A framework for dynamic implicit curve approximation by an irregular discrete approach

The approximation of implicit planar curves by line segments is a very classical problem. Many algorithms use interval analysis to approximate this curve, and to handle the topology of the final reconstruction. In this article, we use discrete geometry tools to build an original geometrical and topological representation of the implicit curve. The polygonal approximation contains few segments, and the Reeb graph permits to sum up efficiently the shape and the topology of the curve. Furthermore, we propose two algorithms to process local cells refinement and local cells grouping schemes. We illustrate these schemes with a global system that efficiently handles manual or automatic fast updates on the global reconstruction, by considering topological or geometrical constraints. We also compare the speed and the quality of our approach with two classical methods.     

Automatic computation of pebble roundness using digital imagery and discrete geometry

The shape of sedimentary particles is an important property, from which geographical hypotheses related to abrasion, distance of transport, river behavior, etc. can be formulated. In this paper, we use digital image analysis, especially discrete geometry, to automatically compute some shape parameters such as roundness, i.e. a measure of how much the corners and edges of a particle have been worn away.In contrast to previous work in which traditional digital images analysis techniques, such as Fourier transform, are used, we opted for a discrete geometry approach that allowed us to implement Wadell's original index, which is known to be more accurate, but more time consuming to implement in the field.Our implementation of Wadell's original index is highly correlated (92%) with the roundness classes of Krumbein's chart, used as a ground-truth. In addition, we show that other geometrical parameters, which are easier to compute, can be used to provide good approximations of roundness.We also used our shape parameters to study a set of pebbles digital images taken from the Progo basin river network (Indonesia). The results we obtained are in agreement with previous work and open new possibilities for geomorphologists thanks to automatic computation.     

The other side of ranking schemes: generating weights for specified outcomes

This paper treats the problem of how to determine weights in a ranking, which will cause a selected entity to attain the highest possible position. We establish that there are two types of entities in a ranking scheme: those which can be ranked as number one and those which cannot. These two types of entities can be identified using the “ranking hull” of the data; a polyhedral set that envelops the data. Only entities with data points on the boundary of this hull can attain the number one position. There are no weights that will make an entity whose data point is in the interior of the hull to ever attain the number one position. We deal with these two types of entities separately. In the first case, we propose an approach for finding a set of weights that, under special conditions, will result in a selected entity achieving the top of the ranking without ties and without ignoring any of the attributes. For the second category of entities, we devise a procedure to guarantee that these entities will attain their highest possible position in the ranking. The first case will require using interior point methods to solve a linear program (LP). The second case involves a binary mixed integer formulation. These two mathematical programs were tested on data from a well‐known university ranking.     

FAST: acceleration from theory to practice

Fast acceleration of symbolic transition systems (Fast) is a tool for the analysis of systems manipulating unbounded integer variables. We check safety properties by computing the reachability set of the system under study. Even if this reachability set is not necessarily recursive, we use innovative techniques, namely symbolic representation, acceleration and circuit selection, to increase convergence. Fast has proved to perform very well on case studies. This paper describes the tool, from the underlying theory to the architecture choices. Finally, Fast capabilities are compared with those of other tools. A range of case studies from the literature is investigated. This paper is mainly based on results presented at CAV 2003, TACAS 2004 and ATVA 2005.     

Measuring Affective Clarity Indirectly: Individual Differences in Response Latencies of State.

This research investigated a new method to measure momentary affective clarity indirectly, which is based on latencies of responses to state affect items. Three studies revealed that this indirect measure of momentary clarity demonstrated high reliability and stability as well as convergent and predictive validity. The indirect measure was associated with dispositional clarity when the concept of clarity was activated before measuring response latencies (Studies 1 and 2) and was related to self-reports of momentary clarity (Study 3). Furthermore, Study 3 demonstrated that indirectly measured clarity decreased after an affectively complex film. Indirectly, but not directly, measured momentary clarity predicted a more positive affective state at the end of the study. This effect was mediated by affect regulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Physico-Chemical Characterizations of Poly(vinylidene fluoride)/Cu3(BTC)2 Composite Membranes Prepared by In Situ Crystal Growth

In this work, we present a simple and fast method for elaborating hybrid membranes by growing metal–organic framework crystals inside a polymer solution. The solution thus obtained was casted then annealed at 90°C for 5 h. This method was tested with poly(vinylidene fluoride) (PVDF) as a piezoelectric polymer and the Cu₃(BTC)₂, BTC = 1,3,5-benzene tricarboxylate, as a filler. The characterization of the obtained membranes by attenuated total reflectance Fourier transform infrared spectroscopy and X-ray diffraction showed the presence of the characteristic signatures of Cu₃(BTC)₂ and the β-phase of PVDF. Moreover, scanning electron microscopy images reveal that the Cu₃(BTC)₂ crystallites have grown along the PVDF membranes. The effect of the filler on both thermal and mechanical properties of the membranes was also studied. POLYM. ENG. SCI., 60:464–473, 2020. © 2019 Society of Plastics Engineers     

Effect of GABA,a Bacterial Metabolite,on Pseudomonas fluorescens Surface Properties and Cytotoxicity

Different bacterial species and, particularly Pseudomonas fluorescens, can produce gamma-aminobutyric acid (GABA) and express GABA-binding proteins. In this study, we investigated the effect of GABA on the virulence and biofilm formation activity of different strains of P. fluorescens. Exposure of a psychotropic strain of P. fluorescens (MF37) to GABA (10⁻⁵ M) increased its necrotic-like activity on eukaryotic (glial) cells, but reduced its apoptotic effect. Conversely, muscimol and bicuculline, the selective agonist and antagonist of eukaryote GABA_A receptors, respectively, were ineffective. P. fluorescens MF37 did not produce biosurfactants, and its caseinase, esterase, amylase, hemolytic activity or pyoverdine productions were unchanged. In contrast, the effect of GABA was associated to rearrangements of the lipopolysaccharide (LPS) structure, particularly in the lipid A region. The surface hydrophobicity of MF37 was marginally modified, and GABA reduced its biofilm formation activity on PVC, but not on glass, although the initial adhesion was increased. Five other P. fluorescens strains were studied, and only one, MFP05, a strain isolated from human skin, showed structural differences of biofilm maturation after exposure to GABA. These results reveal that GABA can regulate the LPS structure and cytotoxicity of P. fluorescens, but that this property is specific to some strains.     

Limitation of the Coalescence of Evolutive Droplets by the Use of Copolymers in a Thermoplastic/Thermoset Blend

Summary: Polystyrene (PS)/epoxy‐amine (DGEBA‐MDEA) is a thermoplastic/thermoset precursor blend which is miscible at high temperature (177 °C), and which phase separates under the polymerization of the epoxy‐amine system. Previous studies have shown that the morphology of this blend polymerized under shear is coarse and irregular because the dispersed epoxy‐amine domains coalesce before they gel. Several styrene‐methyl methacrylate and a styrene‐butadiene‐styrene block copolymers have been added to the PS/DGEBA‐MDEA 60/40 blend in order to limit the coalescence and thus obtain a finer morphology. Two of the copolymers used were reactive either with the epoxy or with the amine. It was shown that the addition of 15 wt.‐% of non reactive copolymer had a positive but limited effect on the size of the final epoxy‐amine particles. The copolymer remained at the interface at the early stages of the polymerization. However, it was pulled out by the shear forces around the gel point of the epoxy domains. Most of the non reactive copolymer was present in the shape of micelles at the end of the process. On the other hand, the reactive copolymers were able to establish covalent bonds with the epoxy‐amine drops and hence were not extracted at all. Consequently they allowed the decrease the size of the particles by a factor of 15. Despite this, the observation of the morphology at different stages of the polymerization has revealed that the copolymer moved at the interface of the epoxy domains during the collision of two droplets. The movements of fluids into the epoxy domains pushed the copolymer out of the inter‐droplet zone so that it could not prevent the drainage of the liquid film between the droplets and consequently their coalescence.

TEM showing that the layer of copolymer (in dark grey) has moved along the interface of epoxy‐amine drops during their successful collision in a polystyrene‐rich matrix.