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See detailFrequency halving due to vortex pairing for the jet-slot oscillator
Billon, Alexis ULg; Glesser, Martin; Valeau, Vincent et al

Conference (2006, July)

At the outlet of the HVCA systems, whistling can occur, due to self-sustained oscillations. In this study, the ventilation outlet is modelled by a free plane subsonic jet impinging on a slotted plate ... [more ▼]

At the outlet of the HVCA systems, whistling can occur, due to self-sustained oscillations. In this study, the ventilation outlet is modelled by a free plane subsonic jet impinging on a slotted plate, leading to self-sustained tones production; this configuration is known as the jet-slot oscillator. The tone's frequency can be predicted through the vortex dynamics within the flow. For jet velocities higher than 16m/s, the tones couple with the flow-supply-duct’s resonances. These resonances control the vortex dynamics and reinforce the sound production, of about 20dB. Moreover, when the distance from the jet exit to the plate is increased and reaches 4.5 times the jet height, the fundamental frequency of the tones is suddenly halved due to some vortex pairing occurring at the end of the potential core of the jet. In this paper, the vortex pairing is observed with three different experimental techniques. Firstly, comparison between the radiated and the in-duct acoustic fields is conducted. Then the energy transfer from the fundamental to the sub-harmonics of the shear layer's velocity fluctuations is observed with anemometric measurements. Finally high speed flow visualizations are performed and allow to link the vortex impingement on the plate to the sound production. [less ▲]

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See detailThe frequency of Ap-stars with long rotation periods
Hensberge, H.; Manfroid, Jean ULg; Renson, Pierre ULg et al

in Astronomy and Astrophysics (1984), 132

Light variability was observed over time intervals of months to years in the stars HD 55540, HD 71066, HD 94660, and HD 187474. The significance of these results is discussed in terms of the frequency of ... [more ▼]

Light variability was observed over time intervals of months to years in the stars HD 55540, HD 71066, HD 94660, and HD 187474. The significance of these results is discussed in terms of the frequency of chemically peculiar CP2 stars showing (light) variability with periods longer than one month. This frequency, relative to the whole CP2 population, must lie somewhere between 4 and 16 percent. Observations, properly distributed in time, of a small subgroup of CP2 stars will be sufficient to obtain an accurate ratio of the number of LP-CP2 stars to the total number of CP2 stars. These observations, when continued until the periodicity is detected, could contribute also to the discussion whether these long periods should be identified with the rotation period. [less ▲]

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See detailThe frequency of cutaneous vasculitis is not increased in patients with rheumatoid arthritis treated with methotrexate
Kaye, O.; Beckers, C. C.; Paquet, P. et al

in Journal of Rheumatology (1996), 23(2), 253-257

OBJECTIVE: To analyse the frequency, type, and immunohistological features of clinical cutaneous vasculitis developing in patients with rheumatoid arthritis (RA) treated or not with methotrexate as well ... [more ▼]

OBJECTIVE: To analyse the frequency, type, and immunohistological features of clinical cutaneous vasculitis developing in patients with rheumatoid arthritis (RA) treated or not with methotrexate as well as their demographic, clinical and biological characteristics. METHODS: Ninety-one patients with RA receiving 9.5 mg/wk of methotrexate (MTX) were compared for an average observation time of 18 months to 130 matched patients with RA treated with various drugs excluding MTX. RESULTS: Whether receiving MTX or not, 5.4% of patients with RA developed a clinical cutaneous vasculitis. There were significant differences between both groups for 2 variables only: a higher percentage of polyneuropathies and a higher level of immune complex-plasma levels in non-MTX patients. The immunohistological analysis did not differentiate both groups. CONCLUSION: The percentage of cutaneous vasculitis that developed under MTX therapy was not different from that occurring as a natural complication of longstanding severe RA. [less ▲]

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See detailThe Frequency of Plasmodesmata Increases Early in the Whole Shoot Apical Meristem of Sinapis Alba L. During Floral Transition
Ormenese, Sandra ULg; Havelange, Andrée ULg; Deltour, Roger ULg et al

in Planta (2000), 211(3), 370-5

The frequency of plasmodesmata increases in the shoot apical meristem of plants of Sinapis alba L. induced to flower by exposure to a single long day. This increase is observed within all cell layers (L1 ... [more ▼]

The frequency of plasmodesmata increases in the shoot apical meristem of plants of Sinapis alba L. induced to flower by exposure to a single long day. This increase is observed within all cell layers (L1, L2, L3) as well as at the interfaces between these layers, and it occurs in both the central and peripheral zones of the shoot apical meristem. The extra plasmodesmata are formed only transiently, from 28 to 48 h after the start of the long day, and acropetally since they are detectable in L3 4 h before they are seen in L1 and L2. These observations indicate that (i) in the Sinapis shoot apical meristem at floral transition, there is an unfolding of a single field with increased plasmodesmatal connectivity, and (ii) this event is an early effect of the arrival at this meristem of the floral stimulus of leaf origin. Since (i) the wave of increased frequency of plasmodesmata is 12 h later than the wave of increased mitotic frequency (A. Jacqmard et al. 1998, Plant cell proliferation and its regulation in growth and development, pp. 67 78; Wiley), and (ii) the increase in frequency of plasmodesmata is observed in all cell walls, including in walls not deriving from recent divisions (periclinal walls separating the cell layers), it is concluded that the extra plasmodesmata seen at floral transition do not arise in the forming cell plate during mitosis and are thus of secondary origin. [less ▲]

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See detailFrequency of Solar-like Systems and of Ice and Gas Giants Beyond the Snow Line from High-magnification Microlensing Events in 2005-2008
Gould, A.; Dong, Subo; Gaudi, B. S. et al

in Astrophysical Journal (2010), 720

We present the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval –4.5 < log q < –2, corresponding to the range of ice giants to gas giants. We ... [more ▼]

We present the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval –4.5 < log q < –2, corresponding to the range of ice giants to gas giants. We find \endgraf\vbox{\begin{center}$\displaystyle{d^2 N{_{\rm pl}}\over d\log q\, d\log s} = (0.36\pm 0.15)\;{\rm dex}^{-2}$\end{center}}\noindentat the mean mass ratio q = 5 × 10 –4 with no discernible deviation from a flat (Öpik's law) distribution in log-projected separation s. The determination is based on a sample of six planets detected from intensive follow-up observations of high-magnification ( A>200) microlensing events during 2005-2008. The sampled host stars have a typical mass M host ~ 0.5 M sun [less ▲]

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See detailFrequency of Solar-Like Systems and Planet Mass-Ratio Distribution Function Beyond the Snow Line from High-Magnification Microlensing Events
Gould, A.; Dong, S.; Gaudi, B~S et al

in Astrophysical Journal (2010), 720

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See detailThe frequency ratio method and the new multiperiodic gamma Doradus star HD 218427
Rodríguez, E.; Amado, P. J.; Suárez, J. C. et al

in Astronomy and Astrophysics (2006), 450

Oscillations of gamma Dor-type were discovered in the star HD 218427 through simultaneous uvby photometric observations carried out in the year 2003. A few Hbeta-Crawford measurements were also collected ... [more ▼]

Oscillations of gamma Dor-type were discovered in the star HD 218427 through simultaneous uvby photometric observations carried out in the year 2003. A few Hbeta-Crawford measurements were also collected for calibration purposes and they locate this star well inside the gamma Dor instability region. We find HD 218427 to be deficient in metals, similar to other well-defined gamma Dor stars, and discuss the possibility that it has a lambda Boo nature. We carried out frequency analysis for different filters, including the combined "vby" filter, and five frequencies were found as significant with periods ranging between 0.3 and 0.8 days. The recently-developed frequency ratio method is used in order to identify the excited modes. The results are consistent with an l=2 identification for all the modes and with high radial quantum numbers (nË 40) for the three main observed periodicities. The possibility of multiplet structures is also discussed. However, no consistency is found when using the time-dependent convection treatment to discriminate modes. This disagreement can be due to the large rotation velocity taking place in HD 218427 and, consequently, the significant coupling between the modes. [less ▲]

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See detailFrequency, characteristics, and functions of future-oriented thoughts in daily life
D'Argembeau, Arnaud ULg; Renaud, Olivier; Van der Linden, Martial ULg

in Applied Cognitive Psychology (2011), 25

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See detailA Frequency-domain Approach to Subspace Identification of Nonlinear Systems, Application to Aerospace Structures
Noël, Jean-Philippe ULg

Doctoral thesis (2014)

The construction of mathematical models from experimental data is an essential step in the design process of engineering systems. The different tasks involved in this activity, from the measurement and ... [more ▼]

The construction of mathematical models from experimental data is an essential step in the design process of engineering systems. The different tasks involved in this activity, from the measurement and processing of data to the validation of the model, fall into the general field of system identification. In structural dynamics, the theoretical and experimental aspects of linear system identification have been successfully addressed since the early seventies, and mature analytical, computational and testing tools have emerged. Nonlinear system identification of vibrating structures has also enjoyed significant advances during the past few years. However, the common practice in industry is to ignore nonlinearities, arguably because their analysis is still regarded as impractical. The objective of this doctoral thesis is precisely to progress towards the development of a practical system identification methodology dedicated to real-life nonlinear structures. The first facet of the thesis is to introduce a nonlinear generalisation in the frequency domain of the so-called subspace identification methods. The proposed frequency-domain nonlinear subspace identification (FNSI) approach yields accurate models of large-scale systems comprising strong nonlinearities, closely-spaced modes and high damping. Because it can also estimate a large number of parameters while maintaining an acceptable computational burden, the second facet of this research is to investigate the utilisation of cubic splines as a very flexible means to model complex nonlinearities. Finally, the third facet of the present work is to derive nonlinear models with optimal statistical properties in the presence of measurement noise. This is achieved by embedding the FNSI method into the maximum likelihood identification framework. The scope of the identification and modelling tools developed in this thesis encompasses nonlinear structural systems originating from the various areas of vibration engineering, including the aerospace, mechanical or civil fields, amongst others. Throughout the dissertation, these tools are illustrated using numerical and experimental structures of increasing complexity, mainly related to aerospace applications. [less ▲]

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See detailA Frequency-Domain Processor for Maximum Resolution and Quicklook Processing of Wide-Swath ASAR Images
Barbier, Christian ULg; Piette, François; Renson, Luc et al

in Proc. EUSAR'96 Conference (1996)

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See detailA Frequency-Domain Processor for ScanSAR Images
Barbier, Christian ULg; Rosello-Guasch, Josep

in Preparing for the Future (1995), 5(4), 6-7

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See detailFrequency-domain subspace identification for nonlinear mechanical systems
Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg

in Mechanical Systems & Signal Processing (2013), 40

This paper introduces a new frequency-domain subspace-based method for the identification of nonlinear mechanical systems. The technique exploits frequency-domain data and interprets nonlinearities as ... [more ▼]

This paper introduces a new frequency-domain subspace-based method for the identification of nonlinear mechanical systems. The technique exploits frequency-domain data and interprets nonlinearities as feedback forces exciting the underlying linear system. It is first demonstrated using two academic examples, namely a Duffing oscillator and a five-degree-of-freedom system comprising two nonlinearities. The identification of an experimental beam exhibiting geometrically nonlinear behaviour is then addressed. [less ▲]

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See detailFrequency-domain subspace identification of nonlinear mechanical systems
Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg

in Proceedings of the 5th International Operational Modal Analysis Conference (2013, May)

The objective of the present paper is to address the identification of a real-life strongly nonlinear space structure, the EADS-Astrium SmallSat spacecraft. To this end, a new nonlinear subspace ... [more ▼]

The objective of the present paper is to address the identification of a real-life strongly nonlinear space structure, the EADS-Astrium SmallSat spacecraft. To this end, a new nonlinear subspace identification method formulated in the frequency domain is exploited, referred to as the FNSI method. The frequency response functions of the underlying linear spacecraft and the amplitudes of the nonlinear internal forces are estimated based on a periodic-random data set corrupted by noise. This application is challenging for several reasons, including high modal density, highly non-proportional damping and the non-smooth nature of the nonlinearities. [less ▲]

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See detailFrequency-domain subspace identification of nonlinear mechanical systems - Application to a solar array structure
Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg; Foltête, Emmanuel et al

in Proceedings of the International Modal Analysis Conference (IMAC) XXXI (2013, February)

The present paper addresses the experimental identification of a simplified realisation of a solar array structure in folded configuration. To this end, a nonlinear subspace identification technique ... [more ▼]

The present paper addresses the experimental identification of a simplified realisation of a solar array structure in folded configuration. To this end, a nonlinear subspace identification technique formulated in the frequency domain, referred to as the FNSI method, is exploited. The frequency response functions of the underlying linear structure and the nonlinear coefficients are estimated by this approach. Nonlinearity is caused by impacts between adjacent panels and friction and gaps appearing in their clamping interfaces. This application is challenging for several reasons, which include high modal density and the complicated nature of the involved nonlinear mechanisms. [less ▲]

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See detailLa fréquentation des massifs forestiers à des fins récréatives et de détente pour la population wallonne et bruxelloise
Colson, Vincent ULg

in Forêt Wallonne (2006), (81), 26-38

Une enquête téléphonique menée auprès de 1 005 personnes habitant les régions bruxelloise et wallonne a tenté de caractériser le type de public qui se rend en forêt, les périodes recherchées ou encore les ... [more ▼]

Une enquête téléphonique menée auprès de 1 005 personnes habitant les régions bruxelloise et wallonne a tenté de caractériser le type de public qui se rend en forêt, les périodes recherchées ou encore les activités pratiquées. Les destinations choisies et le consentement à payer pour ce type de loisir ont également été abordés. [less ▲]

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See detailLa fréquentation des massifs forestiers wallons: le public, ses activités et sa perception de la forêt
Colson, Vincent ULg

in Forêt Wallonne (2007), (87), 20-35

Une enquête a été menée entre octobre 2005 et août 2006 au sein de quarante massifs forestiers afin de pouvoir dresser l’image la plus fidèle de la fréquentation de la forêt wallonne. Les questions posées ... [more ▼]

Une enquête a été menée entre octobre 2005 et août 2006 au sein de quarante massifs forestiers afin de pouvoir dresser l’image la plus fidèle de la fréquentation de la forêt wallonne. Les questions posées ont permis de caractériser le profil du public, les activités pratiquées et la façon dont est perçue la forêt. [less ▲]

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See detailLa fréquentation des promenades balisées en forêt wallonne. Résultat d'une enquête menée avec la collaboration de huit organismes touristiques wallons
Colson, Vincent ULg

in Les Echos du Tourisme (2006), (44), 7-8

Dans le cadre d’une étude portant sur l’évaluation de la fonction récréative de la forêt wallonne, une enquête a été réalisée entre le 1er mai et le 7 novembre 2005 auprès des utilisateurs de cartes de ... [more ▼]

Dans le cadre d’une étude portant sur l’évaluation de la fonction récréative de la forêt wallonne, une enquête a été réalisée entre le 1er mai et le 7 novembre 2005 auprès des utilisateurs de cartes de promenades de 8 organismes touristiques (Florenville, Spa, Saint-Hubert, Nassogne, Assesse, Viroinval, Lobbes et Villersla- Ville). Les personnes acquérant une carte de promenades étaient invitées à répondre à un questionnaire à renvoyer au moyen d’une enveloppe « port payé par le destinataire ». Malgré un faible taux de réponse (196 soit 6,3%), des informations intéressantes ont pu être obtenues sur le profil des promeneurs et sur leurs desiderata. Cet article reprend quelques-uns des principaux résultats obtenus. [less ▲]

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See detailFrequently Relapsing Crohn's Disease Is Characterized by Persistent Elevation in Interleukin-6 and Soluble Interleukin-2 Receptor Serum Levels During Remission
Van Kemseke, Catherine ULg; Belaiche, Jacques ULg; Louis, Edouard ULg

in International Journal of Colorectal Disease (2000), 15(4), 206-10

We examined immune and inflammatory activation during remission in patients with Crohn's disease who presented with various clinical profiles (prolonged remission vs. relapsing disease). Thirty-six ... [more ▼]

We examined immune and inflammatory activation during remission in patients with Crohn's disease who presented with various clinical profiles (prolonged remission vs. relapsing disease). Thirty-six patients with at least 3 years' follow-up starting from a remission period were studied retrospectively. Relapses were defined by a retrospective calculation of the Crohn's disease activity index or by the clinical judgement of the physicians in charge of the patients. Disease course over the study period was assessed by the mean number of annual relapses. Analysis used measurements during remission of the following: erythrocytes sedimentation rate, relative lymphocytosis, acid alpha1-glycoprotein, interleukin-6 (IL-6), and soluble interleukin-2 receptor (sIL-2R) serum levels. During the study period 21 patients experienced at least one relapse and 15 did not. Mean serum levels of sIL-2R and mean relative lymphocytosis in remission significantly discriminated between relapsing and nonrelapsing patients. Only the mean sIL-2R serum level was selected by multivariate analysis, with a cutoff value of 82 pM/1 (sensitivity of 76% and specificity of 80%). The only features correlated with mean number of annual relapses in the relapsing patients were mean serum levels of sIL-2R (r=0.58, P=0.015) and IL-6 in remission (r=0.45, P=0.039). Multivariate analysis demonstrated statistical significance only for the mean serum level of IL-6 (P=0.014). In Crohn's disease the persistent elevation in sIL-2R serum levels during remission corresponds to chronic active disease, while high serum levels of IL-6 in these patients is associated with a high frequency of relapse. [less ▲]

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See detailFrères et soeurs pour la vie? : Les relations fraternelles à l'épreuve du temps
Favart, Evelyne ULg

Book published by Cortext (2007)

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