Francesco Celani

Temperature coefficient of resistivity at compositions approaching PdH

Abstract Measurements have been made of the temperature coefficient of resistivity, λ , versus hydrogen concentration, H/Pd, at very high concentrations in the Pd–H system. Unusually high hydrogen compositions were achieved using an electrochemical loading procedure which allowed stable Pd–H systems to be obtained. It is well known that increasing the H/Pd concentrations leads to three different phases ( α , α + β , β ), respectively, in the Pd–H system; the β phase is thought to end in an asymptotic limit. Possible evidence that a new phase ( γ ) exists, bordering the β phase at compositions H/Pd > 0.9 is reported and discussed.

Frequency dependence of HTS AC harmonic susceptibility in the Kim-Anderson and collective pinning vortex glass models

By numerically solving the nonlinear magnetic flux diffusion equation, the temperature dependence of the AC magnetic susceptibility have been computed at different frequencies in the framework of the collective pinning vortex glass and of the Kim-Anderson models. In particular the frequency dependence of the amplitude of the third harmonic have been analyzed. Such dependence is determined by the dynamic curvature of the E-J characteristics, normalized to the dynamic resistivity.

Further measurements on electrolytic cold fusion with D sub 2 O and palladium at Gran Sasso Laboratory

This paper reports on several experiments performed at the Gran Sasso Laboratory on an 0.8-cm-diam {times} 5-cm-long, hyperpure, high-temperature vacuum-annealed palladium rod used as a cathode for electrolytic infusion of D{sub 2}O and 0.1 M LiOH with regular additions of gaseous CO{sub 2} at a current density of 60 mA/cm{sup 2}. In the very low background radiation environment, several gamma bursts lasting up to 15 min were detected whose intensity, in terms of cold fusion, was {gt}10{sup {minus} 20} fusion/(deuteron pair {center dot} s). Under normal background conditions, none of these burst signals would have been detected with statistical significance. The shape and intensity of these signals are quite similar to those detected previously.

First results about hydrogen loading by means of pulsed electrolysis of Y1Ba2Cu3O7 pellets

Abstract Y 1 Ba 2 Cu 3 O 7 (YBCO) sintered pellets have been loaded at room temperature with hydrogen by means of electrolysis in an aqueous solution (LiOH 0.3 N) with μs current pulses. The superconducting features of loaded samples have been measured as a function of the temperature by the ac magnetic susceptibility. In some conditions the YBCO pellets exhibited an enhancement of the transition temperature up to 95.4 K without a significant weakening of the superconducting grain coupling. These effects appear to be strongly dependent on the loading conditions.

Frequency dependence of susceptibility higher harmonics in YBCO samples by numerical solutions of the non linear magnetic flux diffusion equation

Abstract We present a numerical analysis of the diffusion equation of the magnetic flux in YBCO in presence of ac magnetic field taking into account flux creep and flux flow. Despite critical state models, the results show the dependence of harmonic susceptibilities on the field frequency in agreement with the experimental behavior.

Hysteretic and ac dynamic losses of high T/sub c/ superconductors by numerical solution of the nonlinear magnetic diffusion equation

The complex ac susceptibility (/spl chi/) of high T/sub c/ superconducting materials has been described in terms of hysteretic and dynamic losses. By including both flux creep and flux flow resistivities in the expression of the flux flow resistivities in the expression of the flux diffusivity, induction profiles have been numerically calculated from the nonlinear flux diffusion equation. The imaginary part of /spl chi/ has been evaluated as function of temperature, frequency and amplitude of the applied magnetic field. The role of pinning and dynamic losses occuring in high T/sub c/ materials is discussed.

Deuterium overloading of palladium wires by means of high power μs pulsed electrolysis and electromigration: suggestions of a “phase transition” and related excess heat

Abstract We describe room-temperature hydrogen and deuterium loading of palladium wires by means of pulsed electrolysis and the electromigration effect. The D Pd atomic ratio has been measured by means of the dependence of the resistivity upon the D Pd ratio. Values of the D Pd ratio up to 0.95 or even higher have been reached in short times. A correlation between an anomalous temperature rise and a resistivity “transition” of the overloaded palladium clearly appears.

Frequency dependence of the higher harmonics susceptibilities of hydrogen loaded and unloaded melted YBCO samples

Abstract We measured the first and higher components of ac susceptibilities of melted YBCO samples before and after hydrogenation by μs pulsed electrolysis. First component was measured versus temperature at fixed frequency while higher harmonics were measured versus frequencies at fixed temperature near critical temperature. All measurements were performed at fixed amplitude of ac magnetic field and zero dc magnetic field. The frequency and temperature behavior of the harmonic components before and after hydrogenation gave us information on possible dynamic losses in comparison to the flux pinning mechanism.

Enhancement of critical temperature up to 100 K of YBCO ozone annealed pellets by deuterium absorption

Abstract In this paper we report preliminary results about transition temperatures of YBa 2 Cu 3 O 7 pellets loaded with high pressure deuterium gas. After the gas loading non-superconducting phases were not detected by X-ray diffraction. The complex magnetic ac susceptibility has been measured as a function of the temperature. One D-YBCO pellet exhibited a magnetic critical temperature ( T c ) as high as 100 K and the absence of a significant weakening of the superconducting grain coupling. Another sample, with a T c of 95.8 K in free air, showed a T c onset as high as 102 K under 35 bar of deuterium gas pressure.

Numerical study of the frequency and temperature dependence of the ac magnetic susceptibility in presence of a static magnetic field in HTS

The temperature dependence of the harmonics (/spl chi//sub n/) of the ac magnetic susceptibility in HTS have been investigated by numerical solutions of the non linear diffusion equation for the magnetic flux. Within the framework of the collective pinning model, we show that the transition between different regimes for the flux dynamics (taff, creep, flow) is determined by the field frequency for a fixed dc field, or by the dc field for a fixed frequency. As a consequence, a non universal behavior arises for the temperature dependence of /spl chi//sub n/. In particular, in this approach the frequency dependencies of both amplitude and temperature of the peak of the imaginary part of the first harmonic and of the modulus of the third harmonic are discussed.