy and mammalian faunal change at the Paleocene-Eocene boundary in the Honeycombs area of the southern Bighorn Basin, Wyoming

Abstract: The Paleocene-Eocene boundary is defined chemostratigraphically by the onset of a 100 kyr global carbon isotope excursion (CIE) that is recognized in marine and continental strata in both carbonate and dispersed organic carbon. The CIE is important in continental sections as a proxy for environmental change during the Paleocene-Eocene thermal maximum (PETM), which clearly affected faunal succession in Paleocene-Eocene mammals. At Polecat Bench in the northern Bighorn Basin, Wyoming, the CIE is in the Will-wood Formation, where it spans four mammalian biozones from part of latest Clarkforkian Cf-3, through early Wasatchian Wa-M (Meniscotherium), Wa-0, and part of Wa-1. Here we report a new high-resolution study of the CIE recorded in dispersed organic carbon of the basal Willwood Formation in the Honeycombs area of the southern Bighorn Basin. In the Honeycombs area, 58 isotope sample sites span a vertical section of 71 meters, including the Wa-M locality 'Halfway Hill North' with both Meniscotherium and a Heptodonlike perissodactyl, and the richly fossiliferous Wa-0 wash site 'Castle Gardens' yielding a diverse mammalian fauna. Total organic carbon in the Honeycombs section is in the range of 0.1 to 0.4 percent by weight, and CaCO 3 is notably lacking except in the Castle Gardens interval where it reaches ca. 3 percent. Pre- and post-excursion values of δ 13 C org (PDB) range from -26.2 to -24.1 permil. The Honeycombs CIE is about 42 m thick, and CIE excursion values range from -28.8 to -26.2 permil. The Honeycombs area is important because the Halfway Hill North locality is the first to yield a perissodactyl from the Wa-M Meniscotherium zone, and the Castle Gardens wash site is the first to yield abundant evidence of Wa-0 zone microvertebrates. As at Polecat Bench, the Meniscotherium zone in the Honeycombs area is in the lower part of the CIE, and Castle Gardens and other Wa-0 sites are in the longer middle and upper parts, starting near or after the maximum negative excursion. The CIE at Polecat Bench includes a series of 5 to 6 negative-excursion landmarks that are spaced, on average, about 8.5 m apart. These are tentatively interpreted as 21-kyr orbital precession cycles like those inferred for paleosol color. Negative-excursion landmarks are present in the Honeycombs CIE as well, but these are fewer and part of the Honeycombs section may be condensed or missing. Full understanding of the Paleocene-Eocene biotic transition will require investigation at even finer scales of temporal resolution, and results reported here suggest that finer-scale studies should be possible.

Chemical and constitutional influences in the self-assembly of functional supramolecular hydrogen-bonded nanoscopic fibres.

Abstract: A new series of secondary amides bearing long alkyl chains with p-electron-donor cores has been syn- thesized and characterised,and their self-assembly upon casting at surfaces has been studied. The different supra- molecular assemblies of the materials have been visualized by using atomic force microscopy (AFM) and transmis- sion electron microscopy (TEM). It is possible to obtain well-defined fibres of these aromatic core molecules as a result of the hydrogen bonds between the amide groups. Indeed,by altering the alkyl-chain lengths,constitutions, concentrations and solvent,it is possi- ble to form different rodlike aggregates on graphite. Aggregate sizes with a lower limit of 6-8 nm width have been reached for different amide derivatives, while others show larger aggregates with rodlike morphologies which are several micrometers in length. For one compound that forms nanofibres, doping was performed by using a chemical oxidant,and the resulting layer on graphite was shown to exhibit metallic-like spectroscopy curves when probed with current-sensing AFM. This technique also revealed current maps of the surface of the molecular materi- al. Fibre formation not only takes place on the graphite surface: nanometre scale rods have been imaged by using TEM on a grid after evaporation of solutions of the compounds in chloro- form. Molecular modelling proves the importance of the hydrogen bonds in the generation of the fibres,and indi- cates that the constitution of the mole- cules is vital for the formation of the desired columnar stacks,results that are consistent with the images obtained by microscopic techniques. The results show the power of noncovalent bonds in self-assembly processes that can lead to electrically conducting nanoscale supramolecular wires.

Chromophores in phenylenevinylene-based conjugated polymers: role of conformational kinks and chemical defects.

Abstract: The influence of chemical defects and conformational kinks on the nature of the lowest electronic excitations in phenylenevinylene-based polymers is assessed at the semiempirical quantum-chemical level. The amount of excited-state localization and the amplitude of through-space (Coulomb-like) versus through-bond (charge-transfer-like) interactions have been quantified by comparing the results provided by excitonic and supermolecular models. While excitation delocalization among conjugated segments delineated by the defects occurs in the acceptor configuration, self-confinement on individual chromophores follows from geometric relaxation in the excited-state donor configuration. The extent of excited-state localization is found to be sensitive to both the nature of the defect and the length of the conjugated chains. Implications for resonant energy transfer along conjugated polymer chains are discussed.

Einstein-Podolsky-Rosen correlations between two uniformly accelerated oscillators

Abstract: We consider the quantum correlations, i.e. the entanglement, between two systems uniformly accelerated with identical acceleration $a$ in opposite Rindler quadrants which have reached thermal equilibrium with the Unruh heat bath. To this end we study an exactly soluble model consisting of two oscillators coupled to a massless scalar field in $1+1$ dimensions. We find that for some values of the parameters the oscillators get entangled shortly after the moment of closest approach. Because of boost invariance there are an infinite set of pairs of positions where the oscillators are entangled. The maximal entanglement between the oscillators is found to be approximately 1.4 entanglement bits.