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See detailMagnetic flux penetration in Nb superconducting films with lithographically defined micro-indentations
Brisbois, Jérémy ULiege; Adami, Obaïd-Allah ULiege; Avila Osses, Jonathan ULiege et al

in Physical Review B (2016), 93(5), 054521

We present a thorough investigation by magneto-optical imaging of the magnetic flux penetration in Nb thin films with lithographically defined border indentations. We demonstrate that discontinuity lines ... [more ▼]

We present a thorough investigation by magneto-optical imaging of the magnetic flux penetration in Nb thin films with lithographically defined border indentations. We demonstrate that discontinuity lines (d-lines), caused by the abrupt bending of current streamlines around the indentations, depart from the expected parabolic trend close to the defect and depend on the shape and size of the indentation as well as on the temperature. These findings are backed up and compared with theoretical results obtained by numerical simulations and analytical calculations highlighting the key role played by demagnetization effects and the creep exponent n. In addition, we show that the presence of nearby indentations and submicrometer random roughness of the sample border can severely modify the flux front topology and dynamics. Strikingly, in contrast to what has been repeatedly predicted in the literature, we do not observe that indentations act as nucleation spots for flux avalanches, but they instead help to release the flux pressure and avoid thermomagnetic instabilities. [less ▲]

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See detailMagnetic flux transport in the Dungey cycle: A survey of dayside and nightside reconnection rates
Milan, S. E.; Provan, G.; Hubert, Benoît ULiege

in Journal of Geophysical Research. Space Physics (2007), 112(A1),

Changes in the open flux content of the ionospheric polar cap, estimated from auroral, radar, and low-Earth orbit particle measurements, are used to determine dayside and nightside reconnection rates ... [more ▼]

Changes in the open flux content of the ionospheric polar cap, estimated from auroral, radar, and low-Earth orbit particle measurements, are used to determine dayside and nightside reconnection rates during 73 hours of observation spread over nine intervals. We identify 25 episodes of nightside reconnection and examine statistically the rates and durations of reconnection, as well as possible triggers for the onset of reconnection, such as changes in solar wind ram pressure or orientation of the interplanetary magnetic field. Approximately half of the events can possibly be identified with a trigger, the other half appearing spontaneous. On average 0.3 GWb of open flux are closed in each event, with average durations and reconnection rates being 70 min and 85 kV. We find no evidence for a low background rate of nightside reconnection between these events and conclude that substorms and other large reconnection bursts provide the major or only source of flux closure on the nightside. [less ▲]

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See detailMagnetic Fuel Savers
Makaire, Danielle ULiege; Ngendakumana, Philippe ULiege

Report (2007)

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See detailMagnetic ghosts and monopoles
Vandewalle, Nicolas ULiege; Dorbolo, Stéphane ULiege

in New Journal of Physics (2014), 16

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See detailMagnetic guide-wire navigation in pulmonary and systemic arterial catheterization: initial experience in pigs.
Grosse-Wortmann, Lars; Grabitz, Ralf; SEGHAYE, Marie-Christine ULiege

in Journal of Vascular and Interventional Radiology (2007), 18(4), 545-551

PURPOSE: Cardiovascular catheterization can be challenging whenever a stenosis or an abnormal vascular course interferes with probing the target vessel. This study addresses the feasibility of navigating ... [more ▼]

PURPOSE: Cardiovascular catheterization can be challenging whenever a stenosis or an abnormal vascular course interferes with probing the target vessel. This study addresses the feasibility of navigating a guide wire with a magnetic tip by an external magnetic field through pulmonary and systemic arteries in an experimental porcine model. MATERIALS AND METHODS: We investigated six piglets using magnetic guide-wire navigation. Two pulmonary arteriograms were taken from different angles in order to reconstruct the three-dimensional vessel anatomy. A computer interface then calculated three-dimensional coordinates for the vessel in space. Using these coordinates, two external magnets were positioned to create magnetic vectors along the expected vessel course. Magnetically enabled guide wires were then navigated into the vessels using the magnetic field to orient the guide-wire tips. Aortic and renal branches were addressed in a similar fashion. Difficulty in reaching the target vessel was reflected by the number of attempts that were necessary. After 10 failed attempts, the maneuver was recorded to have failed. RESULTS: Thirty-five of 37 (94.6%) arteries with branches at acute angles were reached successfully using magnetic navigation. In two pigs, the left upper lobe artery could not be probed. Peripheral arteries of small diameter were easier to reach than large central arteries, requiring less attempts. CONCLUSIONS: Magnetic guide-wire navigation is feasible in the arteries of the lungs, the head and neck, and the kidneys. It is particularly useful in entering small arterial branches at acute angles and may facilitate interventional therapy in a variety of vascular diseases in children and adults. [less ▲]

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See detailMagnetic hybrid based on iron oxide nanoparticles and thermoresponsive block copolymer for biomedical applications
Sibret, Pierre ULiege; Aqil, Abdelhafid; Zhao, J. et al

Poster (2010, March 18)

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See detailMagnetic hybrid materials for triggered drug delivery and optical properties of intraocular lens
Liu, Ji ULiege; Jérôme, Christine ULiege; Detrembleur, Christophe ULiege et al

Conference (2013, March 20)

Mesoporous silica nanoparticles have great potential for drug delivery system (DDS) due to their large volume for encapsulation of guest molecules in the porous channels. Due to the specific magnetic ... [more ▼]

Mesoporous silica nanoparticles have great potential for drug delivery system (DDS) due to their large volume for encapsulation of guest molecules in the porous channels. Due to the specific magnetic responsiveness, magnetic nanoparticles can penetrate body tissues under a magnetic guidance, providing a potential platform for magnetic-directed DDS. Furthermore, a sharp local heating can be obtained for superparamagnetic nanoparticles when exposed to an alternating magnetic field (AMF). This specific property opens up the possibility of the application in tumor treatments. Here, we fabricated maghemite/SiO2 mesoporous nanohybrids DDS with phase-changed molecules as gate-keepers. The channels were envisaged to be closed in the biological systems during the delivery; however, opened when exposed to external heating or internal heating from hyperthermia generated by the maghemite cores. Thus the uploaded drug can diffuse into the surrounding medium. MTS assay showed a good cytocompatibility of the vehicles in both mouse L929 cells and cancer MEL-5 cells, and also internalization into MEL-5 cells was confirmed by Fluoresce microscopy, fluoresce-activated cell sorting (FACS) and TEM techniques. The release of drugs can be controlled by varying the concentration of the nanohybrids vehicles, the period of AMF treatment, or both. In-vivo triggered-release of doxorubicin into MEL-5 cells was confirmed by the sharp decrease in cell viability. This DDS can be designed for controlled release to an urgent physiological need via chemotherapy, hyperthermia therapy, or both. [less ▲]

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See detailMagnetic hybrid materials for triggered drug delivery and optical properties of intraocular lens
Liu, Ji ULiege; Hurtgen, Marie ULiege; Mornet, Stephan et al

Poster (2012, March 30)

Stimuli-responsive nano-materials have been playing increasingly important roles in the biomedical field due to their ability to alter the physico-chemical properties in response to external stimuli, such ... [more ▼]

Stimuli-responsive nano-materials have been playing increasingly important roles in the biomedical field due to their ability to alter the physico-chemical properties in response to external stimuli, such as temperature, pH, ionic strength, magnetic field, etc. Nanohybrids bearing an inorganic core and thermo-responsive polymer shell are particularly applicable in target delivery and controlled drug release. Poly (N-vinylcaprolactam) (PNVCL) and its copolymers, exhibiting lower critical solution temperature (LCST) where the transition between hydrophilic and hydrophobic state happens, is one of the optimal choices for this core/shell structure. Here we present the in-situ fabrication of thermo-responsive gold nanohybrids coated with a novel poly (vinyl alcohol)-b-poly (N-vinylcaprolactam) (PVOH-b-PNVCL) block copolymers, which were prepared by the cobalt-mediated radical polymerization (CMRP). The interaction between both PVOH and PNVCL segments and gold nanoparticles was confirmed by FT-IR spectra. A sharp thermo-induced phase transition with a good reversibility upon change in temperature was detected by DLS and UV/vis spectrometer. Furthermore, the presence of hydrophilic PVOH moieties endows the gold nanohybrids with improved colloidal stability above LCST without any flocculation detected. This kind of gold nanohybrids can be envisaged as a new drug delivery vehicle. [less ▲]

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See detailMagnetic hysteresis cycle and remnant field distribution of bulk high temperature superconductor / ferromagnet hybrids
Philippe, Matthieu ULiege; Fagnard, Jean-François ULiege; Wera, Laurent ULiege et al

Poster (2013, September)

Bulk (RE)BCO materials can be used potentially as powerful permanent magnets. The magnetic flux distribution above a bulk HTS magnet, however, is strongly non-uniform (conic profile predicted by the Bean ... [more ▼]

Bulk (RE)BCO materials can be used potentially as powerful permanent magnets. The magnetic flux distribution above a bulk HTS magnet, however, is strongly non-uniform (conic profile predicted by the Bean model) compared to the rather flat distribution above a ferromagnet. In the present work, we study how FeNi soft ferromagnetic alloys of different shapes can be combined with a bulk, large grain (RE)BCO superconductor (RE denotes a rare-earth element) to improve the distribution of trapped field at the surface or its average value through the volume of the sample. A FeNi ferromagnetic alloy was machined into pieces of various shapes (cylinders and rings) and attached to (i) the top surface of the bulk HTS cylinder to form bulk ferromagnet / superconductor (F/S) hybrids and (ii) to the top and bottom surfaces to form bulk F/S/F hybrids. The magnetic properties of each hybrid structure were measured under axial magnetic field at 77 K. Pick-up coils wound around the superconductor were used to measure the average magnetic induction inside the superconductor while the remnant induction distribution near the top and bottom surfaces was determined by miniature Hall probe mapping. The modifications of the hysteresis curves and flux distributions were analyzed by taking into account the ferromagnet intrinsic properties (intrinsic permeability, saturation) and geometrical properties (shape, size and volume). The results show that the effect of the ferromagnet increases with its volume. In presence of a ferromagnet, the superconductor hysteresis curve shows a combination of a diamagnetic and a ferromagnetic behaviour on which it is worth noting that (i) the bulk remnant magnetization increases and (ii) in the magnetic saturation regime of the ferromagnet, the magnetic effects of the superconductor and the ferromagnet are superimposed. The results also give evidence that flux lines curve through the ferromagnetic component, which produces a decrease of the self-demagnetizing field inside the superconductor. [less ▲]

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See detailMagnetic kinetic growth-models
Ausloos, Marcel ULiege; Vandewalle, Nicolas ULiege; Cloots, Rudi ULiege

in Journal of Magnetism & Magnetic Materials (1995), 140(Part 3), 2185-2186

Magnetic kinetic growth models are kinetic growth model(s), like the Eden or the DLA models, but allow for the growth to have an extra degree of freedom (a 'spin') which can be coupled to an external ... [more ▼]

Magnetic kinetic growth models are kinetic growth model(s), like the Eden or the DLA models, but allow for the growth to have an extra degree of freedom (a 'spin') which can be coupled to an external field. Two-dimensional simulations show interesting morphologies and parameter dependences. [less ▲]

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See detailMagnetic Massive Stars
Townsend, Rich; Cohen, David H; Dessart, Luc et al

in IAU Symposium (2008, June 01)

Magnetic fields are unexpected in massive stars, due to the absence of a sub-surface convective dynamo. However, advances in instrumentation over the past three decades have led to their detection in a ... [more ▼]

Magnetic fields are unexpected in massive stars, due to the absence of a sub-surface convective dynamo. However, advances in instrumentation over the past three decades have led to their detection in a small but growing subset of these stars. Moreover, complementary theoretical developments have highlighted their potentially significant influence over the structure, evolution and circumstellar environments of massive stars. Here, we summarize a special session convened prior to the main conference, focused on presenting recent developments in the study of massive-star magnetic fields. [less ▲]

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See detailMagnetic Model Refinement via a Coupling of Finite Element Subproblems
Dular, Patrick ULiege; Vazquez Sabariego, Ruth; Krähenbühl, Laurent et al

in Scientific Computing in Electrical Engineering (2012)

Model refinements of magnetic circuits are performed via a subdomain finite element method. A complete problem is split into subproblems with overlap- ping meshes, to allow a progression from source to ... [more ▼]

Model refinements of magnetic circuits are performed via a subdomain finite element method. A complete problem is split into subproblems with overlap- ping meshes, to allow a progression from source to reaction fields, ideal to real flux tubes, 1-D to 3-D models, perfect to real materials, statics to dynamics, with any coupling of these changes. Its solution is then the sum of the subproblem solutions. The procedure simplifies both meshing and solving processes, and quantifies the gain given by each refinement on both local fields and global quantities. [less ▲]

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See detailMagnetic model refinement via a coupling of finite element subproblems
Dular, Patrick ULiege; V Sabariego, Ruth ULiege; Krähenbühl, Laurent et al

in Proceedings of Scientific Computing in Electrical Engineering (SCEE 2010) (2010)

Model refinements of magnetic circuits are performed via a subdomain finite element method. A complete problem is split into subproblems with overlap- ping meshes, to allow a progression from source to ... [more ▼]

Model refinements of magnetic circuits are performed via a subdomain finite element method. A complete problem is split into subproblems with overlap- ping meshes, to allow a progression from source to reaction fields, ideal to real flux tubes, 1-D to 3-D models, perfect to real materials, statics to dynamics, with any coupling of these changes. Its solution is then the sum of the subproblem solutions. The procedure simplifies both meshing and solving processes, and quantifies the gain given by each refinement on both local fields and global quantities. [less ▲]

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See detailMagnetic model refinement via a perturbation finite element method – from 1D to 3D
Dular, Patrick ULiege; V Sabariego, Ruth ULiege; Krähenbühl, Laurent

in COMPEL (2009), 28(4), 974-988

Purpose – The purpose of this paper is to develop a sub-domain perturbation technique for refining magnetic circuit models with finite element (FE) models of different dimensions. Design/methodology ... [more ▼]

Purpose – The purpose of this paper is to develop a sub-domain perturbation technique for refining magnetic circuit models with finite element (FE) models of different dimensions. Design/methodology/approach – A simplified problem considering ideal flux tubes is first solved, as either a 1D magnetic circuit or a simplified FE problem. Its solution is then corrected via FE perturbation problems considering the actual flux tube geometry and the exterior regions, that allow first 2D and then 3D leakage fluxes. Each of these sub-problems requires an appropriate proper volume mesh, with no need of interconnection. The solutions are transferred from one problem to the other through projections of source fields between meshes. Findings – The developed perturbation FE method allows to split magnetic circuit analyses into subproblems of lower complexity with regard to meshing operations and computational aspects. A natural progression from simple to more elaborate models, from 1D to 3D geometries, is thus possible, while quantifying the gain given by each model refinement and justifying its utility. Originality/value – Approximate problems with ideal flux tubes are accurately corrected when accounting for leakage fluxes via surface sources of perturbations. The constraints involved in the subproblems are carefully defined in the resulting FE formulations, respecting their inherent strong and weak nature. As a result, an efficient and accurate computation of local fields and global quantities, i.e. flux, MMF, reluctance, is obtained. The method is naturally adapted to parameterized analyses on geometrical and material data. [less ▲]

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See detailMagnetic moment and local magnetic induction of superconducting/ferromagnetic structures subjected to crossed fields: experiments on GdBCO and modelling
Fagnard, Jean-François ULiege; Morita, Mitsuru; Nariki, Shinya et al

in Superconductor Science and Technology (2016), 29(12), 125004

Recent studies have shown that ferromagnetic materials can be used together with bulk high temperature superconductors in order to improve their magnetic trapped field. Remarkably, it has also been ... [more ▼]

Recent studies have shown that ferromagnetic materials can be used together with bulk high temperature superconductors in order to improve their magnetic trapped field. Remarkably, it has also been pointed out that ferromagnets can help in reducing the crossed field effect, namely the magnetization decay that is observed under the application of AC transverse magnetic fields. In this work, we pursue a detailed study of the influence of the geometry of the ferromagnetic part on both trapped fields and crossed field effects. The magnetic properties of the hybrid superconducting/soft ferromagnetic structures are characterized by measuring the magnetic moment with a bespoke magnetometer and the local magnetic field density with Hall probes. The results are interpreted by means of 2D and 3D numerical models yielding the distribution of the superconducting currents as a function of the ferromagnet geometry. We examine in details the distortion of the shielding superconducting currents distribution in hybrid structures subjected to crossed magnetic fields. These results confirm the existence of an optimum thickness of the ferromagnet, which depends on the saturation magnetization of the ferromagnetic material and the current density of the superconductor. A hybrid structure providing an efficient protection against the crossed magnetic field while maintaining the magnetic induction along the axis of the structure is suggested. The limitations of the 2D modelling in this configuration are discussed. [less ▲]

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See detailMagnetic nanoparticles coated by temperature responsive copolymers for hyperthermia
Aqil, Abdelhafid ULiege; Vasseur, Sébastien; Duguet, Etienne et al

in Journal of Materials Chemistry (2008), 18(28), 3352-3360

Various temperature-responsive N-isopropylacrylamide-based functional copolymers were prepared and used for the stabilization of iron oxide nanoparticles. The copolymers investigated are poly(acrylic acid ... [more ▼]

Various temperature-responsive N-isopropylacrylamide-based functional copolymers were prepared and used for the stabilization of iron oxide nanoparticles. The copolymers investigated are poly(acrylic acid)-b-poly(N-isopropylacrylamide) (PAA-PNIPAM) and poly(acrylic acid)-b-poly(N-isopropylacrylamide)-b-poly(acrylate methoxy poly(ethylene oxide)) (PAA-PNIPAM-PAMPEO), with different molecular weights. The coated nanoparticles were characterized in terms of size by a combination of dynamic light scattering (DLS) and transmission electron microscopy (TEM). A sharp temperature transition was confirmed by particle size measurements vs. temperature. In addition, the stealthiness of the coated nanoparticles has been assessed in vitro by the haemolytic CH50 test. These measurements evidenced the crucial role of the PEO segments on the stealthiness of the nanoparticles and thus that such copolymers are particularly suitable for biomedical applications. Preliminary experiments of alternating magnetic field induced heating were performed and specific absorption rates of the various samples were recorded. [less ▲]

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See detailMagnetic Ordering in Nitrides with the η-Carbide Structure: (Ni,Co,Fe)2(Ga,Ge)Mo3N
Sviridov, A; Battle, Peter D.; Grandjean, Fernande ULiege et al

in Inorganic Chemistry (2010), 491

Compositions in the series Ni2-xCoxGeMo3N (0 ex e2),Co2Ge1-xGaxMo3N (0<x e0.7),Co2-xFexGeMo3N (0 e x e 2), and Co2-xFexGe0.5Ga0.5Mo3N (0 e x e 0.8) have been synthesized by the reductive nitridation of ... [more ▼]

Compositions in the series Ni2-xCoxGeMo3N (0 ex e2),Co2Ge1-xGaxMo3N (0<x e0.7),Co2-xFexGeMo3N (0 e x e 2), and Co2-xFexGe0.5Ga0.5Mo3N (0 e x e 0.8) have been synthesized by the reductive nitridation of binary oxides and studied by appropriate combinations of magnetometry, transport measurements, neutron diffraction, and M€ossbauer spectroscopy. All of these compositions adopt the cubic η-carbide structure (a ∼ 11.11 A ̊ ) and show a resistivity of ∼10 -3 Ω cm. No long-range magnetic order was observed in Ni 2-xCoxGeMo3N, although evidence of spin freezing was observed in Co2GeMo3N. The introduction of gallium into this composition leads to the onset of antiferromagnetic ordering at 90 K in Co2Ge0.3Ga0.7Mo3N. The magnetic structure consists of an antiferromagnetic arrangement of ferromagnetic Co4 groups, with an ordered magnetic moment of 0.48(9) μB per cobalt atom. The same magnetic structure is found in Co0.5Fe1.5GeMo3N and Co1.2Fe0.8Ge0.5Ga0.5Mo3N. The former orders above room temperature with an average moment of 1.08(3) μB per transition-metal site, and the latter at 228 K with an average moment of 1.17(4) μB per site. The magnetic behavior of these compounds is discussed in terms of the electron count within each series. [less ▲]

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See detailMagnetic ordering in U2Pd2In and U2Pd2Sn
Purwanto, A.; Robinson, R. A.; Havela, Ladislav et al

in Physical Review. B : Condensed Matter (1994), 50(10), 6792-6801

The tetragonal intermetallic compounds U2Pd2In and U2Pd2Sn have been studied by means of magnetic susceptibility, magnetization, specific heat, electrical resistivity, and x-ray- and neutron-diffraction ... [more ▼]

The tetragonal intermetallic compounds U2Pd2In and U2Pd2Sn have been studied by means of magnetic susceptibility, magnetization, specific heat, electrical resistivity, and x-ray- and neutron-diffraction techniques. The compounds order antiferromagnetically at 36 and 41 K, respectively, and have enhanced electronic specific-heat coefficients γ of 393 and 203 mJ/mol f.u. K**2, respectively. At low temperature, the nearest-neighbor U-U spacing is along the c axis in both compounds, though in U2Pd2Sn the in-plane U-U distance is shorter at room temperature. This crossover is due to motion of the U atoms within the cell rather than anisotropy of the thermal contraction. It is now well established in several classes of (1:1:1) uranium ternary intermetallic compounds that the strong magnetic anisotropy is correlated with the direction of nearest-neighbor U-U links; the moments are almost invariably oriented perpendicular to such links. This is also the case for U2Pd2In and U2Pd2Sn, where the moments lie in the tetragonal basal plane in a canted arrangement along [110] and [1¯10] directions. Of four such Shubnikov subgroups of P4/mbm, one is clearly preferred by the data. At 10 K, the magnetic moments extracted are (1.6±0.2) Bohr magneton and (2.0±0.1) Bohr magneton per U atom in U2Pd2In and U2Pd2Sn, respectively. [less ▲]

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