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See detailDynamic Thermal Modeling of a Radiant Panel System and its Environment for Commissioning: Application to a Case Study
Fonseca Diaz, Nestor; Bertagnolio, Stéphane ULg

in Proceedings of the 9th International Conference for Enhanced Building Operation, Austin, TX (2009, November)

As a part of a commissioning study, the cooling ceiling system of a large commercial building located in Belgium is evaluated. A representative office has been instrumented and data on the cooling ceiling ... [more ▼]

As a part of a commissioning study, the cooling ceiling system of a large commercial building located in Belgium is evaluated. A representative office has been instrumented and data on the cooling ceiling system operating in real conditions have been collected. The simulation of the whole system is performed by means of a dynamic thermal model of the building and its HVAC system. The model considers the radiant panels as a dynamic-state finned heat exchanger connected to a simplified lumped dynamic model of the building. The behavior of the radiant ceiling system and the interactions with his environment (walls, ventilated façade, internal loads and ventilation system) has been experimentally and numerically evaluated. Commissioning test results show that the influence of surfaces temperatures inside the room, especially the façade, is considerable. Then, it is clear that the radiant ceiling system must be evaluated together with its designed environment and not as separate HVAC equipment. [less ▲]

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See detailA dynamic unfolded protein response contributes to the control of cortical neurogenesis
LAGUESSE, Sophie ULg; Creppe, Catherine ULg; Nedialkova, Dany et al

in Developmental Cell (2015)

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See detailA dynamic Unfolded Protein Response controls cortical neurogenesis
Creppe, Catherine ULg; Laguesse, Sophie; Nedialkova, Dany et al

Poster (2015)

Detailed reference viewed: 8 (1 ULg)
See detailA dynamic Unfolded Protein Response controls cortical neurogenesis
Creppe, Catherine ULg; Laguesse, sophie; Nedialkova, Dany et al

Poster (2015)

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See detailA dynamic upper atmosphere of Venus as revealed by VIRTIS on Venus Express
Drossart, P.; Piccioni, G.; Gérard, Jean-Claude ULg et al

in Nature (2007), 450

The upper atmosphere of a planet is a transition region in which energy is transferred between the deeper atmosphere and outer space. Molecular emissions from the upper atmosphere (90-120 km altitude) of ... [more ▼]

The upper atmosphere of a planet is a transition region in which energy is transferred between the deeper atmosphere and outer space. Molecular emissions from the upper atmosphere (90-120 km altitude) of Venus can be used to investigate the energetics and to trace the circulation of this hitherto little-studied region. Previous spacecraft(1) and ground-based(2-4) observations of infrared emission from CO2, O-2 and NO have established that photochemical and dynamic activity controls the structure of the upper atmosphere of Venus. These data, however, have left unresolved the precise altitude of the emission(1) owing to a lack of data and of an adequate observing geometry(5,6). Here we report measurements of day-side CO2 non-local thermodynamic equilibrium emission at 4.3 mu m, extending from 90 to 120 km altitude, and of night-side O-2 emission extending from 95 to 100 km. The CO2 emission peak occurs at similar to 115 km and varies with solar zenith angle over a range of similar to 10 km. This confirms previous modelling(7), and permits the beginning of a systematic study of the variability of the emission. The O-2 peak emission happens at 96 km +/- 1 km, which is consistent with three-body recombination of oxygen atoms transported from the day side by a global thermospheric sub-solar to anti-solar circulation, as previously predicted(8). [less ▲]

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See detailDynamical atomic charges: The case of ABO(3) compounds
Ghosez, Philippe ULg; Michenaud, J. P.; Gonze, X.

in Physical Review. B : Condensed Matter (1998), 58(10), 6224-6240

Based on recent first-principles computations in perovskite compounds, especially BaTiO3, we examine the significance of the Born effective charge concept and contrast it with other atomic charge ... [more ▼]

Based on recent first-principles computations in perovskite compounds, especially BaTiO3, we examine the significance of the Born effective charge concept and contrast it with other atomic charge definitions, either static (Mulliken, Bader, etc.) or dynamical (Callen, Szigeti, etc.). It is shown that static and dynamical charges are not driven by the same underlying parameters. A unified treatment of dynamical charges in periodic solids and large clusters is proposed. The origin of the difference between static and dynamical charges is discussed in terms of local polarizability and delocalized transfers of charge: local models succeed in reproducing anomalous effective charges thanks to large atomic polarizabilities but, in ABO(3) compounds, ab initio calculations favor the physical picture based upon transfer of charges. Various results concerning barium and strontium titanates are presented. The origin of anomalous Born effective charges is discussed thanks to a band-by-band decomposition which allows us to identify the displacement of the Wannier center of separated bands induced by an atomic displacement. The sensitivity of the Born effective charges to microscopic and macroscopic strains is examined. Finally, we estimate the spontaneous polarization in the four phases of barium titanate. [less ▲]

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See detailDynamical behaviour of electro-mechanical coupled problem
Rochus, Véronique ULg; rixen, Daniel; Golinval, Jean-Claude ULg

Conference (2004)

MEMS are very small devices in which electric as well as mechanical dynamics phenomena appear. Because of the microscopic scale, some strong coupling effects between the different physical fields appear ... [more ▼]

MEMS are very small devices in which electric as well as mechanical dynamics phenomena appear. Because of the microscopic scale, some strong coupling effects between the different physical fields appear, and some forces, which are negligible at macroscopic scales, have to be taken into account. In order to make a good design of these micro-systems, it is important to analyse the coupling between the electrical and mechanical fields. This paper concerns the modelling of the strong electromechanical coupling appearing in micro-electro-mechanical systems (MEMS). The finite element method (FEM) is used to perform dynamical analysis taking into account large mesh displacements. Analysing the vibration of microsystems is a fundamental issues in the design of a broad range of sensors and actuators. The state of the art currently consists in using staggered procedures to compute quasi-static configurations based on the iteration between a structural model loaded by electrostatic forces and an electrostatic model defined on a domain following the deformation of the structure. Staggered iteration then leads to a static equilibrium position. Performing a perturbation analysis around the static equilibrium yields the electromechanical linearized stiffness needed for computing the eigenfrequencies. Obviously, performing the perturbation analysis to evaluate the tangent stiffness for every degree of freedom leads to very high computing costs and therefore onlythe tangent stiffness associated with presumed modes (typically some purely structural modes) are computed. Such a procedure can lead to important inaccuracies for designs where the electrostatic coupling is not quasi-uniform. In our work, we have developed a fully coupled electro-mechanical formulation that allows to find static equilibrium positions in a non-staggered way and which provides fully consistent tangent stiffness matrices for vibration analysis. The efficiency of the approach will be illustrated on modes of micro-electromechanical devices. The results obtained indicate that using this approach pull-in can be computed very accurately and at low computational cost. Also the coupled electromechanical modes obtained in the vicinity of equilibrium positions can be significantly different from the approximations obtained using a structural reduction at forehand. Numerical results are checked against analytical results where appropriate. The formulation developed for the strongly coupled electromechanical problem allows consistent vibration analysis of the system and yields more accurate vibration eigenmodes and frequencies than the classical staggered approaches. A second interest of the coupled tangent matrix is the computation of the dynamical behaviour of the coupled problem when we apply suddenly a voltage to the electrodes. Even under the pull-in voltage, the overshoot of the dynamical response may reduce the distance between the plate so that the electric force becomes dominant and the plates stick together. This phenomenon is called the dynamical pull-in. We will also treat it in this research. [less ▲]

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See detailDynamical clustering in driven granular gas
Opsomer, Eric ULg; Ludewig, François ULg; Vandewalle, Nicolas ULg

in Europhysics Letters [=EPL] (2012), 99

Driven granular gases present rich dynamical behaviors. Due to inelastic collisions, particles may form dense and slow regions. These clusters emerge naturally during a cooling phenomenon but another ... [more ▼]

Driven granular gases present rich dynamical behaviors. Due to inelastic collisions, particles may form dense and slow regions. These clusters emerge naturally during a cooling phenomenon but another dynamical clustering is observed when the system is continuously excited. In this paper, the physical processes that trigger the transition from a granular gas to a dynamical cluster are evidenced through numerical simulations. At the granular scale, the transition is evidenced by the observation of caging effects. At the scale of the system, the transition is emphasized by density fluctuations. Physical arguments, based on relaxation times, provide an analytical prediction for the edge between dynamical regimes. [less ▲]

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See detailDynamical constraints and adiabatic invariants in chemical reactions
Lorquet, Jean-Claude ULg

in Journal of Physical Chemistry A (2007), 111(33), 8050-8055

For long-range electrostatic potentials and, more generally, when the topography of the potential energy surface is locally simple, the reaction path coordinate is adiabatically separable from the ... [more ▼]

For long-range electrostatic potentials and, more generally, when the topography of the potential energy surface is locally simple, the reaction path coordinate is adiabatically separable from the perpendicular degrees of freedom. For the ion-permanent dipole and ion-quadrupole interactions, the Poisson bracket of the adiabatic invariant decreases with the interfragment distance more rapidly than the electrostatic potential. The smaller the translational momentum, the moment of inertia of the neutral fragment, and the dipole or quadrupole moments are, the more reliable the adiabatic approximation is, as expected from the usual argumentation. Closed-form expressions for an effective one-dimensional potential in an adiabatic Hamiltonian are given. Connection with a model where the decoupling is exact is obtained in the limit of an infinitely heavy dipole. The dynamics is also constrained by adiabatic invariance for a harmonic valley about a curved reaction path, as shown by the reaction path Hamiltonian method. The maximum entropy method reveals that, as a result of the invariance properties of the entropy, constraints whose validity has been demonstrated locally only subsist in all parts of phase space. However, their form varies continuously, and they are not necessarily expressed in simple terms as they are in the asymptotic region. Therefore, although the influence of adiabatic invariance has been demonstrated at asymptotically large values of the reaction coordinate only, it persists in more interesting ranges. [less ▲]

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See detailA dynamical energy-based hysteresis model for iron loss calculation in laminated cores
Steentjes, S.; Henrotte, F.; Geuzaine, Christophe ULg et al

in International Journal of Numerical Modelling (2014), 27(3), 433-443

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See detailDynamical evolution of titanium, strontium, and yttrium spots on the surface of the HgMn star HD 11753
Briquet, Maryline ULg; Korhonen, H.; González, J. F. et al

in Astronomy and Astrophysics (2010), 511

<BR /> Aims: We gathered about 100 high-resolution spectra of three typical HgMn (mercury-manganese) stars, <ASTROBJ>HD 11753</ASTROBJ>, <ASTROBJ>HD 53244</ASTROBJ>, and <ASTROBJ>HD 221507</ASTROBJ>, to ... [more ▼]

<BR /> Aims: We gathered about 100 high-resolution spectra of three typical HgMn (mercury-manganese) stars, <ASTROBJ>HD 11753</ASTROBJ>, <ASTROBJ>HD 53244</ASTROBJ>, and <ASTROBJ>HD 221507</ASTROBJ>, to search for slowly pulsating B-like pulsations and surface inhomogeneous distribution of various chemical elements. <BR /> Methods: Classical frequency analysis methods were used to detect line profile variability and to determine the variation period. Doppler imaging reconstruction was performed to obtain abundance maps of chemical elements on the stellar surface. <BR /> Results: For <ASTROBJ>HD 11753</ASTROBJ>, which is the star with the most pronounced variability, distinct spectral line profile changes were detected for Ti, Sr, Y, Zr, and Hg, whereas for <ASTROBJ>HD 53244</ASTROBJ> and <ASTROBJ>HD 221507</ASTROBJ> the most variable line profiles belong to the elements Hg and Y, respectively. We derived rotation periods for all three stars from the variations of radial velocities and equivalent widths of spectral lines belonging to inhomogeneously distributed elements: P[SUB]rot[/SUB] (<ASTROBJ>HD 11753</ASTROBJ>) = 9.54 d, P[SUB]rot[/SUB] (<ASTROBJ>HD 53244</ASTROBJ>) = 6.16 d, and P[SUB]rot[/SUB] (<ASTROBJ>HD 221507</ASTROBJ>) = 1.93 d. For <ASTROBJ>HD 11753</ASTROBJ> the Doppler imaging technique was applied to derive the distribution of the most variable elements Ti, Sr, and Y using two datasets separated by ~65 days. Results of Doppler imaging reconstruction revealed noticeable changes in the surface distributions of Ti II, Sr II, and Y II between the datasets, indicating the hitherto not well understood physical processes in stars with radiative envelopes that cause a rather fast dynamical chemical spot evolution. Based on observations obtained with the CORALIE Echelle Spectrograph on the 1.2-m Euler Swiss telescope, situated at La Silla, Chile.Postdoctoral Fellow of the Fund for Scientific Research, Flanders. [less ▲]

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See detailDynamical Flavor Origin of ZN Symmetries
Aristizabal Sierra, Diego ULg; Vicente, Avelino ULg; Fong, Sheng et al

in Physical Review. D, Particles, Fields, Gravitation, and Cosmology (2015), 91(9),

Discrete Abelian symmetries (ZN) are a common “artifact” of beyond the standard model physics models. They provide different avenues for constructing consistent scenarios for lepton and quark mixing ... [more ▼]

Discrete Abelian symmetries (ZN) are a common “artifact” of beyond the standard model physics models. They provide different avenues for constructing consistent scenarios for lepton and quark mixing patterns, radiative neutrino mass generation as well as dark matter stabilization. We argue that these symmetries can arise from the spontaneous breaking of the Abelian U(1) factors contained in the global flavor symmetry transformations of the gauge-invariant kinetic Lagrangian. This will be the case provided the ultraviolet completion responsible for the Yukawa structure involves scalar fields carrying nontrivial U(1) charges. Guided by minimality criteria, we demonstrate the viability of this approach with two examples: first, we derive the “scotogenic” model Lagrangian, and second, we construct a setup where the spontaneous symmetry-breaking pattern leads to a Z3 symmetry which enables dark matter stability as well as neutrino mass generation at the two-loop order. This generic approach can be used to derive many other models, with residual ZN or ZN1×⋯×ZNk symmetries, establishing an intriguing link between flavor symmetries, neutrino masses and dark matter. [less ▲]

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See detailA dynamical model with hysteresis for the homogenization of ferromagnetic laminated cores
Henrotte, F.; Niyonzima, Innocent ULg; Steentjes, S. et al

in Proceedings of the 7th European Conference on Numerical Methods in Electromagnetism (NUMELEC2012) (2012, July)

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See detailDynamical Modeling of the Deep Impact Dust Ejecta Cloud
Bonev, T.; Ageorges, N.; Bagnulo, S. et al

in Käufl, H. U.; Sterken, C. (Eds.) Deep Impact as a World Observatory Event: Synergies in Space, Time, and Wavelength (2009)

The collision of Deep Impact with comet 9P/Tempel 1 generated a bright cloud of dust which dissipated during several days after the impact. The brightness variations of this cloud and the changes of its ... [more ▼]

The collision of Deep Impact with comet 9P/Tempel 1 generated a bright cloud of dust which dissipated during several days after the impact. The brightness variations of this cloud and the changes of its position and shape are governed by the physical properties of the dust grains. We use a Monte Carlo model to describe the evolution of the post-impact dust plume. The results of our dynamical simulations are compared to the data obtained with FORS2footnote{FORS stands for \underline{FO}cal Reducer and low dispersion Spectrograph for the Very Large Telescope (VLT) of the European Southern Observatory (ESO).} to derive the particle size distribution and the total amount of material contained in the dust ejecta cloud. [less ▲]

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See detailDynamical modeling of the Deep Impact dust ejecta cloud
Bonev, Tanyu; Ageorges, Nancy; Bagnulo, Stefano et al

Report (2007)

The collision of Deep Impact with comet 9P/Tempel 1 generated a bright cloud of dust which dissipated during several days after the impact. The brightness variations of this cloud and the changes of its ... [more ▼]

The collision of Deep Impact with comet 9P/Tempel 1 generated a bright cloud of dust which dissipated during several days after the impact. The brightness variations of this cloud and the changes of its position and shape are governed by the physical properties of the dust grains. We use a Monte Carlo model to describe the evolution of the post-impact dust plume. The results of our dynamical simulations are compared to the data obtained with FORS2, the FOcal Reducer and low dispersion Spectrograph for the VLT of the European Southern Observatory (ESO), to derive the particle size distribution and the total amount of material contained in the dust ejecta cloud. [less ▲]

Detailed reference viewed: 29 (2 ULg)