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See detailOn the Role of Out-of-Equilibrium Microstructures in Ti-6Al-4V and in Stainless Steel 316L Processed by Selective Laser Melting in Determining their Mechanical Properties
Mertens, Anne ULg; Reginster, Sylvie ULg; Paydas, Hakan ULg et al

Conference (2013, September 12)

Additive manufacturing processes such as Selective Laser Melting (SLM) appear very promising in view of the economic production of near-net-shape, complex and (almost) fully dense parts from metallic ... [more ▼]

Additive manufacturing processes such as Selective Laser Melting (SLM) appear very promising in view of the economic production of near-net-shape, complex and (almost) fully dense parts from metallic materials such as Ti alloys and stainless steels. Practically, in SLM, a metallic powder is deposited layer-by-layer in a powder bed and then molten locally according to the desired shape. An important feature of this process is that the structure undergoes an ultra-fast cooling once the beam leaves the working zone, thus giving rise to strongly out-of-equilibrium microstructures. In the case of Ti alloy Ti-6Al-4V, in particular, the microstructural anisotropy resulting from the epitaxial growth of the newly deposited layer on the material previously solidified has been shown to exert a very strong influence on the mechanical properties [1]. In the present work, the microstructures and mechanical properties of Ti-6Al-4V and of stainless steel 316L processed by SLM have been characterised in details. Since these two materials exhibit quite different physical behaviours, their careful comparison might shed more light into the role of phenomena such as epitaxial growth, out-of-equilibrium phase transformation and/or internal stresses in determining the mechanical properties of metallic parts processed by SLM. [less ▲]

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See detailOn the Role of the Deterministic and Circumferential Stresses in Throughflow Calculations
Simon, Jean-Francois; Léonard, Olivier ULg

in Proceedings of the ASME Turbo Expo 2008 (2008, June)

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See detailOn the Role of the Deterministic and Circumferential Stresses in Throughflow Calculations
Simon, Jean-Francois; Thomas, Jean-Philippe ULg; Léonard, Olivier ULg

in Journal of Turbomachinery (2009), 131(3),

This paper presents a throughflow analysis tool developed in the context of the average-passage flow model elaborated by Adamczyk. The Adamczyk's flow model describes the 3D time-averaged flow field ... [more ▼]

This paper presents a throughflow analysis tool developed in the context of the average-passage flow model elaborated by Adamczyk. The Adamczyk's flow model describes the 3D time-averaged flow field within a blade row passage. The set of equations that governs this flow field is obtained by performing a Reynolds averaging, a time averaging, and a passage-to-passage averaging on the Navier–Stokes equations. The throughflow level of approximation is obtained by performing an additional circumferential averaging on the 3D average-passage flow. The resulting set of equations is similar to the 2D axisymmetric Navier–Stokes equations, but additional terms resulting from the averages show up: blade forces, blade blockage factor, Reynolds stresses, deterministic stresses, passage-to-passage stresses, and circumferential stresses. This set of equations represents the ultimate throughflow model provided that all stresses and blade forces can be modeled. The relative importance of these additional terms is studied in the present contribution. The stresses and the blade forces are determined from 3D steady and unsteady databases (a low-speed compressor stage and a transonic turbine stage) and incorporated in a throughflow model based on the axisymmetric Navier–Stokes equations. A good agreement between the throughflow solution and the averaged 3D results is obtained. These results are also compared to those obtained with a more “classical” throughflow approach based on a Navier–Stokes formulation for the endwall losses, correlations for profile losses, and a simple radial mixing model assuming turbulent diffusion. [less ▲]

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See detailOn the Role of the Running Coupling Constant in a Quark Model Analysis of T-odd TMDs
Courtoy, Aurore ULg

in International Journal of Modern Physics Conference Series (2011), 04

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See detailOn the role of the ventromedial prefrontal cortex in self-processing: the valuation hypothesis
D'Argembeau, Arnaud ULg

in Frontiers in Human Neuroscience (2013), 7

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See detailOn the Seismic Modelling of Rotating B-type Pulsators in the Traditional Approximation
Aerts, C.; Dupret, Marc-Antoine ULg

in ASP Conference Proceeding, Vol. 462, 103 (2012, September 01)

The CoRoT and Kepler data revolutionised our view on stellar pulsation. For massive stars, the space data revealed the simultaneous presence of low-amplitude low-order modes and dominant high-order ... [more ▼]

The CoRoT and Kepler data revolutionised our view on stellar pulsation. For massive stars, the space data revealed the simultaneous presence of low-amplitude low-order modes and dominant high-order gravity modes in several B-type pulsators. The interpretation of such a rich set of detected oscillations requires new tools. We present computations of oscillations for B-type pulsators taking into account the effects of the Coriolis force in the so-called traditional approximation. We discuss the limitations of classical frequency matching to tune these stars seismically and show that the predictive power is limited in the case of high-order gravity mode pulsators, except if numerous modes of consecutive radial order can be identified. [less ▲]

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See detailOn the sensitivity of closure phases to faint companions in optical long baseline interferometry
Le Bouquin, Jean-Baptiste; Absil, Olivier ULg

in Astronomy and Astrophysics (2012), 541

We explore the sensitivity and completeness of long baseline interferometric observations for detecting unknown, faint companions around bright unresolved stars. We derive a linear expression for the ... [more ▼]

We explore the sensitivity and completeness of long baseline interferometric observations for detecting unknown, faint companions around bright unresolved stars. We derive a linear expression for the closure phase signature of a faint companion in the high contrast regime (<0.1), and provide a quantitative estimation of the detection efficiency for the currently offered four-telescope configurations at the Very Large Telescope Interferometer. The results are compared to the performances provided by linear and Y-shaped interferometric configurations in order to identify the ideal array. We find that all configurations have a similar efficiency in discovering companions wider than 10mas. Assuming a closure phase accuracy of 0.25deg, that is typical of state-of-the-art instruments, we predict a median dynamic range of up to six magnitudes when stacking observations obtained at five different hour angles. Surveying bright stars to search for faint companions can be considered as an ideal filler programme for modern interferometric facilities because that places few constraints on the choice of the interferometric configuration. [less ▲]

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See detailOn the separation of net ecosystem exchange into assimilation and ecosystem respiration: review and improved algorithm
Reichstein, Markus; Falge, Eva; Baldocchi, Dennis et al

in Global Change Biology (2005), 11(9), 1424-1439

This paper discusses the advantages and disadvantages of the different methods that separate net ecosystem exchange (NEE) into its major components, gross ecosystem carbon uptake (GEP) and ecosystem ... [more ▼]

This paper discusses the advantages and disadvantages of the different methods that separate net ecosystem exchange (NEE) into its major components, gross ecosystem carbon uptake (GEP) and ecosystem respiration (R-eco). In particular, we analyse the effect of the extrapolation of night-time values of ecosystem respiration into the daytime; this is usually done with a temperature response function that is derived from long-term data sets. For this analysis, we used 16 one-year-long data sets of carbon dioxide exchange measurements from European and US-American eddy covariance networks. These sites span from the boreal to Mediterranean climates, and include deciduous and evergreen forest, scrubland and crop ecosystems. We show that the temperature sensitivity of R-eco, derived from long-term (annual) data sets, does not reflect the short-term temperature sensitivity that is effective when extrapolating from night- to daytime. Specifically, in summer active ecosystems the long-term temperature sensitivity exceeds the short-term sensitivity. Thus, in those ecosystems, the application of a long-term temperature sensitivity to the extrapolation of respiration from night to day leads to a systematic overestimation of ecosystem respiration from half-hourly to annual time-scales, which can reach > 25% for an annual budget and which consequently affects estimates of GEP. Conversely, in summer passive (Mediterranean) ecosystems, the long-term temperature sensitivity is lower than the short-term temperature sensitivity resulting in underestimation of annual sums of respiration. We introduce a new generic algorithm that derives a short-term temperature sensitivity of R-eco from eddy covariance data that applies this to the extrapolation from night- to daytime, and that further performs a filling of data gaps that exploits both, the covariance between fluxes and meteorological drivers and the temporal structure of the fluxes. While this algorithm should give less biased estimates of GEP and R-eco, we discuss the remaining biases and recommend that eddy covariance measurements are still backed by ancillary flux measurements that can reduce the uncertainties inherent in the eddy covariance data. [less ▲]

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See detailOn the Sets of Real Numbers Recognized by Finite Automata in Multiple Bases
Boigelot, Bernard ULg; Brusten, Julien ULg; Bruyère, Véronique

in Lecture Notes in Computer Science (2008, July), 5126

This paper studies the expressive power of finite automata recognizing sets of real numbers encoded in positional notation. We consider Muller automata as well as the restricted class of weak ... [more ▼]

This paper studies the expressive power of finite automata recognizing sets of real numbers encoded in positional notation. We consider Muller automata as well as the restricted class of weak deterministic automata, used as symbolic set representations in actual applications. In previous work, it has been established that the sets of numbers that are recognizable by weak deterministic automata in two bases that do not share the same set of prime factors are exactly those that are definable in the first order additive theory of real and integer numbers (R, Z, +, <). This result extends Cobham's theorem, which characterizes the sets of integer numbers that are recognizable by finite automata in multiple bases. In this paper, we first generalize this result to multiplicatively independent bases, which brings it closer to the original statement of Cobham's theorem. Then, we study the sets of reals recognizable by Muller automata in two bases. We show with a counterexample that, in this setting, Cobham's theorem does not generalize to multiplicatively independent bases. Finally, we prove that the sets of reals that are recognizable by Muller automata in two bases that do not share the same set of prime factors are exactly those definable in (R, Z, +, <). These sets are thus also recognizable by weak deterministic automata. This result leads to a precise characterization of the sets of real numbers that are recognizable in multiple bases, and provides a theoretical justification to the use of weak automata as symbolic representations of sets. [less ▲]

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See detailOn the Sets of Real Numbers Recognized by Finite Automata in Multiple Bases
Boigelot, Bernard ULg; Brusten, Julien ULg; Bruyère, Véronique

in Logical Methods in Computer Science (2010), 6(1), 1-17

This article studies the expressive power of finite automata recognizing sets of real numbers encoded in positional notation. We consider Muller automata as well as the restricted class of weak ... [more ▼]

This article studies the expressive power of finite automata recognizing sets of real numbers encoded in positional notation. We consider Muller automata as well as the restricted class of weak deterministic automata, used as symbolic set representations in actual applications. In previous work, it has been established that the sets of numbers that are recognizable by weak deterministic automata in two bases that do not share the same set of prime factors are exactly those that are definable in the first order additive theory of real and integer numbers. This result extends Cobham's theorem, which characterizes the sets of integer numbers that are recognizable by finite automata in multiple bases. In this article, we first generalize this result to multiplicatively independent bases, which brings it closer to the original statement of Cobham's theorem. Then, we study the sets of reals recognizable by Muller automata in two bases. We show with a counterexample that, in this setting, Cobham's theorem does not generalize to multiplicatively independent bases. Finally, we prove that the sets of reals that are recognizable by Muller automata in two bases that do not share the same set of prime factors are exactly those definable in the first order additive theory of real and integer numbers. These sets are thus also recognizable by weak deterministic automata. This result leads to a precise characterization of the sets of real numbers that are recognizable in multiple bases, and provides a theoretical justification to the use of weak automata as symbolic representations of sets. [less ▲]

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See detailOn the sets of real vectors recognized by finite automata in multiple bases
Brusten, Julien ULg

Doctoral thesis (2011)

This thesis studies the properties of finite automata recognizing sets of real vectors encoded in positional notation using an integer base. We consider both general infinite-word automata, and the ... [more ▼]

This thesis studies the properties of finite automata recognizing sets of real vectors encoded in positional notation using an integer base. We consider both general infinite-word automata, and the restricted class of weak deterministic automata, used, in particular, as symbolic data structures for representing the sets of vectors definable in the first order additive theory of real and integer numbers. In previous work, it has been established that all sets definable in the additive theory of reals and integers can be handled by weak deterministic automata regardless of the chosen numeration base. In this thesis, we address the reciprocal property, proving that the sets of vectors that are simultaneously recognizable in all bases, by either weak deterministic or Muller automata, are those definable in the additive theory of reals and integers. Precisely, for weak deterministic automata, we establish that the sets of real vectors simultaneously recognizable in two multiplicatively independent bases are necessarily definable in the additive theory of reals and integers. For general automata, we show that the multiplicative independence is not sufficient, and we prove that, in this context, the sets of real vectors that are recognizable in two bases that do not share the same set of prime factors are exactly those definable in the additive theory of reals and integers. Those results lead to a precise characterization of the sets of real vectors that are recognizable in multiple bases, and provide a theoretical justification to the use of weak automata as symbolic representations of sets. As additional contribution, we also obtain valuable insight into the internal structure of automata recognizing sets of vectors definable in the additive theory of reals and integers. [less ▲]

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See detailOn the shape of the UVBY lightcurves of CP stars
Mathys, G.; Manfroid, Jean ULg

in Astronomy and Astrophysics. Supplement Series (1985), 60

The authors present the lightcurves in the Strömgren system of 56 CP stars. The observational data have been fitted by a sine wave and its first harmonic. The least-square parameters are tabulated and it ... [more ▼]

The authors present the lightcurves in the Strömgren system of 56 CP stars. The observational data have been fitted by a sine wave and its first harmonic. The least-square parameters are tabulated and it is shown that such a fit describes very well the CP variations in most cases, the only exceptions being due to observational uncertainties. [less ▲]

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See detailOn the solution of the aeroelastic galloping problem
Vio, Gareth Arthur; Dimitriadis, Grigorios ULg; Cooper, Jonathan Edward

in Proceedings of the 2004 International Conference on Noise and Vibration Engineering (2004, September)

A global stability analysis of the transverse galloping of a square section beam in a normal steady ow was performed. The analysis was applied to a mathematical model using experimentally measured ... [more ▼]

A global stability analysis of the transverse galloping of a square section beam in a normal steady ow was performed. The analysis was applied to a mathematical model using experimentally measured stationary aerodynamic forces. The system was modelled as an ordinary differential equation with small non-linearity in the velocity term. Three methods are used for the stability analysis: 1. a harmonic balance approach, 2. normal form theory, 3. cell mapping. The resulting stability predictions were compared with each other and with results obtained from numerical integration. It is shown that the hysteretic stability of the non-linear aeroelastic oscillator was captured by all the methods. Additionally, the methods had a varying degree of success in predicting the amplitude of limit cycle oscillations undergone by the aeroelastic oscillator. [less ▲]

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See detailOn the sources of work hardening in multiphase steels assisted by transformation-induced plasticity
Jacques, Pascal J.; Furnémont, Quentin; Mertens, Anne ULg et al

in Philosophical Magazine A (2001), 81(7), 1789-1812

The mechanisms effectively responsible for the enhancement of the work-hardening capabilities of multiphase steels assisted by transformation-induced plasticity are highlighted. Different microstructures ... [more ▼]

The mechanisms effectively responsible for the enhancement of the work-hardening capabilities of multiphase steels assisted by transformation-induced plasticity are highlighted. Different microstructures, some containing a proportion of retained austenite with various mechanical stabilities, are studied. The dislocation density generated within ferrite by the mechanically induced martensitic transformation of retained austenite is shown to scale with the incremental work-hardening exponent. The acoustic emission generated during tensile straining was also measured. The acoustic emission was revealed to result mainly from dislocation motion, especially from the motion of the additional dislocation density generated in intercritical ferrite by the strain-induced martensitic transformation. [less ▲]

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See detailOn the spatial variation of double-sloped decay in coupled-volume concert halls
Billon, Alexis ULg

Conference (2007, September)

In a system of coupled rooms, a double-sloped can be observed in the room containing the source when the coupled room is more reverberant. This decay is formed of a first quick energy decrease due to the ... [more ▼]

In a system of coupled rooms, a double-sloped can be observed in the room containing the source when the coupled room is more reverberant. This decay is formed of a first quick energy decrease due to the first room and a second slower one due to the energy which is fed back from the coupled room. Today, this effect is used to obtain simultaneously clarity and reverberance in concert halls. Parameters to achieve a strong double-sloped decay are now well known. In this preliminary work, the spatial variation of the double decay strength within the concert hall is studied using numerical simulations. Firstly, the indicators quantifying the double decay used in this study are presented. Then, the results of two configurations with the same coupling characteristics but with different coupling area locations are compared. Finally, an empirical model based on the statistical theory is proposed. [less ▲]

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See detailOn the specificity of cyclodextrin complexes detected by electrospray mass spectrometry
Gabelica, Valérie ULg; Galic, Nives; De Pauw, Edwin ULg

in Journal of the American Society for Mass Spectrometry (2002), 13(8), 946-953

alpha-cyclodextrin complexes with linear alpha,omega-dicarboxylic acids were investigated by electrospray mass spectrometry. These hydrophobic complexes are known to have an equilibrium binding constant ... [more ▼]

alpha-cyclodextrin complexes with linear alpha,omega-dicarboxylic acids were investigated by electrospray mass spectrometry. These hydrophobic complexes are known to have an equilibrium binding constant that increases with the diacid chain length. However, the electrospray mass spectrometry (ES-MS) spectra showed that the relative intensity of the complex did not vary significantly with chain length. This contradiction is caused by a contribution of nonspecific adducts to the signal of the complex in ES-MS. In order to estimate the contribution of nonspecific adducts to the total intensity of the complexes with alpha-cyclodextrin, the comparison was made between alpha-cyclodextrin and maltohexaose, the latter being incapable of making inclusion complexes in solution. The signal observed for complexes between diacids and maltohexaose can only result from nonspecific electrostatic aggregation, and is found to be more favorable with the shorter diacids. This is also supported by MS/MS experiments. A procedure is described which allows estimation of the contribution of the nonspecific complex in the spectra of the complexes with alpha-cyclodextrin by using the relative intensity of the complex with maltohexaose. The contribution of the specific complex to the total signal intensity is found to increase with the diacid chain length, which is in agreement with solution behavior. [less ▲]

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See detailOn the spectral bands measurements for combustion monitoring
Arias, Luis; Torres, S; Sbarbaro, D et al

in Combustion and Flame (2011), 158

In this work, spatial–spectral experimental issues affecting the detection of radical emissions in a natural gas flame are discussed and studied by a radiometric analysis of the flame spectral emission ... [more ▼]

In this work, spatial–spectral experimental issues affecting the detection of radical emissions in a natural gas flame are discussed and studied by a radiometric analysis of the flame spectral emission. As results of this analysis, Local and Global Spectral Radiation Measurements (LSRM and GSRM respectively) techniques are proposed, and guidelines for selecting the radical emission bands and spatial location of photodetectors are given. Two types of experiments have been performed in order to demonstrate the reliability of the GSRM technique for combustion characterization. In the first experiment, the LSRM and the GSRM have been implemented by using a home made sensor array, based on silicon photodiodes, for sensing the excited CH* and C2 radicals in a natural gas flame. It has been experimentally that by using the GSRM, the signal’s dispersion can be reduced to about 86% for the CH* and 76% for the C2 with respect to the obtained values with LSRM methodology. In the second experiment, the GSRM technique has been applied for sensing the CH* and C2 radicals, where it has been found that the signals emissions ratio C2/CH* provides a good indicator of the thermal combustion efficiency and the CO pollutants emissions, with small dispersion. Thus, the GSRM technique has corroborated the usefulness of that ratio for combustion monitoring. [less ▲]

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See detailOn the spectrum of H II regions
Manfroid, Jean ULg

in Bulletin de l'Academie Royale de Belgique (1979), 65

It is demonstrated that the validity of present models of H II regions is not well established. It is clear that simple models (and the usual formulas involving line ratios) are unable to provide a ... [more ▼]

It is demonstrated that the validity of present models of H II regions is not well established. It is clear that simple models (and the usual formulas involving line ratios) are unable to provide a correct interpretation of the nebular spectrum. The importance of several geometrical and density effects which may account for some peculiar spectral features (such as bright forbidden S II lines and anomalous abundances) is emphasized. It is concluded that the best course to follow in H II region spectral analysis is the comparison of observations and sophisticated models on a statistical basis. [less ▲]

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See detailOn the spectrum of recombining H II regions
Manfroid, Jean ULg

in Astronomy and Astrophysics (1976), 51

The spectrum of collisionally excited lines in fossil H II regions of various densities is computed. The emission by ions of eight heavy elements is taken into account.

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