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See detailLouis Althusser. Politique et subjectivité. Editorial
Bruschi, Fabio; Mancuso, Eva ULg

in Cahiers du GRM (2015), VII

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See detailNonlinear ground vibration identification of an F-16 aircraft - Part 2: Parameter estimation using a frequency-domain subspace method
Dossogne, Tilàn ULg; Noël, Jean-Philippe ULg; Kerschen, Gaëtan ULg et al

in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics (2015, June)

Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic ... [more ▼]

Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic nonlinearity, is the modelling of the wing-to-payload mounting interfaces. For large amplitudes of vibration, friction and gaps may be triggered in these connections and markedly impact the dynamic behaviour of the complete structure. In this series of two papers, the nonlinear dynamics of an F-16 aircraft is investigated using rigorous methods applied to real data collected during a ground vibration test campaign. The present work focuses on the construction of an experimental mathematical model of the F-16 structural dynamics. A nonlinear generalisation in the frequency domain of the so-called subspace identification algorithms, termed FNSI method, is exploited to this end. The frequency response functions of the underlying linear aircraft and the coefficients of the nonlinearities are reliably estimated by this approach based on periodic random data. The use of stabilisation diagram in nonlinear system identification is also discussed. The application of the FNSI method is made challenging by the high modal density of the structure, and the complexity of the nonlinear stiffness and damping mechanisms involved within the wing-to-payload connections. [less ▲]

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See detailA frequency-domain method for identifying nonlinear vibrating structures
Noël, Jean-Philippe ULg; Dossogne, Tilàn ULg; Kerschen, Gaëtan ULg

Conference (2015, June)

System identification, which refers to the construction of mathematical models from experimental data, plays a key role in the design process of engineering systems. In structural dynamics, the ... [more ▼]

System identification, which refers to the construction of mathematical models from experimental data, plays a key role in the design process of engineering systems. 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 present work describes a rigorous nonlinear generalisation in the frequency domain of the classical subspace identification algorithms, termed FNSI method. This method is applicable to large-scale systems comprising strong nonlinearities, closely-spaced modes and potentially high, nonproportional damping. Another distinct advantage of the approach is that it offers a convenient way to select an appropriate order for the nonlinear model by means of stabilisation diagrams. The FNSI method is demonstrated in this study using a complete satellite structure with nonsmooth nonlinearities, and a solar panel assembly exhibiting complex nonlinear stiffness and damping mechanisms. [less ▲]

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See detailNonlinear ground vibration identification of an F-16 aircraft - Part 1: Fast nonparametric analysis of distortions in FRF measurements
Vaes, Mark; Schoukens, Johan; Peeters, Bart et al

in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics (2015, June)

Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic ... [more ▼]

Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic nonlinearity, is the modelling of the wing-to-payload mounting interfaces. For large amplitudes of vibration, friction and gaps may be triggered in these connections and markedly impact the dynamic behaviour of the complete structure. In this series of two papers, the nonlinear dynamics of an F-16 aircraft is investigated using rigorous methods applied to real data collected during a ground vibration test campaign. The present work focuses on the detection, qualification and quantification of nonlinear distortions affecting frequency response function (FRF) measurements. The key idea of the approach is to excite the structure using a random signal with a user-defined amplitude spectrum, where only a set of well-selected frequencies is different from zero in the band of interest. It is demonstrated that this careful choice of the input frequencies allows, without any further user interaction, to quantify the importance of odd and even nonlinear distortions in the output spectra with respect to the noise level. At high excitation amplitude, the F-16 dynamics is found to exhibit substantial odd nonlinearities and less significant, yet not negligible, even nonlinearities. [less ▲]

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See detailNonlinear model updating by means of identified nonlinear normal modes
Song, Mingming; Renson, Ludovic ULg; Noël, Jean-Philippe ULg et al

Conference (2015, June)

Modal parameters are the most common features used for linear model updating. Although the modal analysis theory does not hold for nonlinear dynamic systems, its popularity encouraged researchers to come ... [more ▼]

Modal parameters are the most common features used for linear model updating. Although the modal analysis theory does not hold for nonlinear dynamic systems, its popularity encouraged researchers to come up with an equivalent version of normal modes for nonlinear systems, i.e., nonlinear normal modes (NNMs). A nonlinear system vibrates in NNMs when all masses have periodic motions of the same period, and at any time, the position of all the masses is uniquely defined by the position of any one of them. This paper investigates the feasibility of nonlinear model updating by minimizing the difference between the model-predicted and measured/identified nonlinear normal modes. A two degree-of-freedom mass-spring system with three linear springs and a cubic nonlinear spring is considered as the case study. The energy-dependent natural frequency and NNM of the first vibration mode of the system are identified at three different levels of energy. The stiffness parameters of the system are estimated by minimizing an objective function which is defined as the discrepancy between model-predicted natural frequency and NNM of the first mode, and their identified counterparts at the three measured energy levels. Performance of the proposed updating approach is evaluated at different levels of noise and different levels of modeling errors (i.e., nonlinear model classes). [less ▲]

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See detailAuroral Morphologies of Jupiter and Saturn
Grodent, Denis ULg

Conference (2015, May 31)

We review the principal differences and similarities of the morphologies of Jupiter and Saturn's auroral emissions. We then show some examples of UV images that are expected to be acquired with Cassini ... [more ▼]

We review the principal differences and similarities of the morphologies of Jupiter and Saturn's auroral emissions. We then show some examples of UV images that are expected to be acquired with Cassini UVIS at Saturn and Juno UVS at Jupiter. [less ▲]

Detailed reference viewed: 12 (1 ULg)
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See detailComparing central western Europe Mesolithic and Neolithic plant processing microwear on flint tool
Linton, Jimmy ULg; Guéret, Colas; Gassin, Bernard

Conference (2015, May 30)

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See detailTowards an experiment based protocol for extracting and identifying residues
Cnuts, Dries ULg; Rots, Veerle ULg

Conference (2015, May 29)

Residue analysis has recently become a widely applied method in reconstructing the lifecycle of prehistoric stone tools. The identification of residues is traditionally based on the distinctive ... [more ▼]

Residue analysis has recently become a widely applied method in reconstructing the lifecycle of prehistoric stone tools. The identification of residues is traditionally based on the distinctive morphologies of the residue fragments by means of light microscopy. The majority of residue fragments, however, tend to have an amorphous structure and are therefore not easy to identify. In addition, some residue categories can only be detected by using transmitted light microscopy, which requires the extraction of residues from the tool’s surface. Yet another challenge is to determine whether the residues were deposited on the tool’s surface as a result of use or due to other processes. Here we present the results of an experimental study that addresses these methodological issues. Stone tools from a new experimental reference collection were used to test 6 different analytical methods: the observation of residues on stone tools with incident light microscopy, dry sampling using tweezers and brushes, wet sampling with micropipettes using distilled water and a tri-mixture of acetonitrile, ethanol and water, and extraction with an ultrasonic scaler or bath. The experiments demonstrate that the choice of a particular extraction procedure may influence the amount and types of residues that are extracted. This implies that the analytical method has an impact on the results of a residue analysis. Building on these data, we designed a new protocol, which was subsequently submitted to blind testing in order to test its accuracy and precision. Certain key attributes were also identified that may prove useful in distinguishing between use-related and natural residues. We discuss the importance of adapting analytical protocols to the research question of the study. [less ▲]

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See detailToward a more precise terminology for impact damage and an improved understanding of hunting weapons: First results from a large scale systematic experiment
Coppe, Justin ULg; Rots, Veerle ULg

Conference (2015, May 29)

Projectile points have recently taken an important place in debates on the complexity of Palaeolithic human behaviour. While the appearance of hunting weapons in the archaeological record was an important ... [more ▼]

Projectile points have recently taken an important place in debates on the complexity of Palaeolithic human behaviour. While the appearance of hunting weapons in the archaeological record was an important element in the past, current discussions focus a lot on the appearance of particular hunting methods. Distinctions are made between simple and complex weaponry, the latter assumed to be linked with modern humans only. While most of the identifications of hunting weapons in the archaeological record rely on the examination of so-called diagnostic impact damage, no reliable reference yet exist for distinguishing between hunting methods. We present the first results of a large-scale and systematic experiment that intends to address hunting weapons in a systematic way. A thorough survey of the literature has highlighted some existing ambiguity in current terminological frameworks for describing impact fractures. Based on our experiments, we propose some attributes that may be relevant for improving these terminologies. Attention will also be devoted to the design and conceptual framework of our experimental program and to some first results concerning the essential variables influencing damage formation. The overall goal is to improve our understanding of the different fracture phenomena and their variability in order to enhance the reliability of the identification of hunting weapons and perhaps of their projecting mode. [less ▲]

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See detailQuelles caractéristiques du passage à la retraite ont un impact sur la cognition du sujet âgé ? Résultats de la cohorte AMI
Grotz, Catherine ULg; Matharan, Fanny; Amieva, Hélène et al

Conference (2015, May 29)

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See detailTable-ronde autour de l'ouvrage : M. Hagelstein, "Origine et survivances des symboles. Warburg, Cassirer, Panofsky"
Hagelstein, Maud ULg

Scientific conference (2015, May 29)

Table-ronde - échange questions/réponses - avec la participation de : Muriel VAN VLIET, Raphaël GÉLY, Rudy STEINMETZ, Alievtina HERVY, Bruno LECLERCQ

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See detailTime and aspect: what the academic grammars say, and what the texts actually show
Winand, Jean ULg

Scientific conference (2015, May 29)

Detailed reference viewed: 31 (1 ULg)
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See detailFragmentation urbaine à travers les réseaux techniques
Cabrera Quispe, Juan Edson ULg

Doctoral thesis (2015)

Since about three decades ago, the networking services (water, energy, transport and telecommunications) are the subject of studies and mainly reforms (liberalization, privatization and concessions to ... [more ▼]

Since about three decades ago, the networking services (water, energy, transport and telecommunications) are the subject of studies and mainly reforms (liberalization, privatization and concessions to private companies, etc.) and also an important economic policy issue. However the possible effects of these reforms on the fragmentation or integration of urban societies are still poorly studied, although some studies (mainly on developing cities) support the thesis that there would be a growing urban fragmentation, reinforced by the dominant modes of implementing reforms network services. One of the most important theses about the subject is in a relatively recent development of the English authors Stephen Graham and Simon Marvin (2001). Their work generalizes the motion of fragmentation (splintering Urbanism) to all network services and a set of economic regions in the world. While this thesis presents consistency and validity - since it is known that the application of models of decentralization and liberalization of services has an effect on the fragmentation - the position of fragmentation due to centralized networks is inside a new analysis framework and still incomplete considering the absence of more empirical evidence. The thesis of fragmentation from centralized networks suggests that powerful factors are contributing to the disintegration of infrastructure, favoring the fragmentation of the social structure and material of cities. In fact, this breakdown of infrastructures makes possible many strategies of evasion; they are addressed to connect powerful users and valorized spaces, preventing the connection with less powerful users and poor spaces. These processes lead to the creation of spaces from different social networks, resulting in social elites living every day in places disconnected from the urban structure of the set (in gated communities, new complex people and other planned communities), as well as the lower classes, but the latter with the worst conditions. The main hypothesis of the "splintering Urbanism" argues that network services have an integrated character and are precisely the privatization and liberalization of services that contribute to the breakdown of network infrastructure and urban fragmentation feed. The control of networks from powerful coalitions of actors, separation and segmentation boost infrastructure in different network elements and service pack (2001: 141). This separation would occur across strategies "bypass" or "wrap" seeking to connect users, valuable or powerful places, and through discarding or dodge weaker users and worthless places. Our thesis "Urban Fragmentation through technical networks," confirms and reinforces the thesis made by Graham & Marvin, across expounding on the Cochabamba Bolivian context, a set of technical networks of small-scale or micro decentralized networks which are managed by autonomous social organizations that also fragment the territory without the need for "by pass" and the socio-spatial differentiation, but through the realization of strategies linked to autonomous administration and management of common and basic goods like water. This thesis demonstrates the existence of processes of spatial dislocation and loss of solidarity (main evils of urban fragmentation) across the dynamics of technical devices and decentralized networks infrastructure services from private-community water and small scale. However, our work describes in its urban development, territorial and environmental problems inside the phenomenon. The paper first presents a set of theories that attempt to explain the fragmentation and its particularities, then describes the socio-spatial formation of the study area whose characteristics allow this type of phenomenon, to arrive to a section that exposes all the particularities of the management water from public and local actors, analyzed from the environmental logic of urban water cycle, including the specifics of the main stage of study of this thesis, the municipality of Quillacollo in Cochabamba. From a spatial perspective, the thesis exhibits the characteristics of urban fragmentation across technical networks, exposing the details related to the organization of urban space as a result of processes of spatial dislocation, loss of solidarity and exercise of territoriality in small networks. It is concluded in a discussion about the validity of the strategies in terms of access to the resource, the possibilities of intervention and reflections about the power relationships among fragments and for water control. Finally, as a supplement, urban fragmentation through small technical networks, also allows to display the tensions between two ways of managing the territory (centralized view from the public sector and decentralized vision from local communities) highlighting the uncomfortable and marginalized urban planning position, but challenging the urbanism to recover to action on the highly fragmented contemporary cities with complex scenarios of governance and sometimes rare or endangered resources. [less ▲]

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See detailAntitrust and The challenge of policing « moligopolists »
Petit, Nicolas ULg

Conference (2015, May 29)

Detailed reference viewed: 12 (1 ULg)