| Records |
Author  |
Zemma, E.; Tsubota, M.; Luzuriaga, J. |
| Title |
Possible visualization of a superfluid vortex loop attached to an oscillating Beam |
Type |
Journal Article |
| Year |
2015 |
Publication |
Journal of Low Temperature Physics |
Abbreviated Journal |
J. Low Temp. Phys. |
| Volume |
179 |
Issue |
5 |
Pages |
310-319 |
| Keywords |
Quantum fluids; Superfluid helium; Flow visualization; Vortex loops |
| 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. |
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BT @ pedrazp @ |
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734 |
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| Author |
Zemma, E.; Luzuriaga, J. |
| Title |
Measurements of Turbulence Onset and Dissipation in Superfluid Helium with a Silicon Double Paddle Oscillator |
Type |
Journal Article |
| Year |
2012 |
Publication |
Journal of Low Temperature Physics |
Abbreviated Journal |
J. Low Temp. Phys. |
| Volume |
166 |
Issue |
3-4 |
Pages |
171-181 |
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| 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. |
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1573-7357 |
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BT @ hernan @ |
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648 |
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| Author |
Zemma, E.; Luzuriaga, J. |
| Title |
Anomalous Trajectories of H2 Solid Particles Observed Near a Sphere Oscillating in Superfluid Turbulent 4He |
Type |
Journal Article |
| Year |
2013 |
Publication |
Journal of Low Temperature Physics |
Abbreviated Journal |
J. Low Temp. Phys. |
| Volume |
173 |
Issue |
1-2 |
Pages |
71-79 |
| Keywords |
Quantum fluids; Turbulence; Superfluid helium; Flow visualization; Oscillating sphere |
| Abstract |
Using a relatively low cost apparatus, consisting of a glass dewar and a digital camera capable of taking images at 240 frames per second we have observed trajectories of frozen H2 particles which follow the flow of liquid helium below 2 K, around a sphere oscillating at 38 Hz. In some of the images the motion is compatible with laminar flow, while at high amplitudes, where we can reach Reynolds numbers of a few thousand in the normal component, the flow is clearly turbulent. In some of the videos taken we find particles being suddenly accelerated to several times the velocity of the oscillating sphere. |
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Springer US |
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0022-2291 |
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BT @ pedrazp @ |
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661 |
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| Author |
Zemma, E.; Luzuriaga, J. |
| Title |
Turbulent Flow Around an Oscillating Body in Superfluid Helium: Dissipation Characteristics of the Nonlinear Regime |
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Journal Article |
| Year |
2013 |
Publication |
Journal of Low Temperature Physics |
Abbreviated Journal |
J. Low Temp. Phys. |
| Volume |
172 |
Issue |
3-4 |
Pages |
256-265 |
| Keywords |
Quantum fluids; Turbulence; Superfluid helium; Nonlinear oscillator; Vibrating paddle; Critical velocity |
| 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 |
Trovarelli, O.; Sereni, J.G.; Kappler, J.P. |
| 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 |
| Year |
1997 |
Publication |
Journal of Low Temperature Physics |
Abbreviated Journal |
J. Low. Temp. Phys. |
| Volume |
108 |
Issue |
1-2 |
Pages |
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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no |
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BT @ hernan @ |
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92 |
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Shalóm, D. E.; Pastoriza, H. |
| Title |
Experimental Method to Measure Anisotropic Transport in 2D Superconductors |
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Journal Article |
| Year |
2004 |
Publication |
Journal of Low Temperature Physics |
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135 |
Issue |
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Pages |
153-156 |
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A two-coil kinetic inductance technique for measuring anisotropic response in two-dimensional (2D) superconductors is presented. Serpentine-shaped coils are lithographically patterned directly on top of the sample, separated by isolation layers. The drive and receive coils are positioned in a way that enhances signal from longitudinal currents and reduces transversal ones, maximizing the ratio. Anisotropic transport can be directly measured with this technique, even when anisotropy is induced by the transport current. |
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BT @ hernan @ shalom04a |
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43 |
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Sereni, J.G.; Huber, J.G.; Luengo, C.A.; Maple, M.B. |
| Title |
Calorimetric study of the magnetization of Ce impurities in superconducting Th-Y and Th-Sc alloys |
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Journal Article |
| Year |
1978 |
Publication |
Journal of Low Temperature Physics |
Abbreviated Journal |
J. Low Temp. Phys. |
| Volume |
30 |
Issue |
5-6 |
Pages |
729-737 |
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Specific heat measurements are reported in detail for the Ce impurity in the superconducting matrix systems Th65Sc35Ce, Th80Y20Ce, and Th65Y35Ce. The variation of the specific heat jump DeltaC at the superconducting transition temperature T c is indicative of the magnetic nature of an impurity. For Th65Y35Ce a departure is found from the BCS law of corresponding states predicted for a nonmagnetic impurity. This departure is correlated with that observed for (La, Th)Ce systems and related to DeltaT c/n (initial slope of T c vs. n) and Ce effective size (implied by lattice parameter data). |
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0022-2291 |
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ISI:A1978EW47300012 |
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no |
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BT @ hernan @ |
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140 |
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| Author |
Sereni, J.G. |
| Title |
Peculiar thermal features of Ce-systems around their critical points |
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Journal Article |
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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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no |
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BT @ hernan @ |
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52 |
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| Author |
Sereni, J.G. |
| Title |
Entropy Bottlenecks at T->0 in Ce-Lattice and Related Compounds |
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Journal Article |
| Year |
2015 |
Publication |
Journal of Low Temperature Physics |
Abbreviated Journal |
J. Low Temp. Phys. |
| Volume |
179 |
Issue |
1-2 |
Pages |
126-137 |
| Keywords |
Heavy fermions; Specific heat anomalies; Entropy |
| Abstract |
A number of specific heat Cm anomalies are reported in Ce- and Yb-lattice compounds around 1 K which cannot be associated to usual phase transitions despite of their robust magnetic moments. Instead of a Cm(T) jump, these anomalies show coincident morphology: (i) a significant tail in Cm/T , with similar power law decay above their maxima ( T>Tm ), (ii) whereas a Cm(T2) dependence is observed below Tm . (iii) The comparison of their respective entropy gain Sm(T) indicates that ≈0.7R ln2 is condensed within the T>Tm tail, in coincidence with an exemplary spin-ice compound. Such amount of entropy arises from a significant increase of the density of low energy excitations, reflected in a divergent Cm(T>Tm)/T dependence. (iv) Many of their lattice structures present conditions for magnetic frustration. The origin of these anomalies can be attributed to an interplay between the divergent density of magnetic excitations at T→0 and the limited amount of degrees of freedom: Sm = R ln2 for a doublet-ground state. Due to this “entropy bottleneck,†the paramagnetic minimum of energy blurs out and the system slides into an alternative minimum through a continuous transition. A relevant observation in these very heavy fermion systems is the possible existence of an upper limit for Cm/TLimT→0 ≈7 J/mol K 2 observed in four Yb- and Pr-based compounds. |
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Springer US |
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0022-2291 |
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BT @ pedrazp @ |
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709 |
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| Author |
Sereni, J.G. |
| Title |
Entropy Constraints in the Ground State Formation of Magnetically Frustrated Systems |
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Journal Article |
| Year |
2017 |
Publication |
Journal of Low Temperature Physics |
Abbreviated Journal |
J. Low Temp. Phys. |
| Volume |
190 |
Issue |
1-2 |
Pages |
1-19 |
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| Abstract |
A systematic modification of the entropy trajectory (Sm(T)) is observed at very low temperature in magnetically frustrated systems as a consequence of the constraint (Sm≥0) imposed by the Nernst postulate. The lack of magnetic order allows to explore and compare new thermodynamic properties by tracing the specific heat (Cm) behavior down to the sub-Kelvin range. Some of the most relevant findings are: (i) a common Cm/T|T→0≈7 J/mol K2 ‘plateau’ in at least five Yb-based very-heavy-fermions (VHF) compounds; (ii) quantitative and qualitative differences between VHF and standard non-Fermi-liquids; (iii) entropy bottlenecks governing the change of Sm(T) trajectories in a continuous transition into alternative ground states. A comparative analysis of Sm(T→0) dependencies is performed in compounds suitable for adiabatic demagnetization processes according to their ∂2Sm/∂T2 derivatives. |
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BT @ pedrazp @ |
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