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See detailMagnetic shielding properties of a superconducting hollow cylinder containing slits: Modelling and experiment
Fagnard, Jean-François ULg; Elschner, S.; Hobl, A. et al

in Superconductor Science and Technology (2012), 25(10), 104006

This paper deals with the magnetic properties of bulk high temperature superconducting cylinders used as magnetic shields. We investigate, both numerically and experimentally, the magnetic properties of a ... [more ▼]

This paper deals with the magnetic properties of bulk high temperature superconducting cylinders used as magnetic shields. We investigate, both numerically and experimentally, the magnetic properties of a hollow cylinder with two axial slits which cut the cylinder in equal halves. Finite element method modelling has been used with a three-dimensional geometry to help us in understanding how the superconducting currents flow in such a cut cylinder and therefore how the magnetic shielding properties are affected, depending on the magnetic field orientation. Modelling results show that the slits block the shielding current flow and act as an entrance channel for the magnetic flux lines. The contribution of the slits to the total flux density that enters the cylinder is studied through the angle formed between the applied field and the internal field. The modelled data agree nicely with magnetic shielding properties measured on a bulk Bi-2212 hollow cylinder at 77K. The results demonstrate that the magnetic flux penetration in such a geometry can be modelled successfully using only two parameters of the superconductor (constant J c and n value), which were determined from magnetic measurements on the plain cylinder. © 2012 IOP Publishing Ltd. [less ▲]

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See detailMagnetic shielding properties of high- Tc superconducting hollow cylinders: model combining experimental data for axial and transverse magnetic field configurations
Fagnard, Jean-François ULg; Dirickx, Michel; Ausloos, Marcel ULg et al

in Superconductor Science and Technology (2009), 22(10), 10500210

Magnetic shielding efficiency was measured on high- Tc superconducting hollow cylinders subjected to either an axial or a transverse magnetic field in a large range of field sweep rates, dBapp/dt. The ... [more ▼]

Magnetic shielding efficiency was measured on high- Tc superconducting hollow cylinders subjected to either an axial or a transverse magnetic field in a large range of field sweep rates, dBapp/dt. The behaviour of the superconductor was modelled in order to reproduce the main features of the field penetration curves by using a minimum number of free parameters suitable for both magnetic field orientations. The field penetration measurements were carried out on Pb-doped Bi-2223 tubes at 77 K by applying linearly increasing magnetic fields with a constant sweep rate ranging between 10 uT s[?]1 and 10 mT s[?]1 for both directions of the applied magnetic field. The experimental curves of the internal field versus the applied field, Bin(Bapp), show that, at a given sweep rate, the magnetic field for which the penetration occurs, Blim, is lower for the transverse configuration than for the axial configuration. A power law dependence with large exponent, n', is found between Blim and dBapp/dt. The values of n' are nearly the same for both configurations. We show that the main features of the curves Bin(Bapp) can be reproduced using a simple 2D model, based on the method of Brandt, involving a E(J) power law with an n-exponent and a field-dependent critical current density, Jc(B), (following the Kim model: Jc = Jc0(1+B/B1)[?]1). In particular, a linear relationship between the measured n'-exponents and the n-exponent of the E(J) power law is suggested by taking into account the field dependence of the critical current density. Differences between the axial and the transverse shielding properties can be simply attributed to demagnetizing fields. [less ▲]

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See detailMagnetic shielding properties of high-temperature superconducting tubes subjected to axial fields
Denis, Samuel ULg; Dusoulier, Laurent; Dirickx, Michel ULg et al

in Superconductor Science and Technology (2007), 20(3), 192-201

We have experimentally studied the magnetic shielding properties of a cylindrical shell of BiPbSrCaCuO subjected to low frequency AC axial magnetic fields. The magnetic response has been investigated as a ... [more ▼]

We have experimentally studied the magnetic shielding properties of a cylindrical shell of BiPbSrCaCuO subjected to low frequency AC axial magnetic fields. The magnetic response has been investigated as a function of the dimensions of the tube, the magnitude of the applied field and the frequency. These results are explained quantitatively by employing the method of Brandt ( 1998 Phys. Rev. B 58 6506) with a Jc( B) law appropriate for a polycrystalline material. Specifically, we observe that the applied field can sweep into the central region either through the thickness of the shield or through the opening ends, the latter mechanism being suppressed for long tubes. For the first time, we systematically detail the spatial variation of the shielding factor ( the ratio of the applied field over the internal magnetic field) along the axis of a high-temperature superconducting tube. The shielding factor is shown to be constant in a region around the centre of the tube, and to decrease as an exponential in the vicinity of the ends. This spatial dependence comes from the competition between two mechanisms of field penetration. The frequency dependence of the shielding factor is also discussed and shown to follow a power law arising from the finite creep exponent n. [less ▲]

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See detailMagnetic shielding properties of tubular bulk superconductors subjected to stray magnetic fields
Hogan, Kevin ULg; Fagnard, Jean-François ULg; Wera, Laurent ULg et al

Conference (2015, September 04)

Superconducting materials act as efficient magnetic shields thanks to their intrinsic magnetic properties. The vast majority of studies on superconducting shields has been conducted in homogeneous ... [more ▼]

Superconducting materials act as efficient magnetic shields thanks to their intrinsic magnetic properties. The vast majority of studies on superconducting shields has been conducted in homogeneous magnetic field configurations. Only few works have been done concerning inhomogeneous magnetic field configurations while those are representative of practical situations. Moreover, those configurations are non-trivial given the magnetic hysteretic behaviour of type-II superconductors. In the present work, we aim at investigating and understanding the magnetic response of a superconducting hollow cylinder made of Bi-2223 subjected to the magnetic stray field of various magnetic sources. Thanks to a bespoke 3D mapping system and a three-axis Hall probe, we measure the magnetic flux density distribution in the vicinity of the cylinder when the latter is subjected to those stray fields. All experiments are carried out in liquid nitrogen. Our experimental data allow us to apprehend the magnetic field penetration inside the superconductor in inhomogeneous field configurations and to compare those to results obtained with homogeneous fields. Then we compare our results to a finite element model of an infinite tube subjected to an inhomogeneous magnetic field in order to gather information on the magnetic field penetration and the current density distribution inside the superconductor. [less ▲]

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See detailMagnetic Shielding with Bulk High Temperature Superconductors: Factors Influencing the Magnetic Field Penetration in Hollow Cylinders
Fagnard, Jean-François ULg; Vanderheyden, Benoît ULg; Vanderbemden, Philippe ULg

in Muralidhar, Miryala (Ed.) Superconductivity: Recent Developments and New Production Technologies (2012)

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See detailMagnetic Shielding with Bulk High Temperature Superconductors: Improvement of the Shielded Volume in Hollow Cylinders
Wera, Laurent ULg; Fagnard, Jean-François ULg; Hogan, Kevin ULg et al

in Muralidhar, Miryala (Ed.) Superconductivity: Applications Today and Tomorrow (2016)

The superconducting HTS hollow cylinder has been one of the first geometries to demonstrate its utility as an efficient passive magnetic shield, and particularly for DC magnetic shielding. The shielding ... [more ▼]

The superconducting HTS hollow cylinder has been one of the first geometries to demonstrate its utility as an efficient passive magnetic shield, and particularly for DC magnetic shielding. The shielding performances can be characterized by two parameters: (i) the shielding factor SF, defined as the ratio between the applied magnetic induction Bapp and the magnetic induction inside the shield Bin and (ii) the threshold induction Blim for which the shielding factor becomes lower than a given level. The main drawback of the hollow cylinder geometry is that the shielding is only effective in the central region of the tube and decreases towards the tube extremities because of the field penetration through the open ends. In order to improve the performances at tube extremities and hence increase the shielded volume, the tube should be closed. This can be achieved by using a superconducting vessel or by closing one or both extremities with a cap. This chapter describes the experimental and the numerical analysis of the DC shielding performances of a Bi-2223 tube closed by a superconducting Bi-2223 cap, for an axial configuration. The first part is dedicated to the experimental study of two tubes of different lengths when they are closed at one extremity or closed at both extremities. We also study the effect of the gap size between the cap and the tube. In the second part, we use numerical simulations to highlight the possible improvements and to optimize the design. In particular we study the influence of the critical current density and of the thickness of the cap. [less ▲]

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See detailMagnetic shielding with YBCO coated conductors: influence of the geometry on its performances
Wera, Laurent ULg; Fagnard, Jean-François ULg; Levin, G. A. et al

in IEEE Transactions on Applied Superconductivity (2012), 23(3), 8200504

A superconducting magnetic shield can be built as a stack of several sections of milled 2G coated conductors. Each section consists of a closed loop where persistent currents can flow and provide a strong ... [more ▼]

A superconducting magnetic shield can be built as a stack of several sections of milled 2G coated conductors. Each section consists of a closed loop where persistent currents can flow and provide a strong attenuation of external dc magnetic fields. The purpose of the present work is to study experimentally several geometries of such magnetic shields made out of YBa2Cu3O7 (YBCO) coated conductors from SuperPower. Our aim is to investigate in detail the influence of the aspect ratio and the number of layers of the assembly on the magnetic shielding properties. In order to do so, the magnetic shield is subjected to an axial quasi-static (“dc”) magnetic field ramped slowly at a fixed sweep rate. A Hall probe is used to measure the local magnetic induction inside the assembly as a function of the appliedmagnetic induction. Results show that the shielding factor, SF, (defined as the ratio between the appliedmagnetic induction and the magnetic induction measured inside the shield) is improved for increasing aspect ratios of the global coated conductor assembly and that the threshold magnetic induction (defined for SF = 10) increases with the number of layers. Using a double layer of 18 sections at T = 77 K, dc magnetic fields up to 56 mT can be shielded by a factor larger than 10. Finally, the effect of an air gap of constant width between coated conductor sections is also characterized.(C) 2012 IEEE [less ▲]

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See detailMagnetic shielding with YBCO coated conductors: influence of the geometry on its performances.
Wera, Laurent ULg; Fagnard, Jean-François ULg; Levin, George et al

Poster (2012, October 10)

A superconducting magnetic screen can be built as a stack of several sections of milled 2G coated conductors. Each section consists of a closed loop where persistent currents can flow and provide a strong ... [more ▼]

A superconducting magnetic screen can be built as a stack of several sections of milled 2G coated conductors. Each section consists of a closed loop where persistent currents can flow and provide a strong attenuation of external dc magnetic fields. The purpose of the present work is to study experimentally several geometries of such magnetic screens made out of YBa2Cu3O7 (YBCO) coated conductors from SuperPower. Our aim is to investigate in details the influence of the aspect ratio and the number of layers of the assembly on the magnetic shielding properties. In order to do so, the magnetic screen is subjected to an axial quasi-static (“dc”) magnetic field ramped slowly a fixed sweep rates. A Hall probe is used to measure the local magnetic induction inside the assembly as a function of the applied magnetic induction. Results show that the threshold magnetic induction (above which magnetic shielding ceases) increases with the number of layers and that the shielding factor (defined as to ratio between the applied magnetic induction and the magnetic induction measured inside the screen) is improved for increasing aspect ratios of the global coated conductor assembly. Using a double layer of 18 sections at T = 77 K, dc magnetic fields up to 56 mT can be shielded by a factor larger than 10. The experimental results are compared to theoretical predictions for a perfect (type-I) magnetic shield with the same aspect ratio. Finally, the effect of an air gap of constant width between coated conductor sections is also characterized. [less ▲]

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See detailMagnetic solid-phase enzyme immunoassay for the detection of anti-glomerular basement membrane antibodies.
Druet, E.; Mahieu, P.; Foidart, Jean-Michel ULg et al

in Journal of Immunological Methods (1982), 48(2), 149-57

A new enzyme immunoassay has been developed for the demonstration of antiglomerular basement membrane antibodies. Magnetically responsive polyacrylamide-agarose beads (Magnogel) activated with ... [more ▼]

A new enzyme immunoassay has been developed for the demonstration of antiglomerular basement membrane antibodies. Magnetically responsive polyacrylamide-agarose beads (Magnogel) activated with glutaraldehyde were used to bind sonicated insoluble rat glomerular basement membranes. Both the collagenous and the non-collagenous moieties were demonstrated to be fixed on the beads. Sera from brown Norway rats with anti-glomerular basement membrane antibodies induced by HgCl2 injections were incubated with the beads. After washing, the fixed rat IgG were revealed using alkaline phosphatase labelled Fab fragments from anti-rat IgG sheep, IgGs. Comparison with a radioimmunoassay showed that results were reliable. This enzyme immunoassay has several advantages which may render this assay of considerable clinical usefulness. [less ▲]

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See detailMagnetic Stars
Ledoux, Paul ULg; Renson, Pierre ULg

in Annual Review of Astronomy and Astrophysics (1966), 4

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See detailMagnetic stimulation in multiple sclerosis ans peripheral neuropathies
MAERTENS DE NOORDHOUT, Alain ULg

in Pascual-Leone, Alvara; Davey, N. J.; Rothwell, John (Eds.) et al Handbook of transcranial Magnetic Stimulation (2002)

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See detailMagnetic Stimulation of the Motor Cortex in Cervical Spondylosis
Maertens De Noordhout, Alain ULg; Remacle, J. M.; PEPIN, Jean-Louis ULg et al

in Neurology (1991), 41(1), 75-80

We report a new technique of transcranial magnetic stimulation of the motor cortex to measure conduction within central motor pathways of 67 patients with cervical spondylosis or disk herniation. There ... [more ▼]

We report a new technique of transcranial magnetic stimulation of the motor cortex to measure conduction within central motor pathways of 67 patients with cervical spondylosis or disk herniation. There were upper motor neuron signs in 34 patients (51%) and x-ray evidence of cervical cord compression in 44 (66%). Muscle action potentials (MAPs) to cortical stimulation were abnormal in 84% of patients with, and 22% of those without, radiologic signs of cervical cord compression. Median nerve somatosensory evoked potentials were altered in only 25% of patients. The frequency of MAP alterations correlated with upper motor neuron signs. In 5 (11%) of the 44 patients with x-ray evidence of cervical cord compression, subclinical cord compression was disclosed by cortical stimulation. In 10 patients restudied 3 months after surgical decompression, normalization of central motor conduction time did not occur, indicating permanent damage to the cervical cord. [less ▲]

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See detailMagnetic stimulation of the motor cortex in cervical spondylotic myelopathy
MAERTENS DE NOORDHOUT, Alain ULg

in Lissens, M. A. (Ed.) Clinical Applications of magnetic transcranial stimulation (1992)

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See detailMagnetic stimulation of the motor cortex in early multiple sclerosis
MAERTENS DE NOORDHOUT, Alain ULg; Charlier, Marianne; Delwaide, Paul ULg

in Gonsette, R. E.; Delmotte, P. (Eds.) Recent advances in multiple sclerosis therapy (1989)

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See detailMagnetic storm effects on the tropical ultraviolet airglow
Gérard, Jean-Claude ULg; Anderson, D. N.; Matsushita, S.

in Journal of Geophysical Research (1977), 82

Ogo 4 measurements of the UV equatorial airglow made during a period which included a major magnetic storm are analyzed and used as an indicator of wind direction and velocity as well as ExB drift ... [more ▼]

Ogo 4 measurements of the UV equatorial airglow made during a period which included a major magnetic storm are analyzed and used as an indicator of wind direction and velocity as well as ExB drift magnitude and phase. Some features of the airglow intensity and distribution are explained in terms of storm-induced changes in vertical drift velocity, neutral composition, or both. The observations are shown to be consistent with an eastward neutral wind that transports ionization from the Southern to the Northern Hemisphere while raising the F layer in the South and lowering it in the North. Theoretical modeling of the low-latitude F-region ionosphere indicates that an eastward wind with velocity approaching 300 m/s at 2100 LT can qualitatively produce the observed hemispheric asymmetries in airglow emission rates. [less ▲]

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See detailMagnetic structures of U2Rh2Sn and U2Ni2In
Nakotte, Heinz; Purwanto, A.; Robinson, R. A. et al

Poster (1995, April)

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See detailMagnetic susceptibility and cyclic arrangements from the late Devonian (Frasnian) Hull platform, Canning Basin, Australia.
Da Silva, Anne-Christine ULg; George, Annette; Chow, Nancy

in Travaux de Geophysiques (2010), XXXIX

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See detailMagnetic susceptibility and electron magnetic resonance study of monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3
Thaljaoui, R.; Pękała, K.; Pękała, M. et al

in Journal of Alloys and Compounds (2013), 580(0), 137-142

The monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3 (x = 0.05–0.2) are characterized using the complementary magnetic susceptibility and electron resonance methods. In paramagnetic phase the ... [more ▼]

The monovalent potassium doped manganites Pr0.6Sr0.4−xKxMnO3 (x = 0.05–0.2) are characterized using the complementary magnetic susceptibility and electron resonance methods. In paramagnetic phase the temperature variations of the inverse magnetic susceptibility and the inverse intensity of resonance signal obey the Curie–Weiss law. A similarity in temperature variation of resonance signal width and the adiabatic polaron conductivity points to the polaron mechanism controlling the resonance linewidth. The low temperature limit of the pure paramagnetic phase is determined from the electron resonance spectra revealing the mixed phase spread down to the Curie temperature. [less ▲]

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