Zemma, E., and J. Luzuriaga. "Turbulent Flow Around an Oscillating Body in Superfluid Helium: Dissipation Characteristics of the Nonlinear Regime." Journal of Low Temperature Physics 172, no. 3-4 (2013): 256–265.
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.
|
Marconi V. I., H. Pastoriza, and D. Domínguez. "Transverse voltage in disordered Josephson junction arrays with diagonal bias." Journal of Low Temperature Physics 135 (2004): 135–138.
Abstract: We study numerically the effect of disorder in the transport properties of square Josephson junction arrays with a dc current applied in the diagonal direction ([11] direction). We obtain a finite transverse voltage in this case when we consider the presence of disorder in the critical currents of the junctions. We show that this behavior is in good agreement with previous experimental, results in square arrays with a diagonal current drive.
|
Guimpel, J., M. E. de la Cruz, F. de la Cruz, H. J. Fink, O. Laborde, and J. C. Villegier. "Size dependence of the Superconducting critical temperature and fields of Nb/Al multilayers." Journal of Low Temperature Physics 63, no. 1-2 (1986): 151–165.
Abstract: The critical temperatureT cof Nb/Al multilayers decreases as the total sample thicknessd Tis decreased while the thickness of each Nb and Al layer is kept constant. To understand this behavior, models based on the proximity effect and on weak two-dimensional (2D) localization are employed. The latter uses a characteristic length, the thermal diffusion length, in relation tod Tto obtain 2D behavior and leads to a reasonable explanation ofT c(d T). It is also found that the slope atT c(d T) of the critical magnetic field perpendicular to the layers is independent ofd Twhen the Nb and Al layer thicknesses are kept constant. The angular dependence of the critical field is also measured.
|
Trovarelli, O., J. G. Sereni, and J. P. Kappler. "Role of Ce sublattices in the thermal and magnetic properties of Ce7X3 (X=Ni, Ru, Rh, Ir, Pd, and Pt) compounds." Journal of Low Temperature Physics 108, no. 1-2 (1997): 53–85.
Abstract: 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.
|
Zemma, E., M. Tsubota, and J. Luzuriaga. "Possible visualization of a superfluid vortex loop attached to an oscillating Beam." Journal of Low Temperature Physics 179, no. 5 (2015): 310–319.
Abstract: Visualization using tracer particles is a relatively new tool available for the study of superfluid turbulence and flow, which is applied here to oscillating objects submerged in the liquid. We report observations of a structure seen in videos taken from outside a cryostat filled with superfluid helium at 2 K, which is possibly a vortex loop attached to an oscillator. The feature, which has the shape of an incomplete arch, is visualized due to the presence of solid H2 tracer particles and is attached to a beam oscillating at 38 Hz in the liquid. It has been recorded in videos taken at 240 frames per second, fast enough to take ∼6 images per period. This makes it possible to follow the structure, and to see that it is not rigid. It moves with respect to the oscillator, and its displacement is in phase with the velocity of the moving beam. Analyzing the motion, we come to the conclusion that we may be observing a superfluid vortex attached to the beam and decorated by the hydrogen particles. An alternative model, considering a solid hydrogen filament, has also been analyzed, but the observed phase between the movement of the beam and the filamentary structure is better explained by the superfluid vortex hypothesis.
|
Cruz, F. de la, Y. Fasano, M. D. Seta, M. Menghini, and H. Pastoriza. "Plastic and Elastic Symmetry Transformations Induced in the Vortex Lattice of Anisotropic and Layered Superconductors." Journal of Low Temperature Physics 135 (2004): 99–110.
Abstract: 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$_2$.
|
Sereni, J. G. "Peculiar thermal features of Ce-systems around their critical points." JOURNAL OF LOW TEMPERATURE PHYSICS 147, no. 3-4 (2007): 179–197.
Abstract: 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.
|
Schmoranzer, D., M. J. Jackson, and J. Luzuriaga. "On the Non-linear Damping of Mechanical Oscillators in Flows of 4He." Journal of Low Temperature Physics 175, no. 1 (2014): 97–103.
Abstract: In the studies of both classical and quantum turbulence, significant attention is devoted to the investigation of the behavior of various submerged resonators. Upon entering the turbulent regime, the oscillators start to experience a significant drag force, which varies non-linearly with velocity. We present an empirical way of modeling such systems, and calculate the expected resonant response of such oscillators near the fundamental frequency as a function of the applied driving force. We apply the model to the crossover from linear to non-linear drag forces and compare with previous models as well as selected experimental data on the transition to turbulence in oscillatory flow of 4He.
|
Zemma, E., and J. Luzuriaga. "Measurements of Turbulence Onset and Dissipation in Superfluid Helium with a Silicon Double Paddle Oscillator." Journal of Low Temperature Physics 166, no. 3-4 (2012): 171–181.
Abstract: 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.
|
Luzuriaga, J. "Measurements in the laminar and turbulent regime of superfluid4He by means of an oscillating sphere." Journal of Low Temperature Physics 108, no. 3-4 (1997): 267–277.
Abstract: The translational oscillations of a sphere in liquid helium have been measured as a way of studying superfluid turbulence. Experiments were carried out in the laminar flow regime for reference purposes, and good agreement found between measured and calculated quantities. In the turbulent region, the dissipation is found to be proportional to the square of the velocity of the sphere, as found previously by other workers. For high vibration amplitudes there is an increase in the hydrodynamic mass. This seems to scale with the superfluid fraction in a way that strongly suggests that the superfluid component plays an important role in the turbulent regime.
|
