M R Osorio

Transition to the normal state of superconducting Y1Ba2Cu3O7-δ thin films induced by high current densities

We report measurements at zero applied magnetic field of the characteristic curves (E-J) in Y1Ba2Cu3O7-δ thin films in the high current density regime, up to current densities which induce the transition to the normal state. To minimize spurious heating effects due to Joule dissipation, the E-J curves were measured with a pulse technique and with the samples submerged in a liquid nitrogen bath, changing the temperature by varying the nitrogen vapour pressure. This experimental set-up allows us to observe not only the abrupt voltage jump appearing at current densities J* much larger (typically one order of magnitude) than the critical current density, Jc, but also the entire transition up to the normal state. Our results show that the product J*ρn is roughly sample independent, ρn being the slope of the E-J curves for J>J*. This finding is in qualitative agreement with the existing models that explain the jump at J* in terms of a vortex instability at high flux-flow velocities.

Extending the range of applicability of HTS cylinders in inductive superconducting fault current limiters

Here, we study the behaviour of an inductive superconducting fault current limiter (SFCL) whose secondary is a bulk cylinder with an array of appropriately distributed weak zones. This design allows heat to be removed by conduction from the hot weak zones, which absorb the power dissipation, to the remaining colder parts of the cylinder. Our work highlights the possibility of overcoming the limitations of high power SFCLs based on bulk cylinders, which present recovery time values well beyond the maximum value tolerated in a distribution line.

Optimal refrigeration of bulk superconducting elements in fault current limiters by using artificial weak zones

We have suggested recently that the introduction of artificial weak zones (AWZ) in the superconducting elements used in fault current limiters (FCL) could greatly improve the recovery time after a quench provoked by the FCL activation. In this work, a finite element method (FEM), based on the thermal and electrical equations describing the behaviour of samples when the normal?superconducting transition occurs, is used to study the thermal evolution during the whole quenching?recovery process of high temperature superconducting rings with grooves, which act as AWZ. Our simulations allow us to set the size of grooves and the more suitable material properties to obtain a better sample refrigeration.

Quench and thermal recovery in a superconducting fault current limiter with artificial weak zones

We report results on the behaviour of an inductive fault current limiter prototype with weak zones artificially created. The superconducting elements are Bi-2223 rings and the tests have been realized with the device on a Helium gas environment at 77.3 K. We found that the artificial weak zones can play the main role during the limitation under a current fault and on the thermal recovery process after the fault, which could be used to improve the performance of these devices. Our results show also that the artificial weak zones could balance, in addition, the influence of other natural defects which could lead to non-uniform normal-superconducting transitions, the formation of hot spots, etc.

Behaviour of different artificial weak zones in superconducting elements working in inductive fault current limiters

The thermal recovery of superconducting elements working as secondaries in fault current limiters can be enhanced by taking advantage of the removal of heat by conduction from an array of artificial weak zones (AWZ) distributed along the superconductor perimeter (hot parts) to the non-weak segments (cold parts). These results were obtained by studying samples with weak parts in the shape of grooves, all identical in size. In this paper we consider the case in which one of the AWZ is slightly different from the rest. Our results show that a change in its length has a negligible effect. On the contrary, a groove which is slightly deeper can be overheated and hence can strongly determine the recovery time of the whole limiter.

Superconducting microlimiters based on YBCO thin-films grown on SrTiO3 substrates

It has been shown recently that superconducting microbridges implemented with YBa2Cu3O7−δ (YBCO) thin-films grown on sapphire substrates could be used as very efficient fault current limiters for microelectronic devices with some elements working at temperatures below TcI the superconducting critical temperature and, simultaneously, under very low power conditions (below 1 W). These so-called microlimiters are then well adapted to important applications of the superconducting microelectronics, as infrared detectors or SQUID based electronics. Here we will present new results obtained by using YBCO microbridges grown on SrTiO3 substrates, which have a thermal conductivity of the order of 50 times lower than the sapphire substrates used in most of our previous work. These new measurements confirm the important role played in the behaviour of microlimiters by the thermal exchanges between the microbridges with their substrates and between these last with their environment. Our present results also show that the temperature for optimal operation of the microlimiter is substrate-dependent.

The impedance of inductive superconducting fault current limiters operating with stacks of thin film Y123/Au washers or bulk Bi2223 rings as secondaries

Inductive fault current limiters operating with stacks of various small superconducting elements acting as secondaries were studied. The stacks consist of Y1Ba2Cu3O7?? thin film washers or Bi1.8Pb0.26Sr2Ca2Cu3O10+x bulk rings. A central result of our work is an experimental demonstration that the limiting capability of the device is strongly reduced when several bulk rings are stacked, whereas it remains almost unchanged for thin film washers. The use of thin films should therefore allow us to build more efficient high power inductive limiters based on stacks of small washers.

Specific Immunotherapy Modified T-Cells Responses In a Spanish Population Of Der p Allergic Patients

T U E S D A Y 966 Nanoparticle Engineering For The Immunomodulation Of Dendritic Cells Dr. Xavier le Guevel, PhD, Dr. Tah ia Fern andez, PhD, Dr. Adriana Ariza, PhD, Dr. Maria Isabel Monta~nez, PhD, Dr. Maria J. Torres, MD, PhD, Dr. Cristobalina Mayorga, PhD, Dr. Miguel Blanca, MD, PhDBionand, Campanillas, Spain.Research Laboratory FIMABIS Foundation, M alaga, Spain.Research Laboratory forAllergicDiseases, Hospital Regional Universitario deMalaga FIMABIS-IBIMA,Malaga, Spain.Research Laboratory for Allergic Diseases, Hospital Regional Universitario de Malaga IBIMA, M alaga, Spain.Allergy Service, Carlos Haya Hospital, M alaga, Spain.ResearchLaboratory,CarlosHayaHospital-FIMABIS,M alaga, Spain. RATIONALE: Nanotechnology and particularly nanoparticles (NPs) have gained a tremendous interest over the last 10 years in the field of immunotherapy. One of the most successful strategies of using NPs for specific immunotherapy is based on targeting dendritic cells (DCs), which play a central role on the activation of the immune system. Engineered nanoparticles can specifically be designed to either target or avoid interactions with the immune system leading to an immune stimulation or and immunosuppression responses. However, the understanding through systematic studies on the exact effect of size, shape or surface charge of NPs to the interaction and the immune response of DCs remains unclear. We aim to assess the impact of gold NPs with different physicochemical parameters to the immunological response of DCs. METHODS: Thus, immature DCswere incubatedwith a series of goldNPs of the same size (AE;15nm) with ligands containing different charges (methyl, zwitterionic, amine, hydroxyl and carboxyl) on their surface. Their capacity to induce maturation and T-cell proliferation were investigated. Biodistribution of NPs in cells was determined by fluorescence microscopy. RESULTS: First results indicate a significant influence of the surface chemistry of NPs with different levels of DCs maturation and T-cell proliferation. Investigation of the NPs biodistribution suggests a decrease of the non-specific binding for the pegylated NPs in DCs with an internalization in the cytoplasm by an endocytotic process. CONCLUSIONS: These results are encouraging to develop smart carriers for target inflammatory and inflammation-associated disorders.

Thin-film washers as secondaries in superconducting inductive fault current limiters: the role of the cooling atmosphere

Recently, we showed that the use of thin-film superconducting washers as secondaries in inductive fault current limiters may have considerable advantages when compared with the more conventional bulk rings or cylinders. Here we extend those previous works to determine if the cooling atmosphere plays a significant role on the recovery time, τR, of the inductive fault current limiter based on thin film superconductors. We have used helium as a cooling gas, from primary vacuum to atmospheric pressure. We have found that gas pressure has an appreciable influence on the recovery time of our inductive fault current limiter. For instance, our results show that τR under atmospheric pressure is almost thirty per cent shorter than when measured in primary vacuum. A numerical simulation realized by the finite element method shows that just after the fault the substrate is thermalized and, therefore, during the recovery convection is the only working heat exchange mechanism. To avoid this undesirable thermalization and to further reduce the recovery time the substrate should either be much more thicker or be in good contact with a thermal sink capable of removing the heat by conduction.