[en] Conventional power transformers are very simple and reliable electrical components and their efficiency, for large power rating, is well above 99 %. With such an excellent performance the improvement margin seems very limited. However, due to the large amount of power managed and the continuous service, also a small increase in the efficiency is desirable. As an example, consider that an efficiency increase of 0.5 % of a 25 MVA transformer may lead to savings in the order of 100 k euro/year. The use of superconducting materials opens the way to efficiency improvements on power transformers, and also adds important advantages such as size and weight reduction, that are very attractive for urban substations and transport applications. Moreover superconductors eliminate the need for refrigeration oil, thus avoiding the risk of fire hazard and reducing the environmental impact, in accordance with recent EU guidelines. In this paper a design procedure for HTS power transformers is reported. This procedure, that includes an analytical method for the calculation of the AC losses, is used to design a 25 MVA - 154 kV / 20 kV transformer based on commercial BSCCO tapes, and the evaluated performance are compared with those of a conventional copper transformer. The optimal working temperature is evaluated, and allowable cooling technologies are discussed. Considerations on the use of future 2nd generation YBCO coated conductors are also reported

[en] A case is described of a rare mediastinic mass extensively calcified and occasionally found. The contribution to diagnosis offered by computerized tomography is pointed out

[en] Aging and female sex are major risk factors for cholesterol gallstones: in addition to hepatic secretion of lithogenic bile, decreased gallbladder contractility may play a role in such physiological conditions. This study was aimed at evaluating the effect of age and sex on gallbladder kinetics in healthy subjects. Gallbladder volume was measured on the US images of 157 fasting subjects using the sum-of-cylinders method. No significant difference was observed between males and females. On the contrary, age was shown to have a significant positive correlation with fasting gallbladder volume, particulary in males. In a second group of 63 healthy volunteers gallbladder volumes were evaluated both before and after a standard meal. The subjects were grouped according to age, and fasting gallbladder volume appeared to be significantly greater in the groups formed by older people. Gallbladder volumes were compared in younger groups (under 35), and gallbladder emptying resulted to be much more complete in males than in females. On the contrary, no significant differences was observed between males and famales over50 - which suggests a possible role of sex - and age-related hormonal factors. The above changes in gallbladder function may facilitate bile stasis which might in turn contribute to the increased risk for cholesterol gallstones notoriously associated with advanced age and female sex

No abstract available

[en] The article introduces the models and methodologies developed for sizing and for comparative analysis of impacts in life cycle assessment of innovative transformers size 25 MVA based on high critical temperature conductors

[en] The investigation of quenching in low temperature superconducting wires is of great relevance for a proper design of superconductive cables and magnets. This paper reports the experimental results of a vast measurement campaign of quench induced by laser pulses on NbTi and Nb₃Sn wires in pool boiling helium I. A comparison of the quench behavior of two typical NbTi and Nb₃Sn wires is shown from different standpoints. Different qualitative behaviors of the voltage traces recorded during quenches and recoveries on NbTi and Nb₃Sn wires are reported and analyzed. It is shown that the Nb₃Sn wire exhibits a quench or no-quench behavior, whereas quenches and recoveries are exhibited by the NbTi wire. The two wires are also compared by considering the behaviors of the two main parameters describing quench, i.e. quench energies and quench velocities, with respect to operating current, pulse duration, and magnetic field. It is shown that the Nb₃Sn wire exhibits a 'kink' of the quench energy versus current curve that makes the quench energy of Nb₃Sn lower than that of NbTi at some intermediate current levels. Both the qualitative differences of the voltage traces and the different behaviors of quench energies and velocities are interpreted through a coupled electromagnetic-thermal model, with special emphasis on the detailed description of heat exchange with liquid helium.

[en] The stability of superconducting wires is a crucial task in the design of safe and reliable superconducting magnets. These magnets are prone to premature quenches due to local releases of energy. In order to simulate these energy disturbances, various heater technologies have been developed, such as coated tips, graphite pastes, and inductive coils. The experiments studied in the present work have been performed using a single-mode diode laser with an optical fiber to illuminate the superconducting strand surface. Minimum quench energies and voltage traces at different magnetic flux densities and transport currents have been measured on an LHC-type, Cu/NbTi wire bathed in pool boiling helium I. This paper deals, with the numerical analysis of the experimental data. In particular, a coupled electromagnetic and thermal model has been developed to study quench development and propagation, focusing on the influence of heat exchange with liquid helium. (authors)

[en] The realization and connection to the electrical grid of large scale generating plants exploiting renewable sources such as solar or wind can be prevented by problems of grid stability and power management. This problem can be solved by introducing adequately large energy storage systems. One of the most promising and studied technologies for large storage of energy in chemical form is the production of hydrogen by water electrolysis, which can be stored and transported in compressed or liquid form. Liquefaction is a high energy consuming process, but allows higher storage densities and can represent the appropriate solution when large scale hydrogen storage and long range transport is needed. For similar reasons, today, increasing quotas of natural gas are transported in liquid form. Current vaporization systems directly provide heat absorbed from the environment or produced by burning part of the output of gasified fuel. Advanced systems aimed at recovering part of the energy spent for liquefaction of natural gas have been proposed and tested. In this paper, we consider achievable advantages of realizing recovery systems in view of the future use of liquid hydrogen (LH₂) as energy vector. The maximum outcomes of ideal thermal systems is evaluated. Then, different gas turbine (GT), magnetohydrodynamic (MHD) generator and combined systems are considered and compared, both with ideal recovery systems and with conventional vaporizing and power generating systems