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See detailOn the substrate specificity of bacterial DD-peptidases: evidence from two series of peptidoglycan-mimetic peptides
Anderson, J. W.; Adediran, S. A.; Charlier, Paulette ULg et al

in Biochemical Journal (2003), 373(Part 3), 949-955

The reactions between bacterial DD-peptidases and beta-lactam antibiotics have been studied for many years. Less well understood are the interactions between these enzymes and their natural substrates ... [more ▼]

The reactions between bacterial DD-peptidases and beta-lactam antibiotics have been studied for many years. Less well understood are the interactions between these enzymes and their natural substrates, presumably the peptide moieties of peptidoglycan. In general, remarkably little activity has previously been demonstrated in vitro against potential peptide substrates, although in many cases the peptides employed were non-specific and not homologous with the relevant peptidoglycan. In this paper, the specificity of a panel of DD-peptidases against elements of species-specific D-alanyl-D-alanine peptides has been assessed. In two cases, those of soluble, low-molecular-mass DD-peptidases, high activity against the relevant peptides has been demonstrated. In these cases, the high specificity is towards the free N-terminus of the peptidoglycan fragment. With a number of other enzymes, particularly high-molecular-mass DD-peptidases, little or no activity against these peptides was observed. In separate experiments, the reactivity of the enzymes against the central, largely invariant, peptide stem was examined. None of the enzymes surveyed showed high activity against this structural element although weak specificity in the expected direction towards the one structural variable (D-gammaGln versus D-gammaGlu) was observed. The current state of understanding of the activity of these enzymes in vitro is discussed. [less ▲]

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See detailOn the symmetry of the age field of a passive tracer released into a one-dimensional fluid flow by a point-source
Deleersnijder, E.; Delhez, Eric ULg; Crucifix, M. et al

in Bulletin de la Société Royale de Liège (2001), 70

Tracer is released from a point-source into an incompressible, one-dimensional fluid flow, with constant velocity and diffusivity. The age of a tracer parcel, which is defined as the time elapsed since ... [more ▼]

Tracer is released from a point-source into an incompressible, one-dimensional fluid flow, with constant velocity and diffusivity. The age of a tracer parcel, which is defined as the time elapsed since leaving the source, may be evaluated as the ratio of the age concentration to the tracer concentration. The latter are governed by two partial differential equations. Time-dependent analytical solutions are derived, which show that the age is symmetric with respect to the source. This is astonishing, since it could have been expected that the age would reflect somehow the strong asymmetry of the tracer concentration, which tends to be much larger on the downstream side of the source than on the upstream side. Some finite-difference counterparts of this problem are seen to lead to age fields which, in their steady-state limit, are also symmetric with respect to the source. This is believed to be helpful to interpret the results of numerical models of complex fluid flows in which the age is introduced as a diagnostic variable. [less ▲]

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See detailOn the TEC short-term forecast with corrections based on the average ionospheric response to background and storm-time geomagnetic conditions
Stankov, Stanimir; Warnant, René ULg; Kozarev, R.

in Geophysical Research Abstracts (2009, April), 11(Abs. No EGU2009-13283),

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See detailOn the transferability of concepts and its significance for landscape ecology.
Bogaert, Jan ULg; Barima, Y S S

in JME : Journal of Mediterranean Ecology (2008), 9

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See detailOn the ultimate compressive strength of transversely cracked plates
Bayatfar, Abbas ULg; Pire, Timothée ULg; Rigo, Philippe ULg

in Proceedings of the ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering (2014, June)

This paper aims to numerically analyse the ultimate strength of transversely cracked steel plates under longitudinal compressive loading, considering the effect of initial distortion as well. The main ... [more ▼]

This paper aims to numerically analyse the ultimate strength of transversely cracked steel plates under longitudinal compressive loading, considering the effect of initial distortion as well. The main objective of this study is to investigate the ultimate compressive strength characteristics of an unstiffened steel plate due to transverse cracking damages located in the middle (i.e. centre cracks and edge cracks). To achieve that, a series of non-linear finite element (FE) analyses are carried out using ANSYS commercial finite element code. The obtained FE results are discussed to indicate the amount of crack influence, in terms of its length and location, on the ultimate compressive strength of a steel plate element with different thicknesses. [less ▲]

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See detailOn the understanding of the physical changes in inulin powder as a function of water activity.
Ronkart, Sébastien; Paquot, Michel ULg; Goffin, Dorothée ULg et al

Poster (2006, December)

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See detailOn the use and computation of likelihood ratios in clinical chemistry.
Albert, Adelin ULg

in Clinical Chemistry (1982), 28(5), 1113-9

The clinical relevance of likelihood ratios (L-values) for revising the physician's diagnostic probabilities has been recognized. However, the calculation of L-values, particularly in the case of ... [more ▼]

The clinical relevance of likelihood ratios (L-values) for revising the physician's diagnostic probabilities has been recognized. However, the calculation of L-values, particularly in the case of quantitative or mixed quantitative-binary test results, raises problems that have not yet been addressed. Based on a very general assumption that yields a simple functional form for the likelihood ratio, a method is developed that allows such calculations regardless of the nature and the number of clinical laboratory tests to be interpreted simultaneously. Hence the notion of predictive value (posterior probability) is extended from binary or dichotomized tests to quantitative tests, and from univariate to multivariate clinical laboratory results. The simplicity and flexibility of this approach eliminates difficulties in computation arising from the addition of new data to an existing data base. It is hoped that this method will now allow L-values to be reported along with the original test results in daily laboratory practice. [less ▲]

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See detailOn the use of a diffusion model for acoustically coupled rooms
Billon, Alexis ULg; Valeau, Vincent; Sakout, Anas et al

in Journal of the Acoustical Society of America (2006), 120(4), 2043-2054

A numerical model is proposed to predict the reverberant sound field in a system of two coupled volumes that are connected through an open aperture. The model is based on the numerical implementation of a ... [more ▼]

A numerical model is proposed to predict the reverberant sound field in a system of two coupled volumes that are connected through an open aperture. The model is based on the numerical implementation of a diffusion model that has already been applied to predict the sound-energy distribution and the sound decay in single rooms. In comparison with the statistical theory, the proposed approach permits the prediction of the sound field by taking into account the sound source location and the receiver locations as well as the transition from one room to the other at the coupling aperture. Moreover, the diffusion model results match satisfactorily the experimental data in terms of sound-pressure level and reverberation times, both in the room containing the source and in the receiving room. Simulations with a ray-based model are also carried out, leading to results similar to those of the diffusion model, but at a cost of larger computation times. [less ▲]

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See detailOn the use of a truly–mixed formulation in topology optimization with global stress–constraints
Bruggi, Matteo; Duysinx, Pierre ULg

in Proceeding of the 8th World Congress on Structural and Multidisciplinary Optimization (2009, June)

The work refers to the field of topology optimization for bidimensional structures and addresses the case in which global stress–constraints are considered to improve final designs. Most of the previous ... [more ▼]

The work refers to the field of topology optimization for bidimensional structures and addresses the case in which global stress–constraints are considered to improve final designs. Most of the previous research tackles this topic relying on classical displacement–based finite elements where stresses are recovered via post–processing techniques. The work conversely investigates the use of a truly–mixed formulation where stresses are independent variables of the problem while displacements play the secondary role of Lagrangian multiplier. The implemented discretization is based on a composite triangular element whose features may be advantageously exploited in stress–constrained topology optimization. The discretization is checkerboard–free and allows to tackle topology optimization with element–based constraints without introducing any additional filtering technique. The high accuracy in the evaluation of the average stresses is expected to improve the efficiency of the numerical procedure, especially in the case of a single global constraint that has to govern the whole domain. The adopted discretization also passes the robustness condition even in the case of incompressible materials and this allows to menage strength constraints also for rubber–like components. Basing on these ideas, numerical investigations are carried out to test preliminary applications of the truly–mixed technique coupled with topology optimization and global stress–constraints. To handle the well–known singularity problem, that affects the constraints imposition, an alternative scheme is herein adopted instead of a classical "–relaxation. An example where a homogenous stress distribution is expected is firstly tested, having the aim of pointing out the main features of the proposed procedure. Afterwards, numerical simulations address a classical L–shaped specimen, pointing out pros and cons of the approach. [less ▲]

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See detailOn the use of adhesion parameters to validate models specified using systems of affine differential equations
Jaeger, Jonathan ULg; Lambert, Philippe ULg

E-print/Working paper (2012)

A strategy for the selection of system of differential equations is proposed based on Bayesian ODE-penalized B-spline approach. It estimates the ODE parameters, approximates the solution of the ODE model ... [more ▼]

A strategy for the selection of system of differential equations is proposed based on Bayesian ODE-penalized B-spline approach. It estimates the ODE parameters, approximates the solution of the ODE model and quantifies the suitability of the proposed differential equations to model the dynamics of the observed state functions. Simulation study confirms that these ODE-adhesion parameters are able to question a system of differential equations as a descriptor of the dynamics in the state functions. This methodology is illustrated on a pharmacokinetic study. [less ▲]

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See detailOn the Use of Automata-based Techniques in Symbolic Model Checking: invited address
Legay, Axel; Wolper, Pierre ULg

in Electronic Notes in Theoretical Computer Science (2006, March 09), 150(1), 3-8

Checking infinite-state systems is frequently done by encoding infinite sets of states as regular languages. Computing such a regular representation of, say, the reachable set of states of a system ... [more ▼]

Checking infinite-state systems is frequently done by encoding infinite sets of states as regular languages. Computing such a regular representation of, say, the reachable set of states of a system requires acceleration techniques that can finitely compute the effect of an unbounded number of transitions. Among the acceleration techniques that have been proposed, one finds both specific and generic techniques. Specific techniques exploit the particular type of system being analyzed, e.g. a system manipulating queues or integers, whereas generic techniques only assume that the transition relation is represented by a finite-state transducer, which has to be iterated. In this paper, we survey two generic techniques that have been presented in [B. Boigelot and A. Legay and P. Wolper, Iterating Transducers in the Large, Proc. 15th Int. Conf. on Computer Aided Verification, Boulder, USA, Lecture Notes in Computer Science, volume 2725, year 2003, pages 223–235] and [B. Boigelot and A. Legay and P. Wolper, Omega-Regular Model Checking, Proc. 10th Int. Conf. on Tools and and Algorithms for the Construction and Analysis of Systems, Barcelona, Spain, Lecture Notes in Computer Science, volume 2988, year 2004, pages 561–575]. Those techniques build on earlier work, but exploits a number of new conceptual and algorithmic ideas, often induced with the help of experiments, that give it a broad scope, as well as good performance. [less ▲]

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See detailOn the use of Belgian Soil Map to predict risk of nitrate and pesticide lixiviation
Bah, Boubacar Billo ULg; Vandenberghe, Christophe ULg; Deneufbourg, Mathieu ULg et al

Poster (2014, February 26)

Pollution by nitrate and pesticides has impacts on drinking water reserves and aquatic systems. Nowadays, this problem is the key point of the European Policy with the implementation of the Water ... [more ▼]

Pollution by nitrate and pesticides has impacts on drinking water reserves and aquatic systems. Nowadays, this problem is the key point of the European Policy with the implementation of the Water Framework Directive (Directive 2000/60/EC). According to these legislations, Member States are supposed to take measures to limit environmental and toxicological effects caused by nitrate and pesticides use. This paper presents three different approaches allowing assessment of diffuse (non-point sources) pollution risks of water resources by nitrate and pesticides. The first approach consists on the interpretation of the geomorphopedological information (geologic substratum type, presence of karst phenomena, soil texture, natural drainage, profile development, type and percent of stoniness, soil thickness, …) provided by the Digital Soil Map of Wallonia. Soil physical characteristics are assessed in terms of soil water percolation/infiltration, runoff, pollutants retention, mineralization, and erosion. Second approach consists on the use of spatially distributed mechanistic models. Nitrate lixiviation from agricultural land to groundwater has been simulated from the SWAT model. Pesticide lixiviation from soil to groundwater has been predicted from the one-dimensional, dynamic, multi-layered model named PEARL (Pesticide Emission Assessment at Regional and Local scales). Model input parameters are mainly extracted from the existing soil physical and physico-chemical, crop and pesticides properties databases. Relevant soil parameters not directly available in existing databases, such as bulk density, hydraulic conductivity, potential evapotranspiration… have been derived from pedotransfers functions. Third approach consists on in situ lixiviation studies by the way of lysimeters. Concentrations measured at the bottom (2 m deep) of lysimeters represent a straight “index of risk” for groundwater and, on the other hand, allow the validation of simulation models used to predict nitrate and pesticides lixiviation risk under different scenarios. The Digital Soil Map of Wallonia, one of the core data source, allows the spatialisation of the predicted lixiviation risk at regional level, providing to the local authorities and the decision makers a tool for the identification of the areas at risk of pollution, where specific monitoring actions and prevention measures for the protection of waters can be implemented. [less ▲]

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See detailOn the use of carbon dioxide and vegetable oil for the synthesis of bio-based cyclic carbonates
Alves, Margot ULg; Tassaing, Thierry; Mereau, R. et al

Poster (2014, July 03)

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See detailOn the use of carbon dioxide and vegetable oil for the synthesis of bio-based cyclic carbonates
Alves, Margot ULg; Tassaing, Thierry; Méreau, Raphaël et al

Conference (2014, August 27)

The uncertain cost of petroleum and its expected depletion in the near future prompted the scientific community to search for new sources of carbon just inexpensive, abundant and easily exploitable ... [more ▼]

The uncertain cost of petroleum and its expected depletion in the near future prompted the scientific community to search for new sources of carbon just inexpensive, abundant and easily exploitable. Combining the use of renewable resources such as vegetable oils and carbon dioxide as a carbon source for the development of a sustainable chemistry is very promising. Thus, this research project fits within the framework of the chemical fixation of CO2 and the utilization of vegetable oils as a substitute for basic petroleum derivatives for the production of new monomers and new bio-based organic polymers. As a first step, the catalytic synthesis of cyclic carbonate monomers from CO2 and epoxidized vegetable oils (and/or the corresponding fatty esters) will be considered. The synthesis of non-isocyanates polyurethanes (NIPUS) will then be performed by reacting in bulk these new monomers with diamines under mild heating. In this talk, we will present the results that we have obtained on the first step of the process. Namely, we have investigated various catalytic platforms enabling the cycloaddition of CO2 on epoxidized oils in the most efficient way under mild conditions. For such task, in situ kinetic follow-up of this reaction has been performed by FT-IR or Raman spectroscopy in order to identify the best catalytic systems and to evaluate the influence of various parameters (pressure, temperature catalyst concentration, nature of epoxidized oil) on the yields and the reaction kinetics. Then, the most efficient catalytic systems have been investigated by molecular modeling in order to identify the key structural parameters of the catalyst that govern its efficiency. [less ▲]

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See detailOn the use of control surface excitation in flutter testing
Wright, Jan R; Wong, Jerry; Cooper, Jonathan E et al

in Proceedings of the Institution of Mechanical Engineers - Part G - Journal of Aerospace Engineering (2003), 217(6), 317-332

Flutter testing is aimed at demonstrating that the aircraft flight envelope is flutter free. Response measurements from deliberate excitation of the structure are used to identify and track frequency and ... [more ▼]

Flutter testing is aimed at demonstrating that the aircraft flight envelope is flutter free. Response measurements from deliberate excitation of the structure are used to identify and track frequency and damping values against velocity. In this paper, the common approach of using a flight control surface to provide the excitation is examined using a mathematical model of a wing and control surface whose rotation is restrained by a simple actuator. In particular, it is shown that it is essential to use the demand signal to the actuator as a reference signal for data processing. Use of the actuator force (or strain) or control angle (or actuator displacement) as a reference signal is bad practice because these signals contain response information. It may also be dangerous in that the onset of flutter may not be seen in the test results. [less ▲]

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See detailOn the use of control surface excitation in flutter testing
Wright, Jan R; Wong, Jerry; Cooper, Jonathan Edward et al

in Proceedings of the 2003 International Forum on Aeroelasticity and Structural Dynamics (2003, June)

Flutter testing is used to demonstrate that the aircraft flight envelope is flutter free. Response measurements from deliberate excitation of the structure are used to identify and track frequency and ... [more ▼]

Flutter testing is used to demonstrate that the aircraft flight envelope is flutter free. Response measurements from deliberate excitation of the structure are used to identify and track frequency and damping values against velocity. In this paper, the common approach of using a flight control surface to provide the excitation is examined us ing a mathematical model of a wing and control surface whose rotation is restrained by a simple actuator. In particular, it is shown that it is essential to use the demand signal to the actuator as a reference signal for data processing. Use of the actuator force (or strain) or control angle (or actuator displacement) as a reference signal is bad practice because these signals contain response information. It may also be dangerous in that the onset of flutter may not be seen in the test results. Control sur face flutter is of particular concern. [less ▲]

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See detailOn the use of Cowan Code for Atomic Structure Calculations in Singly Ionized Lanthanides
Quinet, Pascal ULg; Palmeri, P.; Biémont, Emile ULg

Conference (1998, August)

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See detailOn the use of diffusion equations to model the acoustics of coupled rooms
Billon, Alexis ULg; Valeau, Vincent; Picaut, Judicaël et al

in Journal of the Acoustical Society of America (2008), 123(5), 3910-3910

he acoustics of coupled rooms are characterized by energy exchanges through apertures and/or partition walls. The use of systems of diffusion equations allows to predict the temporal and spatial energy ... [more ▼]

he acoustics of coupled rooms are characterized by energy exchanges through apertures and/or partition walls. The use of systems of diffusion equations allows to predict the temporal and spatial energy distributions in these configurations quite accurately. In this presentation, the diffusion formalism for room acoustics-prediction is summarized. The systems of equations to be solved in the case of coupling through an aperture and through a partition wall are presented. For two rooms coupled through an aperture (two classrooms connected through an open door), the results obtained with the diffusion model are compared to experimental data, in terms of sound pressure levels and sound decays. On the other hand, for the case of two classrooms connected through a partition wall, the diffusion model is compared to experimental data in terms of sound pressure level difference only. Finally, an engineering application is presented in the configuration involving a workroom including multiple sound sources (e.g., machines) connected to offices through open and closed doors. [less ▲]

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