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Zemma, E.; Luzuriaga, J. |
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Title |
Turbulent Flow Around an Oscillating Body in Superfluid Helium: Dissipation Characteristics of the Nonlinear Regime |
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2013 |
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Journal of Low Temperature Physics |
Abbreviated Journal |
J. Low Temp. Phys. |
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172 |
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3-4 |
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256-265 |
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Keywords |
Quantum fluids; Turbulence; Superfluid helium; Nonlinear oscillator; Vibrating paddle; Critical velocity |
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Abstract |
By examining the resonance curves of an oscillator submerged in superfluid liquid helium, it is found that their shape is affected by two distinct dissipation regimes when the amplitude is large enough to generate turbulence in the liquid. In a resonance curve, the central part close to resonance, may be in a turbulent regime, but the response is of much lower amplitude away from the resonance frequency, so that the oscillation can still be in the linear regime for frequencies not exactly at resonance. This introduces an ambiguity in estimating the inverse quality factor Q −1 of the oscillator. By analyzing experimental data we consider a way of matching the two ways of estimating Q −1 and use the information to evaluate the frictional force as a function of velocity in a silicon paddle oscillator generating turbulence in the superfluid. |
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Springer US |
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0022-2291 |
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BT @ pedrazp @ |
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662 |
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Author |
Zemma, E.; Luzuriaga, J. |
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Title |
Measurements of Turbulence Onset and Dissipation in Superfluid Helium with a Silicon Double Paddle Oscillator |
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Journal Article |
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Year |
2012 |
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Journal of Low Temperature Physics |
Abbreviated Journal |
J. Low Temp. Phys. |
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166 |
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3-4 |
Pages |
171-181 |
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We have studied experimentally the response of a silicon single crystal double paddle oscillator submerged in superfluid helium from the lambda point to 1.55 K. Measuring the resonance frequency and dissipation on three modes of this high Q system allows us to study the dissipation at the onset of turbulence in the flow around the paddle. The critical velocity V c for turbulence onset decreases with temperature. If we use the density of the normal component of the superfluid to obtain a Reynolds number Re associated with V c we find a value which is largely temperature independent. This result is different from the behavior previously found by other authors below 1 K, where the quantized vorticity (extrinsic nucleation) is observed at velocities more than an order of magnitude greater. In our temperature range, we conclude that the transition is governed by the normal fraction acting as a classical fluid. The laminar regime shows a dissipation that is proportional to the viscous drag calculated by well known formulas for an object oscillating in a liquid. We also find a decrease in resonance frequency in the turbulent regime which is clearly observed but hard to reproduce from run to run. |
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1573-7357 |
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BT @ hernan @ |
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648 |
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Trovarelli, O.; Sereni, J.G.; Kappler, J.P. |
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Title |
Role of Ce sublattices in the thermal and magnetic properties of Ce7X3 (X=Ni, Ru, Rh, Ir, Pd, and Pt) compounds |
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Journal Article |
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Year |
1997 |
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Journal of Low Temperature Physics |
Abbreviated Journal |
J. Low. Temp. Phys. |
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108 |
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1-2 |
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53-85 |
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The role of the Ce sublattices in the thermal and magnetic properties of the Ce7X3 (X = Ni, Ru, Rh, Ir, Pd, and Pt) family of compounds is studied by means of ac and dc magnetic susceptibility, mngnetization and mainly specific-heat experiments in applied magnetic field. The experimental data show that in these compounds there is coexistence of magnetic order, heavy-fermion and intermediate-valence behavior, which is interpreted in terms of the contribution of the three different sublattices present in the crystalline structure of Th7Fe3-type (denoted by 1Ce(I), 3Ce(II) and 3Ce(III)). From the available volume of the Ce-III atoms in their crystallographic environment it is found that sublattice Ce-III has an intermediate-valence behavior, whereas from entropic considerations sublattices Ce-I and Ce-II are identified as responsible for the magnetic order or heavy-fermion behavior, depending on the Ce-ligand electronic structure. This systematics evidences a clear correlation between the thermal and magnetic properties of these compounds and the position of the respective Ce-ligands in the periodic table, through the particular sensitivity of Ce to the environmental conditions. |
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0022-2291 |
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ISI:A1997XK19200004 |
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BT @ hernan @ |
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92 |
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Cruz, F. de la; Fasano, Y.; Seta, M.D.; Menghini, M.; Pastoriza, H. |
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Title |
Plastic and Elastic Symmetry Transformations Induced in the Vortex Lattice of Anisotropic and Layered Superconductors |
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Journal Article |
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2004 |
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Journal of Low Temperature Physics |
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135 |
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99-110 |
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We make a comparative analysis of the response of the three-dimensional vortex lattice in Bi$2$Sr$2$CaCu$2Ο8$ and NbSe$2$ to the presence of square arrays of pinning sites localized at one extremity of the vortex crystals. The absence of the hexagonal to square symmetry transformation and the induction of a distorted hexagonal symmetry in the vortex lattice of NbSe$2$ contrast to the observed symmetry change in Bi$2$Sr$2$CaCu$2Ο8$. The dissimilar response in both cases is explained taking into account the vortex structure solidification mechanisms in both materials: The plastic response in the case of the layered material Bi$2$Sr$2$CaCu$2Ο8$ is suggested to be a result of the simultaneity of solidification and coupling of bidimensional pancake vortices whereas a viscous solidification is the responsible for the three-dimensional elastic response in NbSe$_2$. |
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BT @ hernan @ delacruz04 |
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15 |
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Author |
Hernandez,A.; Ares,O.; Hart, C.; Domínguez,D.; Pastoriza,H.; Butera, A. |
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Title |
Dissipation in mesoscopic superconductors with ac magnetic fields |
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Journal Article |
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Year |
2004 |
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Journal of Low Temperature Physics |
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Volume |
135 |
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119-122 |
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The response of mesoscopic superconductors to an ac magnetic field is investigated both experimentally
and with numerical simulations. We study small square samples with dimensions of the order of the penetration depth.
We obtain the ac susceptibitity $\chi=\chi'+\chi“$ at microwave frequencies as a function of the dc magnetic field
$H{dc}$. We find that the dissipation, given by $\chi”$, has a non monotonous behavior in mesoscopic samples.
In the numerical simulations we obtain that the dissipation increases before the penetration of vortices and
then it decreases abruptly after vortices have entered, the sample. This is verified experimentally, where we
find that $\chi"$ has strong oscillations as a function of $H{dc}$ in small squares of Pb |
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BT @ hernan @ hernandez04 |
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24 |
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Author |
Sereni, J.G. |
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Title |
Peculiar thermal features of Ce-systems around their critical points |
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2007 |
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JOURNAL OF LOW TEMPERATURE PHYSICS |
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147 |
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3-4 |
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179-197 |
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Some non-predicted thermal behavior observed in various Ce-lattice compounds close to their critical points are presented. From a comparison between phase diagrams driven by doping (x) and pressure, a pre-critical region (x* < x < x(cr)) is identified in the former group. Some systematic behaviors, observed in the specific heat (C-m/T) and the entropy gain, are recognized as characteristic features of that region. Different measured temperature dependencies of C-m/T are compared, detecting that the onset of the non-Fermi-liquid behavior occurs much closer to x* than x(cr). In a detailed analysis of the evolution of the thermal dependence within the pre-critical region, a further change in the T dependence is frequently observed before to reach the critical point. A generalized power law function is proposed to compare different systems, which allows to identify a low temperature C-m/T(T) anomaly that only involves about 0.01 x R ln 2 of entropy. |
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0022-2291 |
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ISI:000245133000008 |
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BT @ hernan @ |
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52 |
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Guimpel, J.; Haberkorn, N.; Sirena, M.; Steren, L.B.; Saldarriaga, W.; Baca, E.; Gomez, M.E. |
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Title |
Interface effects in perovskite superlattices |
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2004 |
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JOURNAL OF LOW TEMPERATURE PHYSICS |
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135 |
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1-2 |
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115-118 |
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The effect of interface disorder in perovskite superlattices, either with the substrate or between layers dominates the physics of the material, even when the lattice parameter of the component materials differs in less than 1%. Unexpected behavior emerges, like exchange bias in a system where no antiferromagnetic material has been included in the superlattice design. |
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0022-2291 |
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ISI:000189139000012 |
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BT @ hernan @ |
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166 |
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