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Ferroelectric instability in nanotubes and spherical nanoshells Qiu, Ruihao ; Bousquet, Eric ; in Europhysics Letters [=EPL] (2015), 112 The emergence of ferroelectricity in nanotubes and spherical nanoshells is studied theoretically. We determine semi-analytically the size and thickness dependence of the ferroelectric instability, as well ... [more ▼] The emergence of ferroelectricity in nanotubes and spherical nanoshells is studied theoretically. We determine semi-analytically the size and thickness dependence of the ferroelectric instability, as well as its dependence on the properties of the surrounding media and the corresponding interfaces. By properly tuning these factors, we demonstrate possible routes for enhancing the ferroelectric transition temperature and promoting the competition between irrotational and vortex-like states in the ultra-thin limit due to the specific topology of these nanoparticles. [less ▲] Detailed reference viewed: 18 (2 ULg)Leidenfrost drops: effect of gravity Maquet, Laurent ; Brandenbourger, Martin ; et al in Europhysics Letters [=EPL] (2015), 110 Detailed reference viewed: 43 (15 ULg)Capillary-driven two-dimensional buoyancy in vertical soap films Adami, Nicolas ; in Europhysics Letters [=EPL] (2014) Detailed reference viewed: 18 (5 ULg)Constant Froude number in a circular hydraulic jump and its implication on the jump radius selection Duchesne, Alexis ; ; in Europhysics Letters [=EPL] (2014), 107 The properties of a standard hydraulic jump depend critically on a Froude number Fr defined as the ratio of the flow velocity to the gravity waves speed. In the case of a horizontal circular jump, the ... [more ▼] The properties of a standard hydraulic jump depend critically on a Froude number Fr defined as the ratio of the flow velocity to the gravity waves speed. In the case of a horizontal circular jump, the question of the Froude number is not well documented. Our experiments show that Fr measured just after the jump is locked on a constant value that does not depend on the flow rate Q, the kinematic viscosity ν and the surface tension γ. Combining this result with a lubrication description of the outer flow leads, under appropriate conditions, to a new and simple law ruling the jump radius RJ: RJ(ln(R∞))3/8 ∼ Q5/8ν−3/8g−1/8, in excellent agreement RJ with our experimental data. This unexpected result raises an unsolved question to all available models. [less ▲] Detailed reference viewed: 17 (4 ULg)Nuclear forward scattering by the 68.7 keV state of 73Ge in CaGeO3 and GeO2 ; ; et al in Europhysics Letters [=EPL] (2013), 104 Detailed reference viewed: 15 (1 ULg)Xe-129 nuclear resonance scattering on solid Xe and Xe-129 clathrate hydrate ; ; et al in Europhysics Letters [=EPL] (2013), 103(3), 36001-6 Nuclear inelastic and nuclear forward-scattering experiments utilizing the Xe-129 Mossbauer resonance were performed on solid Xe and enriched Xe-129 clathrate hydrate. The lifetime and energy of the ... [more ▼] Nuclear inelastic and nuclear forward-scattering experiments utilizing the Xe-129 Mossbauer resonance were performed on solid Xe and enriched Xe-129 clathrate hydrate. The lifetime and energy of the nuclear resonance were determined to be 1.465(72) ns and 39581.30(4) eV, respectively. Nuclear inelastic scattering spectra could be obtained with an instrumental resolution of 0.93(4) meV. Despite low Lamb-Mossbauer factors, Xe specific densities of phonon states were derived for solid Xe and Xe clathrate hydrate. Their reliability was investigated using 1-phonon terms obtained by fixing Lamb-Mossbauer factor values within the applied Fourier-Log decomposition. ABINIT calculations of the density of phonon states in solid Xe supplement the interpretation of the experimental data for fcc Xe and good agreement with published densities of phonon states could be achieved below 4meV. Results for the Xe clathrate hydrate essentially confirm the rattling nature of the Xe guests and indicate that Xe modes do not contribute to lattice dynamics above 6 meV. Copyright (C) EPLA, 2013 [less ▲] Detailed reference viewed: 36 (4 ULg)Multiple rotations of a drop rolling inside a horizontal circular hydraulic jump Duchesne, Alexis ; ; et al in Europhysics Letters [=EPL] (2013), 102 We explore the complex dynamics of a non-coalescing drop of moderate size inside a circular hydraulic jump of the same liquid formed on a horizontal disk. In this situation the drop is moving along the ... [more ▼] We explore the complex dynamics of a non-coalescing drop of moderate size inside a circular hydraulic jump of the same liquid formed on a horizontal disk. In this situation the drop is moving along the jump and one observes two different motions: a periodic one (it orbits at constant speed) and an irregular one involving reversals of the orbital motion. Modeling the drop as a rigid sphere exchanging friction with liquid across a thin film of air, we rationalize both the orbital motion and the internal rotation of the drop. This internal rotation is evidenced by tracer visualization and exhibits an unexpected dependence upon drop size. [less ▲] Detailed reference viewed: 9 (1 ULg)Dynamical clustering in driven granular gas Opsomer, Eric ; Ludewig, François ; Vandewalle, Nicolas 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 ▲] Detailed reference viewed: 18 (4 ULg)Querying a quasi-classical Oracle: one bit function identification problem implemented in a single atom transistor Fresch, Barbara ; ; et al in Europhysics Letters [=EPL] (2012), 99(2), 28004 Detailed reference viewed: 31 (14 ULg)Nuclear forward and inelastic spectroscopy on 125Te and Sb2 125Te3 2 ; Hermann, Raphaël ; et al in Europhysics Letters [=EPL] (2010) We report on the observation of nuclear forward and nuclear inelastic scattering of synchrotron radiation by Te-125 and the application of both spectroscopic methods to tellurium compounds by using a high ... [more ▼] We report on the observation of nuclear forward and nuclear inelastic scattering of synchrotron radiation by Te-125 and the application of both spectroscopic methods to tellurium compounds by using a high-resolution backscattering sapphire monochromator in combination with fast detection electronics. The lifetime of the nuclear resonance and the energy of the transition were determined to be 2.131(12) ns and 35493.12(30) eV, respectively. As applications, the nuclear inelastic spectrum in Sb2Te3 and the nuclear forward scattering by Te metal were measured. These measurements open the field of nuclear resonance spectroscopy on tellurium compounds such as thermoelectric and superconducting materials. [less ▲] Detailed reference viewed: 20 (3 ULg)Wave propelled ratchets and drifting rafts ; Terwagne, Denis ; et al in Europhysics Letters [=EPL] (2008), 82 Several droplets, bouncing on a vertically vibrated liquid bath, can form various types of bound states, their interaction being due to the waves emitted by their bouncing. Though they associate droplets ... [more ▼] Several droplets, bouncing on a vertically vibrated liquid bath, can form various types of bound states, their interaction being due to the waves emitted by their bouncing. Though they associate droplets which are individually motionless, we show that these bound states are self- propelled when the droplets are of uneven size. The driving force is linked to the assymetry of the emitted surface waves. The direction of this ratchet-like displacement can be reversed, by varying the amplitude of forcing. This direction reversal occurs when the bouncing of one of the drops becomes sub-harmonic. As a generalization, a larger number of bouncing droplets form crystalline rafts which are also shown to drift or rotate when assymetrical. [less ▲] Detailed reference viewed: 53 (27 ULg)Energetic approach for the characterization of taps in granular compaction Ludewig, François ; Dorbolo, Stéphane ; Gilet, Tristan et al in Europhysics Letters [=EPL] (2008), 84(4), We report numerical investigations for the compaction dynamics of dense granular assemblies. The studies are based on the non-smooth contact dynamics model. Our work suggests that the dimensionless ... [more ▼] We report numerical investigations for the compaction dynamics of dense granular assemblies. The studies are based on the non-smooth contact dynamics model. Our work suggests that the dimensionless acceleration parameter Gamma, used by a large majortiy of authors, is not appropriate for rescaling the data. We prove that the dimensionless energy Xi, injected in the granular system at lift-off, is more appropriate and leads to robust interpretations of the compaction dynamics. Indeed, the injected energy allows to pass energy barriers that separate local equilibrium states. Using the Eyring picture of relaxation dynamic, we show that the consideration of Xi leads to a new law for compaction. [less ▲] Detailed reference viewed: 59 (29 ULg)Effects of electromagnetic waves on the electrical properties of contacts between grains Dorbolo, Stéphane ; ; et al in Europhysics Letters [=EPL] (2007), 79(5), A DC electrical current is injected through a chain of metallic beads. The electrical resistance of each bead- bead contacts is measured. At low current, the distribution of these resistances is large and ... [more ▼] A DC electrical current is injected through a chain of metallic beads. The electrical resistance of each bead- bead contacts is measured. At low current, the distribution of these resistances is large and log- normal. At high enough current, the resistance distribution becomes sharp and Gaussian due to the creation of microweldings between some beads. The action of nearby electromagnetic waves ( sparks) on the electrical conductivity of the chain is also studied. The spark effect is to lower the resistance values of the more resistive contacts, the best conductive ones remaining unaffected by the spark production. The spark is able to induce through the chain a current enough to create microweldings between some beads. This explains why the electrical resistance of a granular medium is so sensitive to the electromagnetic waves produced in its vicinity. [less ▲] Detailed reference viewed: 12 (4 ULg)Aging of an antibubble Dorbolo, Stéphane ; ; Vandewalle, Nicolas et al in Europhysics Letters [=EPL] (2005), 69(6), 966-970 Antibubbles are unusual fluid objects consisting of a thin spherical air shell surrounding a liquid globule. Here we study and analyze the aging of these inverted bubbles. The lifetime is found to be ... [more ▼] Antibubbles are unusual fluid objects consisting of a thin spherical air shell surrounding a liquid globule. Here we study and analyze the aging of these inverted bubbles. The lifetime is found to be distributed along an exponential law. Moreover, the breakdown of the air film is observed to be the analogue of dewetting by spinodal decomposition. We interpret the long lifetime of the antibubbles as resulting from the slow drainage of the air until the film reaches a critical thickness. Then, van der Waals forces act, leading to the collapse of the film. [less ▲] Detailed reference viewed: 66 (13 ULg)Decay rates of planar helium ; Schlagheck, Peter ; et al in Europhysics Letters [=EPL] (2005), 70(2), 183-189 We compare the autoionization rates of characteristic configurations of the doubly excited helium atom, in one, two and three dimensions. We find that the decay rates of the two-dimensional restriction ... [more ▼] We compare the autoionization rates of characteristic configurations of the doubly excited helium atom, in one, two and three dimensions. We find that the decay rates of the two-dimensional restriction are in quantitative agreement with those of the real physical system, whilst the one-dimensional model can underestimate the actual decay rates by orders of magnitude. [less ▲] Detailed reference viewed: 10 (1 ULg)Block-to-granular-like transition in dense bubble flows Vandewalle, Nicolas ; Trabelsi, Samy ; Caps, Hervé in Europhysics Letters [=EPL] (2004), 65(3), 316-322 We have experimentally investigated 2-dimensional dense bubble flows underneath inclined planes. Velocity profiles and velocity fluctuations have been measured. A broad second-order phase transition ... [more ▼] We have experimentally investigated 2-dimensional dense bubble flows underneath inclined planes. Velocity profiles and velocity fluctuations have been measured. A broad second-order phase transition between two dynamical regimes is observed as a function of the tilt angle theta. For low theta values, a block motion is observed. For high theta values, the velocity pro. le becomes curved and a shear velocity gradient appears in the flow. [less ▲] Detailed reference viewed: 27 (1 ULg)Non-Gaussian electrical fluctuations in a quasi-2d packing of metallic beads Vandewalle, Nicolas ; Lenaerts, Cedric ; Dorbolo, Stéphane in Europhysics Letters [=EPL] (2001), 53(2), 197-201 The electrical properties of a two-dimensional packing of metallic beads are studied. Small mechanical perturbations of the packing lead to giant voltage fluctuations. Fluctuations are found to be non ... [more ▼] The electrical properties of a two-dimensional packing of metallic beads are studied. Small mechanical perturbations of the packing lead to giant voltage fluctuations. Fluctuations are found to be non-Gaussian and seem to belong to Levy stable distributions. Anticorrelations have been also found for the sign of these fluctuations. [less ▲] Detailed reference viewed: 15 (4 ULg)Nondispersive two-electron wave packets in the collinear driven helium atom Schlagheck, Peter ; in Europhysics Letters [=EPL] (1999), 46(1), 24-30 Nondispersive two-electron wave packets are found in the Floquet spectrum of the driven, one-dimensional helium atom. In classical phase space, they are anchored to the principal nonlinear resonance ... [more ▼] Nondispersive two-electron wave packets are found in the Floquet spectrum of the driven, one-dimensional helium atom. In classical phase space, they are anchored to the principal nonlinear resonance between the collinear frozen planet orbit and the driving field linearly polarized along the orbit. These novel, highly correlated eigenstates of the driven three-body Coulomb problem, exhibit lifetimes of the order of 10(3)...10(7) periods of the driving field, with strong fluctuations reminiscent of chaos-assisted tunneling. [less ▲] Detailed reference viewed: 6 (0 ULg)Different universality classes for SOC in models driven by extremal dynamics Vandewalle, Nicolas ; Ausloos, Marcel in Europhysics Letters [=EPL] (1997), 37(1), 1-6 We investigate a simple growth model. The model considers the growth of trees driven by extremal dynamics. Self-organized criticality (SOC) exhibited by the model is discussed. We point out that this tree ... [more ▼] We investigate a simple growth model. The model considers the growth of trees driven by extremal dynamics. Self-organized criticality (SOC) exhibited by the model is discussed. We point out that this tree-like model does not seem to belong to any already studied SOC universality class. This is shown through a discussion of the dynamics and the so-called gap equation which does not hold here. [less ▲] Detailed reference viewed: 11 (1 ULg)Coulomb interaction and ferroelectric instability of BaTiO3 Ghosez, Philippe ; ; in Europhysics Letters [=EPL] (1996), 33(9), 713-718 Using first-principles calculations, the phonon frequencies at the Gamma-point and the dielectric tensor are determined and analysed for the cubic and rhombohedral phases of BaTiO3. The dipole-dipole ... [more ▼] Using first-principles calculations, the phonon frequencies at the Gamma-point and the dielectric tensor are determined and analysed for the cubic and rhombohedral phases of BaTiO3. The dipole-dipole interaction is then separated a la Cochran from the remaining short-range forces, in order to investigate their respective influence on lattice dynamics. This analysis highlights the delicate balance of forces leading to an unstable phonon in the cubic phase and demonstrates its extreme sensitivity to effective charge changes. Within our decomposition, the stabilization of the unstable mode in the rhombohedral phase or under isotropic pressure has a different origin. [less ▲] Detailed reference viewed: 24 (0 ULg) |
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