ORBi Collection: Physics
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Speed limit to the Abrikosov lattice in mesoscopic superconductors
http://hdl.handle.net/2268/184340
Title: Speed limit to the Abrikosov lattice in mesoscopic superconductors
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<br/>Author, co-author: Grimaldi, Gaia; Leo, Antonio; Sabatino, P.; Carapella, G.; Nigro, Angela; Pace, Sandro; Moshchalkov, Victor V.; Silhanek, Alejandro
<br/>
<br/>Abstract: We study the instability of the superconducting state in a mesoscopic geometry for the low
pinning material Mo3Ge characterized by a large Ginzburg-Landau parameter. We observe that in the current driven switching to the normal state from a nonlinear region of the Abrikosov flux
flow, the mean critical vortex velocity reaches a limiting maximum velocity as a function of the applied magnetic fi eld. Based on time dependent Ginzburg-Landau simulations we argue that the observed behavior is owed to the high velocity vortex dynamics confi ned on a mesoscopic scale. We build up a general phase diagram which includes all possible dynamic confi gurations of Abrikosov lattice in a mesoscopic superconductor.Long-wave infrared digital holographic interferometry for deformation measurement of the segmented detector array of the space EUCLID mission
http://hdl.handle.net/2268/184316
Title: Long-wave infrared digital holographic interferometry for deformation measurement of the segmented detector array of the space EUCLID mission
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<br/>Author, co-author: Vandenrijt, Jean-François; Thizy, Cédric; Beaumont, Florent; Garcia, José; Martin, Laurent; Fabron, Christophe; Prieto, Eric; Maciaszek, Thierry; Georges, Marc
<br/>
<br/>Abstract: Digital holographic interferometry in LWIR is used for following the deformation and relative movement of an assembly of detectors to be used in space. The setup is incorporated in a vacuum chamber for cryogenic testing.Optical study of diﬀraction grating/Fresnel lens combinations applied to a spectral-splitting solar concentrator for space applications
http://hdl.handle.net/2268/184304
Title: Optical study of diﬀraction grating/Fresnel lens combinations applied to a spectral-splitting solar concentrator for space applications
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<br/>Author, co-author: Michel, Céline; Loicq, Jerôme; Thibert, Tanguy; Habraken, Serge
<br/>
<br/>Abstract: This paper presents a new design of a planar solar concentrator with spectral splitting of light for space applications. This concentrator spectrally splits the incident light into mainly two parts. Each part is then focused onto speciﬁc spatially separated photovoltaic cells, allowing for independent control of respective cells output power. These advantages of both spectral splitting and light focusing are here combined thanks to a speciﬁc diﬀraction grating superimposed on a Fresnel lens. The theoretical principle of the optical design is presented, with optimization of each element and improvement steps, including optimization of grating period evolution along the lens, and testing of two kinds of gratings (a blazed and a lamellar one). First numerical results are presented, highlighting the possibility to design a concentrator at about 10× or more for each cell, with an output power larger than that of a classical concentrator focusing on a GaAs SJ cell, and less than 10% of losses for tracking errors up to ±0.8°. Some experimental results are also presented.Rheological behavior of β-Ti and NiTi powders produced by atomization for SLM production of open porous orthopedic implants
http://hdl.handle.net/2268/184302
Title: Rheological behavior of β-Ti and NiTi powders produced by atomization for SLM production of open porous orthopedic implants
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<br/>Author, co-author: Yablokova, G.; Speirs, M.; Van Humbeeck, J.; Kruth, J.-P.; Schrooten, J.; Cloots, Rudi; Boschini, Frédéric; Lumay, Geoffroy; Luyten, J.
<br/>
<br/>Abstract: The growing interest for Selective Laser Melting (SLM) in orthopedic implant manufacturing is accompanied by
the introduction of novel Ti alloys, in particular β-Ti for their excellent corrosion resistance as well as favorable
combination of high mechanical strength, fatigue resistance and relatively low elastic modulus. As part of the
SLM process for producing quality β-Ti parts powder flowability is essential to achieve uniform thickness of powder
layers. In this work the flowability of different gas atomized β-Ti, including NiTi, powders has been studied. Their
rheological properties were compared to those of commercially available plasma-atomized Ti–6Al–4V powder
using a newly developed semi-automatic experimental set-up. Not only the particle size, shape and size distribution
of the powders display a large influence on the powder flowability but also particle surface properties such as
roughness, chemical composition and the presence of liquid on the surface of the particles. It was found that plasma
or gas atomization production techniques for SLM powder have a considerable effect on the particle topography.
Among the powders studied regarding SLM applicability only rheological properties of the fine size fraction
(25–45 μm) of Ti–45Nb didn't conform to SLM processing requirements. To improve flowability of the Ti–45Nb
powder itwas annealed both in air and argon atmosphere at 600 °C during 1 h, resulting in an improved rheological
behavior suitable for SLM processing.Quantitatively mimicking wet colloidal suspensions with dry granular media
http://hdl.handle.net/2268/184301
Title: Quantitatively mimicking wet colloidal suspensions with dry granular media
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<br/>Author, co-author: Messina, René; Aljawhari, Sarah; Bécu, Lydiane; Schockmel, Julien; Lumay, Geoffroy; Vandewalle, Nicolas
<br/>
<br/>Abstract: Athermal two-dimensional granular systems are exposed to external mechanical noise leading to
Brownian-like motion. Using tunable repulsive interparticle interaction, it is shown that the same
microstructure as that observed in colloidal suspensions can be quantitatively recovered at a
macroscopic scale. To that end, experiments on granular and colloidal systems made up of
magnetized particles as well as computer simulations are performed and compared. Excellent
agreement throughout the range of the magnetic coupling parameter Γ is found for the pair
distribution as well as the bond-orientational correlation functions. This finding opens new ways to
efficiently and very conveniently explore phase transitions, crystallization, nucleation, etc in confined
geometries.Development of mobile analytical methods for Cultural Heritage objects
http://hdl.handle.net/2268/184043
Title: Development of mobile analytical methods for Cultural Heritage objects
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<br/>Author, co-author: Hocquet, François-PhilippeEffective heat conduction in dispersion of wires
http://hdl.handle.net/2268/183738
Title: Effective heat conduction in dispersion of wires
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<br/>Author, co-author: Behrang, Arash; grmela, miroslav; Dubois, Charles; Turenne, S; lafleur, P.G.; Lebon, GeorgyHeat conduction at micro and nanoscales: A review through the prism of Extended Irreversible Thermodynamics
http://hdl.handle.net/2268/183734
Title: Heat conduction at micro and nanoscales: A review through the prism of Extended Irreversible Thermodynamics
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<br/>Author, co-author: Lebon, GeorgyElectrically charged droplet: Case study of a simple generator
http://hdl.handle.net/2268/183623
Title: Electrically charged droplet: Case study of a simple generator
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<br/>Author, co-author: Brandenbourger, Martin; Dorbolo, StéphaneImproving CKM Unitary Limits via Low-Energy Nuclear Physics
http://hdl.handle.net/2268/183595
Title: Improving CKM Unitary Limits via Low-Energy Nuclear Physics
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<br/>Author, co-author: Finlay, Paul; Ball, G.; Bastin, Thierry; Bissel, Marc; Ettenauer, S.; Glover, Rohan; Naviliat-Cuncic, O.; Neyens, Gerda; Rand, E.; Severijns, Nathal; Svensson, C.; Velten, P.; Zákoucký, D.Multiqubit symmetric states with maximally mixed one-qubit reductions
http://hdl.handle.net/2268/183481
Title: Multiqubit symmetric states with maximally mixed one-qubit reductions
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<br/>Author, co-author: Baguette, Dorian; Bastin, Thierry; Martin, John
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<br/>Abstract: We present a comprehensive study on the remarquable properties shared by maximally entangled symmetric states of arbitrary numbers of qubits in the sense of the maximal mixedness of the one-qubit reduced density operator. Such states are of great interest in quantum information as they maximize several measures of entanglement, such as Meyer-Wallach entropy [1] and any entanglement monotone based on linear homogenous positive functions of pure state within their SLOCC classes of states [2, 3]. When they exist, they are unique up to local unitaries within their SLOCC classes [3, 4]. They play a specific role in the determination of the local unitary equivalence of multiqubit states [5]. Moreover, they are maximally fragile (in the sense that they are the states which are the most sensitive to noise) and have therefore been proposed as ideal candidates for ultrasensitive sensors [6]. They appear in the litterature under various names : maximally entangled states [6], 1-uniform states [7], normal forms [3, 4] and nongeneric states [5].
We present a general criterion to easily identify whether given symmetric states are maximally entangled or not [9]. We show that these maximally entangled symmetric (MES) states are the only symmetric states for which the expectation value of the associated collective spin S of the system vanishes, which coincides with the definition of anticoherence to order one of spin states. This definition also coincides with the cancellation of the dipole moment of the Husimi function of the state. We then generalize these properties and show that a state is anticoherent to order t, <(S.n)^k> is independent of n for k = 1, . . . , t, where n is a unit vector, iff it has maximally mixed t-qubit reductions or iff all moments up to order 2t of its Husimi function vanish. We also establish the equivalence between anticoherent states to order t and unpolarized light states to order t [8], thereby encompassing various state characterizations under the same banner [9, 10].
We provide a nonexistence criterion allowing us to know immediately whether SLOCC classes of symmetric states can contain MES states or not. We show in particular that the symmetric Dicke state SLOCC classes never contain such MES states, with the only exception of the balanced Dicke state class for even numbers of qubits. We analyze the 4-qubit system exhaustively and identify and characterize all MES states of this system as well as the only 4-qubit state anticoherent to order 2. Finally, we analyze the entanglement content of MES states with respect to the geometric [11] and barycentric [12] measures of entanglement.
[1] D. A. Meyer and N. R. Wallach, J. Math. Phys. 43, 4273 (2002).
[2] Classes of states equivalent through stochastic local operations with classical communication.
[3] F. Verstraete, J. Dehaene, and B. De Moor, Phys. Rev. A 68, 012103 (2003).
[4] G. Gour and N. Wallach, N. J. Phys. 13, 073013 (2011).
[5] B. Kraus, Phys. Rev. Lett. 104, 020504 (2010).
[6] N. Gisin and H. Bechmann-Pasquinucci, Phys. Lett. A 246, 1 (1998).
[7] A. J. Scott, Phys. Rev. A 69, 052330 (2004).
[8] L. L. Sánchez-Soto, A. B. Klimov, P. de la Hoz, and G. Leuchs J. Phys. B : At. Mol. Opt. Phys. 46, 104011 (2013).
[9] D. Baguette, T. Bastin, and J. Martin, Phys. Rev. A 90, 032314 (2014).
[10] O. Giraud, D. Braun, D. Baguette, T. Bastin, and J. Martin, arXiv :1409.1106.
[11] T.-C. Wei and P. M. Goldbart, Phys. Rev. A 68, 042307 (2003).
[12] W. Ganczarek, M. Kus, and K. Zyczkowski, Phys. Rev. A 85, 032314 (2012).Towards precision β-decay measurements with laser cooled 35Ar
http://hdl.handle.net/2268/183438
Title: Towards precision β-decay measurements with laser cooled 35Ar
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<br/>Author, co-author: Glover, Rohan; Lenaers, Florence; Velten, Philippe; Finlay, Paul; Couratin, C.; Hayen, L.; Severijns, Nathal; Bastin, ThierryTest of atmospheric neutrons effects on FPGA at Centre Spatial de Liège (CSL) – Université de Liège (ULg)
http://hdl.handle.net/2268/183403
Title: Test of atmospheric neutrons effects on FPGA at Centre Spatial de Liège (CSL) – Université de Liège (ULg)
<br/>
<br/>Author, co-author: Carapelle, AlainOptical collimation of an atomic beam using a white light molasses
http://hdl.handle.net/2268/183355
Title: Optical collimation of an atomic beam using a white light molasses
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<br/>Author, co-author: Glover, Rohan; Bastin, ThierryOperational entanglement families of symmetric mixed N-qubit states
http://hdl.handle.net/2268/183354
Title: Operational entanglement families of symmetric mixed N-qubit states
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<br/>Author, co-author: Bastin, Thierry; Mathonet, Pierre; Solano, EnriqueAnticoherence of multiqubit symmetric states
http://hdl.handle.net/2268/183348
Title: Anticoherence of multiqubit symmetric states
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<br/>Author, co-author: Baguette, Dorian; Bastin, Thierry; Martin, JohnThermoelectric properties of two stacking sequences of crystalline GST-225
http://hdl.handle.net/2268/183312
Title: Thermoelectric properties of two stacking sequences of crystalline GST-225
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<br/>Author, co-author: Ibarra Hernandez, Wilfredo; Raty, Jean-Yves
<br/>
<br/>Abstract: Pseudobinary GeTe-Sb2Te3 compounds are widely used as phase-change
optical materials for DVD-RAM.[3] Ge2Sb2Te5 (GST-225) is used for
this propose but the stacking sequence of the stable crystal structure
is motive of debate. Pseudobinary compounds there are claimed to be
good thermoelectric materials due the large number of intrinsic structural
vacancies.[4] Thermoelectric properties for two proposed stacking sequences of GST-225 are computed using DFT[5, 6] and Boltzmann transport equation in the constant relaxation time approximation. After phonon calculations, no dynamic instabilities were found in the Irreducible Brillouin Zone for either of the proposed stacking sequences. One of the stacking sequences shows semiconductor-like density of states (DOS) with a computed gap of 190 meV unlike the other stacking sequence which has a metallic-like DOS. Thermoelectric properties calculation
reveals that semiconductor-like structure has the highest value of Seebeck coeffcient (SC).Ab Initio DFT study of electronic and thermoelectric properties of crystalline Ge2Sb2Te5
http://hdl.handle.net/2268/183311
Title: Ab Initio DFT study of electronic and thermoelectric properties of crystalline Ge2Sb2Te5
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<br/>Author, co-author: Ibarra Hernandez, Wilfredo; Raty, Jean-Yves
<br/>
<br/>Abstract: Pseudo-binary phase change materials such as (GeTe)n/(Sb2Te3)m have been recently considered for thermoelectric applications. Among these, Ge2Sb2Te5 (GST225, n=2 and m=1) is very popular as it is the leading candidate for non-volatile memory devices such as phase change random access memory. It is well know that the stable crystal structure of GST225 is hexagonal, with atomic layers stacked in the c direction. The stacking sequence is however still under some debate, and structures varying from conventional semiconductor to Dirac semimetal have been claimed to differ only by the nature of the stacking sequence. Here we present electronic, dynamic and thermoelectric calculations on three different stacking sequences of crystalline GST225. We use ab-initio DFT calculations together with Boltzmann transport equations to access thermoelectric properties within the constant relaxation time approximation. Our results show that all three proposed stacking sequences are (meta-)stable. From the density of states we determine that two structures are metallic while the most stable structure has a 0.35 eV band gap. Above 100K, the computed Seebeck coefficient seems to indicate that the experimentally observed structure is the Dirac semimetal one, the doping level being of the order of 1 × 1020 cm−3.leidenfrost drops
http://hdl.handle.net/2268/183302
Title: leidenfrost drops
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<br/>Author, co-author: sobac, benjamin; rednikov, alexey; Dorbolo, Stéphane; colinet, pierreStability and Aging of Phase Change Materials : An Ab Initio Perspective
http://hdl.handle.net/2268/183300
Title: Stability and Aging of Phase Change Materials : An Ab Initio Perspective
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<br/>Author, co-author: Raty, Jean-Yves
<br/>
<br/>Abstract: Data recording with Phase Change Materials is a much studied topic as the writing/erasing characteristics, cyclability and downscaling properties of these materials allow for efficient data storage in future generations of devices. Nevertheless, some aspects of phase change materials are limiting their performances and delaying their wider technological application.
First, aging phenomena are common to all amorphous structures, but of special importance PCMs since it impedes the realization of multi-level memories. Different interpretations have been proposed, but we focus here on the structural relaxation of amorphous GeTe, chosen because it is the simplest system that is representative of the wider class of GST alloys, lying along the GeTe-Sb2Te3 composition line of the GeSbTe phase diagram. One difficulty encountered in the simulation of these amorphous systems is that the direct generation of an amorphous structure by quenching a liquid using Density Functional Theory (DFT) based Molecular Dynamics leads to one sample with a small number of atoms, and, hence of small number of atomic environments. Here we sample a large number of local atomic environments, corresponding to different bonding schemes, by chemically substituting different alloys, selected to favor different local atomic structures. This enables spanning a larger fraction of the configuration space relevant to aging. Our results support a model of the amorphous phase and its time evolution that involves an evolution of the local (chemical) order towards that of the crystal. On the other hand its electronic properties drift away from those of the crystal, driven by an increase of the Peierls-like distortion of the local environments in the amorphous, as compared to the crystal [1].
A second problem faced by PCMs is the fact that data recording is limited at high temperature due to the increased propensity to recrystallize. One approach to counter this is to stabilize the PCM using impurity atoms such as C or N. Using DFT and the analysis of the mechanical properties (constraints theory), we demonstrate how these impurity atoms modify the rigidity of the network, which is experimentally correlated with the activation energy for crystallization [2].
Finally, the crystal phase itself has been shown to have variable conductivities depending on the thermal history and annealing conditions. If this could be used profitably for multi-level recording, it also indicates that the crystal is undergoes some temporal evolution. Using DFT, we clarify the stability behavior of GST crystal and show that the metal-insulator transition is driven by the migration of intrinsic vacancies and an Anderson localization transition [3].
[1] J.Y Raty, W. Zhang, J. Luckas, C. Chen, R. Mazzarello, C. Bichara and M. Wuttig, Nat. Comm. (2015)
[2] G. Ghezzi, J.Y. Raty, S. Maitrejean, A. Roule, E. Elkaim and F. Hippert, Applied Physics Letters, 99 (2011) 151906
[3] W. Zhang, A. Thiess, P. Zalden, R. Zeller, P. H. Dederichs, J-Y. Raty, M.Wuttig, S. Blügel et R. Mazzarello, Nature Materials 11 (2012) 952