Showing papers by "Université catholique de Louvain published in 2000"

Ultrathin polymer coatings by complexation of polyelectrolytes at interfaces: suitable materials, structure and properties

Abstract: The article presents the state-of-the-art of alternating physisorption of oppositely charged polyelectrolytes, the so-called "layer-by-layer" method or "electrostatic self-assembly" (ESA), for the preparation of thin polymer coatings. In comparison to other, more established self-organization techniques, this recent method is distinguished by its simplicity, versatility, and speed. In particular, the tendency for self-healing is unique. Emphasis is given to the role of the molecular structure of the polyelectrolytes, and to the nature of the support. Also, various parameters for the preparation of multilayer films are highlighted, which are very important due to the kinetic control of the build-up process. The structure of the resulting coatings, their quality and stability, chemical reactions in the films, and potential applications are discussed.

A general methodology for bootstrapping in non-parametric frontier models

Abstract: The Data Envelopment Analysis method has been extensively used in the literature to provide measures of firms' technical efficiency. These measures allow rankings of firms by their apparent performance. The underlying frontier model is non-parametric since no particular functional form is assumed for the frontier model. Since the observations result from some data-generating process, the statistical properties of the estimated efficiency measures are essential for their interpretations. In the general multi-output multi-input framework, the bootstrap seems to offer the only means of inferring these properties (i.e. to estimate the bias and variance, and to construct confidence intervals). This paper proposes a general methodology for bootstrapping in frontier models, extending the more restrictive method proposed in Simar & Wilson (1998) by allowing for heterogeneity in the structure of efficiency. A numerical illustration with real data is provided to illustrate the methodology.

Assembly and function of type iii secretory systems

Abstract: Type III secretion systems allow Yersinia spp., Salmonella spp., Shigella spp., Bordetella spp., and Pseudomonas aeruginosa and enteropathogenic Escherichia coli adhering at the surface of a eukaryotic cell to inject bacterial proteins across the two bacterial membranes and the eukaryotic cell membrane to destroy or subvert the target cell. These systems consist of a secretion apparatus, made of approximately 25 proteins, and an array of proteins released by this apparatus. Some of these released proteins are "effectors," which are delivered into the cytosol of the target cell, whereas the others are "translocators," which help the effectors to cross the membrane of the eukaryotic cell. Most of the effectors act on the cytoskeleton or on intracellular-signaling cascades. A protein injected by the enteropathogenic E. coli serves as a membrane receptor for the docking of the bacterium itself at the surface of the cell. Type III secretion systems also occur in plant pathogens where they are involved both in causing disease in susceptible hosts and in eliciting the so-called hypersensitive response in resistant or nonhost plants. They consist of 15-20 Hrp proteins building a secretion apparatus and two groups of effectors: harpins and avirulence proteins. Harpins are presumably secreted in the extracellular compartment, whereas avirulence proteins are thought to be targeted into plant cells. Although a coherent picture is clearly emerging, basic questions remain to be answered. In particular, little is known about how the type III apparatus fits together to deliver proteins in animal cells. It is even more mysterious for plant cells where a thick wall has to be crossed. In spite of these haunting questions, type III secretion appears as a fascinating trans-kingdom communication device.

Requirements engineering in the year 00: a research perspective

Abstract: Requirements engineering (RE) is concerned with the identification of the goals to be achieved by the envisioned system, the operationalization of such goals into services and constraints, and the assignment of responsibilities for the resulting requirements to agents such as humans, devices, and software. The processes involved in RE include: domain analysis, elicitation, specification, assessment, negotiation, documentation, and evolution. Getting high quality requirements is difficult and critical. Recent surveys have confirmed the growing recognition of RE as an area of utmost importance in software engineering research and practice. The paper presents a brief history of the main concepts and techniques developed to date to support the RE task, with a special focus on modeling as a common denominator to all RE processes. The initial description of a complex safety-critical system is used to illustrate a number of current research trends in RE-specific areas such as goal oriented requirements elaboration, conflict management, and the handling of abnormal agent behaviors. Opportunities for goal based architecture derivation are also discussed together with research directions to let the field move towards more disciplined habits.

The Emotional Side of Prejudice: The Attribution of Secondary Emotions to Ingroups and Outgroups

Abstract: If people favor their ingroup, are especially concerned with their own group, and attribute different essences to different groups, it follows that their essence must be superior to the essence of other groups. Intelligence, language, and certain emotions are all considered to be distinctive elements of human nature or Essence. The role of intelligence and language in discrimination, prejudice, and racism has already been largely investigated, and this article focuses oil attributed emotions. Specifically, we investigate the idea that secondary emotions are typically human characteristics, and as such, they should be especially associated with and attributed to the ingroup. Secondary emotions may even be Jellied to outgroups. These differential associations and attributions of specifically human emotions to ingroups versus outgroups should affect intergroup relations. Results from several initial experiments are summarized that support our reasoning. This emotional approach to prejudice and racism is contrasted with more classic, cognitive perspectives.

The N170 occipito-temporal component is delayed and enhanced to inverted faces but not to inverted objects: an electrophysiological account of face-specific processes in the human brain

Abstract: Behavioral studies have shown that picture-plane inversion impacts face and object recognition differently, thereby suggesting face-specific processing mechanisms in the human brain. Here we used event-related potentials to investigate the time course of this behavioral inversion effect in both faces and novel objects. ERPs were recorded for 14 subjects presented with upright and inverted visual categories, including human faces and novel objects (Greebles). A N170 was obtained for all categories of stimuli, including Greebles. However, only inverted faces delayed and enhanced N170 (bilaterally). These observations indicate that the N170 is not specific to faces, as has been previously claimed. In addition, the amplitude difference between faces and objects does not reflect face-specific mechanisms since it can be smaller than between non-face object categories. There do exist some early differences in the time-course of categorization for faces and non-faces across inversion. This may be attributed either to stimulus category per se (e.g. face-specific mechanisms) or to differences in the level of expertise between these categories.

An extended model for void growth and coalescence

Abstract: A model for the axisymmetric growth and coalescence of small internal voids in elastoplastic solids is proposed and assessed using void cell computations. Two contributions existing in the literature have been integrated into the enhanced model. The first is the model of Gologanu-Leblond-Devaux, extending the Gurson model to void shape effects. The second is the approach of Thomason for the onset of void coalescence. Each of these has been extended heuristically to account for strain hardening. In addition, a micromechanically-based simple constitutive model for the void coalescence stage is proposed to supplement the criterion for the onset of coalescence. The fully enhanced Gurson model depends on the flow properties of the material and the dimensional ratios of the void-cell representative volume element. Phenomenological parameters such as critical porosities are not employed in the enhanced model. It incorporates the effect of void shape, relative void spacing, strain hardening, and porosity. The effect of the relative void spacing on void coalescence, which has not yet been carefully addressed in the literature. has received special attention. Using cell model computations, accurate predictions through final fracture have been obtained for a wide range of porosity, void spacing, initial void shape, strain hardening, and stress triaxiality. These predictions have been used to assess the enhanced model. (C) 2000 Elsevier Science Ltd. All rights reserved.

Handling obstacles in goal-oriented requirements engineering

Abstract: Requirements engineering is concerned with the elicitation of high-level goals to be achieved by the envisioned system, the refinement of such goals and their operationalization into specifications of services and constraints and the assignment of responsibilities for the resulting requirements to agents such as humans, devices and software. Requirements engineering processes often result in goals, requirements, and assumptions about agent behavior that are too ideal; some of them are likely not to be satisfied from time to time in the running system due to unexpected agent behavior. The lack of anticipation of exceptional behaviors results in unrealistic, unachievable, and/or incomplete requirements. As a consequence, the software developed from those requirements will not be robust enough and will inevitably result in poor performance or failures, sometimes with critical consequences on the environment. This paper presents formal techniques for reasoning about obstacles to the satisfaction of goals, requirements, and assumptions elaborated in the requirements engineering process. The techniques are based on a temporal logic formalization of goals and domain properties; they are integrated into an existing method for goal-oriented requirements elaboration with the aim of deriving more realistic, complete, and robust requirements specifications. A key principle is to handle exceptions at requirements engineering time and at the goal level, so that more freedom is left for resolving them in a satisfactory way. The various techniques proposed are illustrated and assessed in the context of a real safety-critical system.

Efficacy and Safety of Daily Risedronate in the Treatment of Corticosteroid-Induced Osteoporosis in Men and Women: A Randomized Trial*

Abstract: Long-term use of high-dose corticosteroids often results in bone loss, which may lead to osteoporosis-related fractures. This was a multicenter, double-blind study in which 290 ambulatory men and women receiving high-dose oral corticosteroid therapy (prednisone greater than or equal to 7.5 mg/day or equivalent) for 6 or more months were randomized to receive placebo, risedronate 2.5 mg/day, or risedronate 5 mg/day for 12 months. All patients received calcium 1 g and vitamin D 400 IU daily. The primary endpoint was lumbar spine bone mineral density (BMD) at month 12, Additional measurements included BMD at the femoral neck and trochanter and the incidence of vertebral fractures, Overall, there were statistically significant treatment effects on BMD at 12 months at the lumbar spine (p < 0.001), femoral neck (p = 0.004), and trochanter (p = 0.010), Risedronate 5 mg increased BMD at 12 months by a mean (SEM) of 2.9% (0.49%) at the lumbar spine, 1.8% (0.46%) at the femoral neck, and 2.4% (0.54%) at the trochanter, whereas BMD was maintained only in the control group, Although not powered to show fracture efficacy, we observed a reduction in the incidence of vertebral fractures of 70% in the combined risedronate treatment groups, relative to placebo (p = 0.042), Risedronate was well tolerated, had a good safety profile, and was not associated with gastrointestinal adverse events. We conclude that risedronate increases BMD and potentially reduces the incidence of vertebral fractures in patients,vith corticosteroid-induced osteoporosis.

Land‐Cover‐Change Trajectories in Southern Cameroon

Abstract: The objective of this study is to better understand the complexity of deforestation processes in southern Cameroon by testing a multivariate, spatial model of land-cover change trajectories associated with deforestation. The spatial model integrates a spectrum of independent variables that characterize land rent on a spatially explicit basis. The use of a time series of high-spatial-resolution remote sensing images (Landsat MSS and SPOT XS), spanning two decades, allows a thorough validation of spatial projections of future deforestation. Remote sensing observations reveal a continuous trend of forest clearing and forest degradation in southern regions of Cameroon, but with a highly fluctuating rate. A significant proportion of the areas subject to a land-cover conversion experienced other changes in the following years. The study also demonstrates that modeling land-cover change trajectories over several observation years allows a better projection of areas with a high probability of change in land-cover than projecting such areas on the basis of observations from the previous time period alone. Statistical results suggest that, in our southern Cameroon study area, roads mostly increased the accessibility of the forest for migrants rather than providing incentives for a transformation of local subsistence agriculture into market-oriented farming systems. The spacial model developed in this study allows simulations of likely impacts of human actions, leading to a transformation of the landscape (e.g., road projects) on key landscape attributes (e.g., biodiversity). Currently, several road projects or major logging concessions exist in southern Cameroon.

X-linked Alport Syndrome Natural History in 195 Families and Genotype- Phenotype Correlations in Males

Abstract: Alport syndrome (AS) is a type IV collagen hereditary disease characterized by the association of progressive hematuric nephritis, hearing loss, and, frequently, ocular changes. Mutations in the COL4A5 collagen gene are responsible for the more common X-linked dominant form of the disease. Considerable allelic heterogeneity has been observed. A "European Community Alport Syndrome Concerted Action" has been established to delineate accurately the AS phenotype and to determine genotype-phenotype correlations in a large number of families. Data concerning 329 families, 250 of them with an X-linked transmission, were collected. Characteristics of the 401 male patients belonging to the 195 families with COL4A5 mutation are presented. All male patients were hematuric, and the rate of progression to end-stage renal failure and deafness was mutation-dependent. Large deletions, non-sense mutations, or small mutations changing the reading frame conferred to affected male patients a 90% probability of developing end-stage renal failure before 30 yr of age, whereas the same risk was of 50 and 70%, respectively, in patients with missense or splice site mutation. The risk of developing hearing loss before 30 yr of age was approximately 60% in patients with missense mutations, contrary to 90% for the other types of mutations. The natural history of X-linked AS and correlations with COL4A5 mutations have been established in a large cohort of male patients. These data could be used for further evaluation of therapeutic approaches.

New metallic allotropes of planar and tubular carbon

Abstract: We propose a new family of layered sp(2)-like carbon crystals, incorporating five-, six-, and seven-membered rings in 2D Bravais lattices. These periodic sheets can be rolled so as to generate nanotubes of different diameter and chirality. We demonstrate that these sheets and tubes are metastable and more favorable than C-60, and it is also shown that their mechanical properties are similar to those of graphene. Density of states calculations of all structures revealed an intrinsic metallic behavior, independent of orientation, tube diameter, and chirality.

Coalescence of Single-Walled Carbon Nanotubes

Abstract: The coalescence of single-walled nanotubes is studied in situ under electron irradiation at high temperature in a transmission electron microscope. The merging process is investigated at the atomic level, using tight-binding molecular dynamics and Monte Carlo simulations. Vacancies induce coalescence via a zipper-like mechanism, imposing a continuous reorganization of atoms on individual tube lattices along adjacent tubes. Other topological defects induce the polymerization of tubes. Coalescence seems to be restricted to tubes with the same chirality, explaining the low frequency of occurrence of this event.

Hemispheric Asymmetries for Whole-Based and Part-Based Face Processing in the Human Fusiform Gyrus

Abstract: Behavioral studies indicate a right hemisphere advantage for processing a face as a whole and a left hemisphere superiority for processing based on face features. The present PET study identifies the anatomical localization of these effects in well-defined regions of the middle fusiform gyri of both hemispheres. The right middle fusiform gyrus, previously described as a face-specific region, was found to be more activated when matching whole faces than face parts whereas this pattern of activity was reversed in the left homologous region. These lateralized differences appeared to be specific to faces since control objects processed either as wholes or parts did not induce any change of activity within these regions. This double dissociation between two modes of face processing brings new evidence regarding the lateralized localization of face individualization mechanisms in the human brain.

Endoscopic cordectomy. A proposal for a classification by the Working Committee, European Laryngological Society.

Abstract: The European Laryngological Society is proposing a classification of different laryngeal endoscopic cordectomies in order to ensure better definitions of post-operative results. We chose to keep the word "cordectomy" even for partial resections because it is the term most often used in the surgical literature. The classification comprises eight types of cordectomies: a subepithelial cordectomy (type I), which is resection of the epithelium; a subligamental cordectomy (type II), which is a resection of the epithelium, Reinke's space and vocal ligament; transmuscular cordectomy (type III), which proceeds through the vocalis muscle; total cordectomy (type IV); extended cordectomy, which encompasses the contralateral vocal fold and the anterior commissure (type Va); extended cordectomy, which includes the arytenoid (type Vb); extended cordectomy, which encompasses the subglottis (type Vc); and extended cordectomy, which includes the ventricle (type Vd). Indications for performing those cordectomies may vary from surgeon to surgeon. The operations are classified according to the surgical approach used and the degree of resection in order to facilitate use of the classification in daily practice. Each surgical procedure ensures that a specimen is available for histopathological examination.

Neuroanatomical Substrates of Arabic Number Processing, Numerical Comparison, and Simple Addition: A PET Study

Abstract: Positron emission tomography was used to localize the cerebral networks specifically involved in three basic numerical processes: arabic numeral processing, numerical magnitude comparison, and retrieval of simple addition facts. Relative cerebral blood flow changes were measured while normal volunteers were resting with eyes closed, making physical judgment on nonnumerical characters or arabic digits, comparing, or adding the same digits. Processing arabic digits bilaterally produced a large nonspecific activation of occipito-parietal areas, as well as a specific activation of the right anterior insula. Comparison and simple addition fact retrieval revealed a fronto-parietal network involving mainly the left intraparietal sulcus, the superior parietal lobule and the precentral gyrus. Comparison also activated, but to a lesser extent, the right superior parietal lobe, whereas addition also activated the orbito-frontal areas and the anterior insula in the right hemisphere. Implications for current anatomo-functional models of numerical cognition are drawn.

Congenital Hereditary Lymphedema Caused by a Mutation That Inactivates VEGFR3 Tyrosine Kinase

Abstract: Hereditary lymphedema is a chronic swelling of limbs due to dysfunction of lymphatic vessels. An autosomal dominant, congenital form of the disease, also known as "Milroy disease," has been mapped to the telomeric part of chromosome 5q, in the region 5q34-q35. This region contains a good candidate gene for the disease, VEGFR3 (FLT4), that encodes a receptor tyrosine kinase specific for lymphatic vessels. To clarify the role of VEGFR3 in the etiology of the disease, we have analyzed a family with hereditary lymphedema. We show linkage of the disease with markers in 5q34-q35, including a VEGFR3 intragenic polymorphism, and we describe an A-->G transition that cosegregates with the disease, corresponding to a histidine-to-arginine substitution in the catalytic loop of the protein. In addition, we show, by in vitro expression, that this mutation inhibits the autophosphorylation of the receptor. Thus, defective VEGFR3 signaling seems to be the cause of congenital hereditary lymphedema linked to 5q34-q35.

Isolation of Adherent Polycyclic Aromatic Hydrocarbon (PAH)-Degrading Bacteria Using PAH-Sorbing Carriers

Abstract: Two different procedures were compared to isolate polycyclic aromatic hydrocarbon (PAH)-utilizing bacteria from PAH-contaminated soil and sludge samples, i.e., (i) shaken enrichment cultures in liquid mineral medium in which PAHs were supplied as crystals and (ii) a new method in which PAH degraders were enriched on and recovered from hydrophobic membranes containing sorbed PAHs. Both techniques were successful, but selected from the same source different bacterial strains able to grow on PAHs as the sole source of carbon and energy. The liquid enrichment mainly selected for Sphingomonas spp., whereas the membrane method exclusively led to the selection of Mycobacterium spp. Furthermore, in separate membrane enrichment set-ups with different membrane types, three repetitive extragenic palindromic PCR-related Mycobacterium strains were recovered. The new Mycobacterium isolates were strongly hydrophobic and displayed the capacity to adhere strongly to different surfaces. One strain, Mycobacterium sp. LB501T, displayed an unusual combination of high adhesion efficiency and an extremely high negative charge. This strain may represent a new bacterial species as suggested by 16S rRNA gene sequence analysis. These results indicate that the provision of hydrophobic sorbents containing sorbed PAHs in the enrichment procedure discriminated in favor of certain bacterial characteristics. The new isolation method is appropriate to select for adherent PAH-degrading bacteria, which might be useful to biodegrade sorbed PAHs in soils and sludge.

Power can bias impression processes: Stereotyping subordinates by default and by design.

Abstract: Powerholders may engage in two stereotyping processes: (a) by default, inattention to stereotype-inconsistent information, due to lack of dependency, and (b) by design, effortful attention to stereotype-consistent information, due to explicit control. Study 1 manipulated control (not dependency) over internship applicants; powerful decision-makers increased attention to stereotypic attributes, consistent with stereotyping by design. Study 2 measured differences in trait dominance as an analog to situational control, replicating Study 1. Study 3 separately manipulated perceiver control and dependency; powerful perceivers increased attention to powerless targets’ stereotypic attributes (by design) and also decreased attention to counter-stereotypic attributes (by default). Study 4 compared powerful perceivers’ ratings of potential subordinates to their own prior ratings of target categories and target traits. Relative to the powerless, powerful perceivers’ impressions were based significantly less on target traits, supporting the attention results.

Wavelet processes and adaptive estimation of the evolutionary wavelet spectrum

Abstract: This article defines and studies a new class of non-stationary random processes constructed from discrete non-decimated wavelets which generalizes the Cramer (Fourier) representation of stationary time series. We define an evolutionary wavelet spectrum (EWS) which quantifies how process power varies locally over time and scale. We show how the EWS may be rigorously estimated by a smoothed wavelet periodogram and how both these quantities may be inverted to provide an estimable time-localized autocovariance. We illustrate our theory with a pedagogical example based on discrete non- decimated Haar wavelets and also a real medical time series example.

O-2 reduction in PEM fuel cells: Activity and active site structural information for catalysts obtained by the pyrolysis at high temperature of Fe precursors

Abstract: Catalytic activity for O-2 electroreduction in acidic medium has been studied. Catalysts have been produced by pyrolyzing perylene tetracarboxylic dianhydride (PTCDA) combined with Fe and N precursors. The Fe precursors used in this work are either Fe-II acetate or Cl-Fe-III Tetramethoxyphenyl porphyrin (Cl-FeTMPP). The N precursors are NH3 and/or Cl-FeTMPP. To be able to vary the catalytic activity, two synthesis procedures have been used, varying either the heat-treatment temperature or the Fe content of the pyrolyzed materials. All the catalysts have been studied by Time-of-Flight Secondary Ion Mass Spectrometry (ToF SIMS) in order to find out if the relative intensity of one or several secondary ions was following the changes observed in the catalytic activity. Only one ion, FeN2C4+, may be considered as the signature of the catalytic site generated in this work. It has been detected in all prepared catalysts, whatever the Fe precursor or the synthesis procedure was used. It is proposed that this ion is produced under ToF SIMS analysis from part of a 1,10 phenanthrolinic-type structure, which is itself part of the catalytic site. This catalytic site is probably the same as the one obtained by the pyrolysis at high temperature (greater than or equal to 800 degreesC) of N-4-Fe macrocycles adsorbed on carbon black. RDE and PEM fuel cell tests demonstrate that the most performing catalysts are those containing 2 wt % Fe as Cl-FeTMPP and 0.2 wt % Fe as Fe acetate. Increasing the Fe content beyond these limits mainly generates catalytically inactive Fe clusters and interferes with the characterization of the high-temperature active site.

Sensitivity Analysis of Values at Risk

Abstract: The aim of this paper is to analyze the sensitivity of Value at Risk (VaR) with respect to portfolio allocation. We derive analytical expressions for the first and second derivatives of the Value at Risk, and explain how they can be used to simplify statistical inference and to perform a local analysis of the Value at Risk. An empirical illustration of such an analysis is given for an portfolio of French stocks.

Transcription factor hepatocyte nuclear factor 6 regulates pancreatic endocrine cell differentiation and controls expression of the proendocrine gene ngn3.

Abstract: Hepatocyte nuclear factor 6 (HNF-6) is the prototype of a new class of cut homeodomain transcription factors. During mouse development, HNF-6 is expressed in the epithelial cells that are precursors of the exocrine and endocrine pancreatic cells. We have investigated the role of HNF-6 in pancreas differentiation by inactivating its gene in the mouse. In hnf6(-/-) embryos, the exocrine pancreas appeared to be normal but endocrine cell differentiation was impaired. The expression of neurogenin 3 (Ngn-3), a transcription factor that is essential for determination of endocrine cell precursors, was almost abolished. Consistent with this, we demonstrated that HNF-6 binds to and stimulates the ngn3 gene promoter. At birth, only a few endocrine cells were found and the islets of Langerhans were missing. Later, the number of endocrine cells increased and islets appeared. However, the architecture of the islets was perturbed, and their beta cells were deficient in glucose transporter 2 expression. Adult hnf6(-/-) mice were diabetic. Taken together, our data demonstrate that HNF-6 controls pancreatic endocrine differentiation at the precursor stage and identify HNF-6 as the first positive regulator of the proendocrine gene ngn3 in the pancreas. They also suggest that HNF-6 is a candidate gene for diabetes mellitus in humans.