This study is based on two commercially available YBCO thin films deposited by the thermal coevaporation method on different substrates (MgO and LaAlO3). Those films should be optimized for microwave applications. The structure and microstructure of the film deposited on LaAlO3 have been investigated, respectively by XRD and SEM. These characterizations showed the high quality of the films concerning the c-axis orientation and the smooth and homogenous morphology. The films have then been etched into two different coplanar line resonators by ionic method (YBCO/LaAlO3) and chemical one (YBCO/MgO) and their microwave properties have been characterized in two different cryogenic experimental set-ups. Despite the differences between these coplanar resonators, we have obtained the same intrinsic parameters (λ0 = 190 nm, T c=87 K with γ = 3) corresponding to the data provided by THEVA and a very low surface resistance (R s=0.4 m Ω at 31 K and 10 GHz).

Magnetic tunability of superconducting passive microwave devices can be done by modifying the characteristics of the medium surrounding the superconductor-based devices, in which the RF signal propagates. The variation of the permeability of a magnetic material by a DC magnetic field can achieve this objective. The magnetic material can be a ferrimagnetic material, such as a ferrite. An external DC magnetic field is used to modify the permeability of the ferrite and thus the propagation conditions. A YBCO based coplanar resonator having a resonant frequency at 5.6 GHz was used in this study. A ferrite made of calcium, vanadium and garnet (CVG) was chosen because its properties are expected to match those of YIG better for this experiment. Several positions of CVG ferrite were tried in order to get a good compromise between modulation and degradation of the properties. In the presence of a CVG plate of 500 µm thickness, at a distance of 400 µm from the superconductor, a displacement of 18 MHz of the resonant frequency has been observed for an applied field of 100 G at 77 K.

An experimental observation of the improvement of the microwave properties of high temperature superconductor thin film subjected to a weak DC magnetic field is reported. This characterization was done with two YBCO films deposited onto LaAlO3 substrates and the coplanar resonator technique was used to extract their microwave properties. The results are presented as a comparison between the behaviors of a sample that exhibits an unusual effect with another sample that has a usual behavior. To understand the origins of such a difference, the crystallographic properties and the microstructure were investigated respectively by mean of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). A major difference in terms of growth axis orientation and of granularity has been observed between the two samples. Based on the correlated variation of the surface resistance and the surface reactance of the considered sample, the presence of anomalous weak links and also of a-axis grains in one of the films could explain its unusual behavior.

An experimental study of the nonlinear effects in high temperature superconducting thin films, as a function of temperature and incident microwave power is performed. Three YBaCuO based coplanar resonators made by different techniques have been characterized. A parameter, defined as the relative variation of the unloaded quality factor between a low and a high microwave incident power, has been introduced to quantify the variation of the nonlinear effects with temperature. Results show a good correlation between measurements of the nonlinear surface resistance and the films morphology observed by scanning electron microscopy.

Cyclosporin is a very effective treatment for severe psoriasis, but its exact mechanism of action in this disease is not completely understood. It has been hypothesized that the drug could act through (lie inhibition of the expression of certain cell adhesion molecules on the keratinocytes prior to the reduction in the number of epidermal inflammatory cells. Several studies have focused on ICAM‐1 changes on keratinocytes and endothelial cells after cyclosporin treatment in psoriatic patients but their results have been somewhat contradictory. We examined changes in T‐cell markers and adhesion molecules among keratinocytes, enclothelial and inflammatory cells after low‐dose cyclosporin treatment for severe psoriasis.We performed a histological and immunohistochemical study on psoriatic skin among 10 patients (7 males and 3 females; mean age 37 years) treated with low‐dose (2.5 mg/kg/day) cyclosporin, prior to therapy, after 1 month, and after 3 months of treatment. The mean PASI (Psoriasis Area and Severity Index) before treatment was 23±4, 13±7 after the first month of therapy, and 8±2 at the end of the third month of therapy. Pretherapy samples showed a moderate to severe inflammatory infiltrate mainly clue to T‐lymphocytes expressing a T‐cell memory (UCHL‐1) and helper/inducer (CD4) phenotype. Most of these cells also expressed HLA‐DR and LFA‐1 and ICAM‐1 antigens. Alter the treatment, an overall reduction in the degree of epidermal hyperplasia was seen (p=0.01). The severity of the infiltrate was clearly reduced (p=0.05), but no significant changes in the phenotype profile were observed. Although slightly reduced, endothelial ICAM‐1 expression persisted after cyclosporin therapy. Keratinocyte ICAM‐1 expression was uniformly and significantly reduced after 1 month and 3 months of therapy (p=0.01). These results support the hypothesis that cyclosporin interferes with the expression of keratinocyte adhesion molecules in patients with psoriasis.

Renal transplant recipients have a high incidence of cutaneous complications such as neoplasia and viral or fungal infections. Morphologic alterations of epidermal Langerhans cells (LC) have furthermore been described in these patients. Since these changes have been mainly found in sun‐exposed skin, a direct effect of immunosuppressive therapy remains a matter of discussion. A quantitative and morphometric study of epidermal LC in non‐exposed skin was performed in 28 renal transplant patients (RTF). RTF were divided in two groups according to immunosuppressive treatment: group A; azathioprine + prednisone (14 cases) and group B; cyclosporine + prednisone (14 cases). Twenty sex‐age matched non‐immunosuppressed patients acted as controls (group C). Epidermal sheets were obtained by incubation in EDTA and stained for ATPase activity and with the monoclonal antibody T6 (CDI) using the avidin‐biotin peroxidase method. Langerhans cells were counted using a calibrated graticule (400×) and expressed as the mean number of LC/mm2. The mean area of the LC and the number of primary dendrites (pd) and secondary dendrites (sd) were determined with a morphometer adapted to an Apple II computer. The mean number of positive cells in controls was: ATPase, 677±157; T6, 695±164. Patients in group A had the maximum reduction in both ATPase and T6 LC density (ATPase, 339±142, T6, 402±194). Patients in group B had an intermediate reduction in the number of LC (ATPase, 494±121; T6, 529±112). The mean area of the LC and mean number of primary but not sd were significatively higher in RTP (area = 274±65 μ2; pd = 3.1±0.3) than in controls (area = 213±62 μ2; pd = 2.8±0.3). We conclude that RTP have a diminished number of LC in non‐exposed skin and that this decrease is more pronounced in patients receiving azathioprine and prednisone than in patients receiving cyclosporin and prednisone. Langerhans cells in RTP also show hypertrophic changes. These results suggest a role for the immunosuppressive therapy in the pathogenesis of the LC alterations in RTP.