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Luzuriaga, J. |
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Title |
Sphere on a vibrating reed for measurements of turbulence in superfluid helium |
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2000 |
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Journal of Alloys and Compounds |
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J Alloys Compd |
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265-268 |
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Cantilever beams; Computational methods; Laminar flow; Oscillators (electronic); Phase transitions; Turbulent flow; Vibrations (mechanical); Oscillating spheres; Spherical geometries; Vibrating reeds; Superfluid helium |
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A modification of the vibrating reed, in which a massive sphere is made to oscillate at the end of a cantilevered beam, has been used for measurements in superfluid helium. The apparatus operates in the same way as a conventional vibrating reed with capacitive detection and drive. However, when operating submerged in the liquid, the frequency changes give information on the superfluid fraction, and the dissipation can be used to obtain information on the change of liquid flow, from laminar to turbulent. The spherical geometry allows an exact calculation of all parameters in the laminar regime, so departures due to the turbulence can be better quantified. The method has been found to work well in practice, and some measurements on the turbulent regime in the superfluid are presented. |
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Elsevier Sequoia SA |
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Buenos Aires, Argent |
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12th International Conference on Internal Friction and Ultrasonic Attenuation in Solids (ICIFUAS-12) |
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310 |
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1-2 |
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09258388 (ISSN) |
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Conference code: 57483; Export Date: 28 April 2009; Source: Scopus; CODEN: JALCE; doi: 10.1016/S0925-8388(00)00962-2; Language of Original Document: English; Correspondence Address: Luzuriaga, Javier; Centro Atomico Bariloche Bariloche, Argentina; Sponsors: ABDUS SALAM International Centre for Theoretical Physics; Centre for Industrial Research (CINI); Comision Nacional de Actividades Espaciales (CONAE) |
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478 |
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André, M-O.; Polichetti, M.; Pastoriza, H.; Kes, P. H. |
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Title |
Vortex dynamics in 2H-NbSe$_2$ containing a periodic channel structure |
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Journal Article |
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2000 |
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Physica C |
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338 |
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179-188 |
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We have measured the resistivity and magnetic AC susceptibility of 2H-NbSe single crystals containing alternating 2 stripes of irradiated and non-irradiated regions of columnar defects created by heavy-ion bombardment. Without applied magnetic field, the sample undergoes a double-step transition into the superconducting state, each step corresponding to the transitions in the irradiated and non-irradiated regions, respectively. For fields smaller than half of the matching field and upon increasing the temperature, the onset of flux motion in the non-irradiated channels occurs, when the applied stress due to the electrical current equals the shear stress at the channel edges, while depinning in the irradiated stripes occurs at higher temperature. The weak amplitude dependence of the shear process suggests that it takes place at the melting transition. We observed only a single-step transition at DC magnetic fields larger than half the matching field, because pinning by the columnar defects in the irradiated stripes is much less effective, and consequently the shear stress at the channel edges is strongly reduced. The comparison between the shear stress deduced from I curves and the theoretical value $?max = AC66$ yields a value for the constant Α, which is in good agreement with theoretical predictions. |
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BT @ hernan @ andre99 |
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2 |
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Marconi, V. I.; Candia, S.; Balenzuela, P.; Pastoriza, H.; Domínguez, D.; Martinoli, P. |
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Title |
Orientational pinning and transverse voltage: Simulations and experiments in square Josephson junction arrays |
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2000 |
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Phys. Rev. B |
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62 |
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6 |
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4096-4104 |
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We study the dependence of the transport properties of square Josephson Junctions arrays with the direction of the applied dc current, both experimentally and numerically. We present computational simulations of current-voltage curves at finite temperatures for a single vortex in an array of $L\times L$ junctions ($Ha^2/?_0=f=1/L^2$), and experimental measurements in $100\times1000$ arrays under a low magnetic field corresponding to $f\approx0.02$. We find that the transverse voltage vanishes only in the directions of maximum symmetry of the square lattice: the [10] and [01] direction (parallel bias) and the [11] direction (diagonal bias). For orientations different than the symmetry directions, we find a finite transverse voltage which depends strongly on the angle φ of the current. We find that vortex motion is pinned in the [10] direction ($?=0$), meaning that the voltage response is insensitive to small changes in the orientation of the current near $?=0$. We call this phenomenon orientational pinning. This leads to a finite transverse critical current for a bias at $?=0$ and to a transverse voltage for a bias at $?\not=0$. On the other hand, for diagonal bias in the [11] direction the behavior is highly unstable against small variations of φ, leading to a rapid change from zero transverse voltage to a large transverse voltage within a few degrees. This last behavior is in good agreement with our measurements in arrays with a quasi-diagonal current drive. |
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BT @ hernan @ marconi00 |
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26 |
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Pastoriza, H.; Candia, S.; Nieva, G. |
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Title |
Anisotropic vortex dynamics in twined YBaCuO single crystals |
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2000 |
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Physica B |
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284-288 |
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2 |
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763-764 |
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Rotating continuously the applied vortex force and measuring the vortex velocity vector, we were able to directly determine the role of twin boundaries in the vortex dynamics in YBa$2$Cu$3Ο_7$ single crystals with unidirectional twins. We show the different effect of these correlated pinning defects into the various vortex phases. In the entangled vortex liquid state, we observe a linear response but with an anisotropic viscosity. On the other hand, an anomalous guided motion by twin planes is found in the vortex solid. |
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BT @ hernan @ pastoriza00 |
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39 |
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Author |
Herbsommer, Juan A. |
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Title |
Dinámica y estática de vórtices en superconductores de alta temperatura crítica con defectos correlacionados |
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Book Whole |
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2000 |
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Instituto Balseiro |
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Ph.D. thesis |
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328 |
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Pedrazzini, P.; Schmerber, G.; Berisso, M.G.; Kappler, J.P.; Sereni, J.G. |
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Magnetic and superconducting properties of A(7)B(3) compounds (A = Th or La and B=Ni, Co, Fe or Pd, Rh, Ru) |
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2000 |
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PHYSICA C |
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336 |
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1-2 |
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10-18 |
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High-temperature magnetization, low temperature specific heat, and ac-susceptibility measurements on Th7X3 (X = Ni, Co, and Fe) and La(7)Z(3) (Z = Pd, Rh, and Ru) superconductors are presented. The magnetic behaviour of the Th7X3 group has the characteristics of Pauli paramagnets. The La(7)Z(3) group also shows Pauli paramagnetism for Z = Pd and Ru, and signs of spin fluctuations for La7Rh3. Specific heat (C-p) measurements indicate a conventional BCS behaviour for La7Pd3 and La7Rh3, like that of the previously measured Th7X3 superconductors. in the case of La7Ru3, the reduced specific heat jump at the transition, the anomalous temperature dependence of C-p under magnetic field and a large upper critical field slope are discussed. (C) 2000 Elsevier Science B.V. All rights reserved. |
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0921-4534 |
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ISI:000088047500002 |
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BT @ hernan @ |
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78 |
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Author |
Sereni, J.G. |
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Title |
Evanescence of magnetic transitions in Ce systems |
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2000 |
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Physica B – Condensed Matter |
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Physica B |
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281-282 |
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337-339 |
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Three types of magnetic phase diagrams can be identified in Ce systems: (I) with ordering temperature T-ord --> 0 continuously, followed by a narrow non-Fermi-liquid (NFL) region, (II) with T-ord vanishing at finite temperature, followed by an extended NFL region, and (III) where the degrees of freedom condensed into the ordered phase decreases, without a concomitant decrease of T-ord. Intrinsic differences are found in the way that the degrees of freedom condense at T-ord and from the rising of the specific heat tails above T-ord. (C) 2000 Elsevier Science B.V. All rights reserved. |
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0921-4526 |
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ISI:000086570200141 |
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BT @ hernan @ |
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79 |
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Silhanek, K.; Guimpel, J.; Civale, L.; Lanza, H.; Levy, P. |
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Thickness effects on the pinning by columnar defects |
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2000 |
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PHYSICA C |
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341 |
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1217-1218 |
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We compare the angular dependence of the pinning of equivalent columnar defects in GdBa2Cu2O7 thin films and a thicker YBa2Cu3O7 single crystal. The tracks' related enhancement of the critical currents is much smaller for the case of the thin films. We interpret this thickness dependence as resulting from a competition between the pinning of the correlated structures, related to total sample thickness, and surface boundary conditions, which force the vortices to depin from the columnar defects near the sample surface. |
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0921-4534 |
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ISI:000165855700208 |
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BT @ hernan @ |
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175 |
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Sirena, M.; Steren, L.; Guimpel, J. |
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Thickness dependence of the properties of La0.6Sr0.4MnO3 thin films |
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2000 |
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Thin Solid Films |
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373 |
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1-2 |
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102-106 |
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We have studied the thickness dependence of the transport and magnetic properties of strongly textured La0.6Sr0.4MnO3 thin films grown on MgO and SrTiO3, for thickness between 5 and 500 nm. While the resistivity and the magnetoresistance are strongly affected, the magnetization is only moderately changed. The effect on the metal-insulator transition, the low field magnetoresistance and carrier localization is dependent on the substrate, evidencing the effect of the induced defects and strains. (C) 2000 Elsevier Science S.A. All rights reserved. |
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0040-6090 |
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ISI:000090045900024 |
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176 |
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Steren, L.B.; Sirena, M.; Guimpel, J. |
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Substrate effect on the magnetic behavior of manganite films |
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2000 |
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JOURNAL OF APPLIED PHYSICS |
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87 |
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9 |
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6755-6757 |
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The film thickness (t) dependence of the magnetic properties of La0.6Sr0.4MnO3 (LSMO) films grown on (001) MgO and (001) SrTiO3 substrates has been studied. Hysteresis loops measured at low temperature show a smooth increase of the retentivity accompanied by a decrease of the coercitive field as the film thickness increases. The increase of coercitivity with decreasing t can be interpreted in terms of a change in the domain structure of the films mainly due to an augmentation of domain pinning defects. The magnetic anisotropy has been measured using ferromagnetic resonance (FMR). A volume (VA) and a surface (SA) anisotropy contribution have been deduced from FMR angular dependence studies for both series of samples. In the LSMO films grown on MgO a VA component that corresponds to an easy-axis perpendicular to the plane of the films has been found while in contrast, the LSMO films grown on SrTiO3 present an easy-plane anisotropy. The SA is positive for both series favoring a perpendicular magnetic anisotropy. The measured magnetic anisotropy has been assigned to substrate-induced effects. (C) 2000 American Institute of Physics. [S0021-8979(00)55708-9]. |
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0021-8979 |
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ISI:000086728800281 |
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