Critical State Flux Penetration and Linear Microwave Vortex Response in YBa_2Cu_3O_{7-x} Films

The vortex contribution to the dc field (H) dependent microwave surface impedance Z_s = R_s+iX_s of YBa_2Cu_3O_{7-x} thin films was measured using suspended patterned resonators. Z_s(H) is shown to be a direct measure of the flux density B(H) enabling a very precise test of models of flux penetration. Three regimes of field-dependent behavior were observed: (1) Initial flux penetration occurs on very low field scales H_i(4.2K) 100Oe, (2) At moderate fields the flux penetration into the virgin state is in excellent agreement with calculations based upon the field-induced Bean critical state for thin film geometry, parametrized by a field scale H_s(4.2K) J_c*d 0.5T, (3) for very high fields H >>H_s, the flux density is uniform and the measurements enable direct determination of vortex parameters such as pinning force constants \alpha_p and vortex viscosity \eta. However hysteresis loops are in disagreement with the thin film Bean model, and instead are governed by the low field scale H_i, rather than by H_s. Geometric barriers are insufficient to account for the observed results.Comment: 20 pages, LaTeX type, Uses REVTeX style files, Submitted to Physical Review B, 600 dpi PostScript file with high resolution figures available at http://sagar.physics.neu.edu/preprints.htm

C-axis Penetration Depth and Inter-layer Conductivity in the Thallium Based Cuprate Superconductors

The c-axis Josephson plasmon in optimally doped single-layer and bi-layer high Tc cuprates Tl2201 and Tl2212 have been investigated using infrared spectroscopy. We observed the plasma frequencies for these two compounds at 27.8 and 25.6 cm-1 respectively, which we interpret as a Josephson resonance across the TlO blocking layers. No maximum in the temperature dependence of the c-axis conductivity was observed below Tc, indicating that even in the superconducting state a coherent quasi-particle contribution to the c-axis conductivity is absent or very weak, in contrast to the behaviour of the ab-plane conductivity.Comment: 4 pages, 3 figure

Microwave Current Imaging in Passive HTS Components by Low-Temperature Laser Scanning Microscopy (LTLSM)

We have used the LTLSM technique for a spatially resolved investigation of the microwave transport properties, nonlinearities and material inhomogeneities in an operating coplanar waveguide YBa_2Cu_3O_{7-\delta} (YBCO) microwave resonator on an LaAlO_3 (LAO) substrate. The influence of twin-domain blocks, in-plane rotated grains, and micro-cracks in the YBCO film on the nonuniform rf current distribution were measured with a micrometer-scale spatial resolution. The impact of the peaked edge currents and rf field penetration into weak links on the linear device performance were studied as well. The LTLSM capabilities and its future potential for non-destructive characterization of the microwave properties of superconducting circuits are discussed.Comment: 8 pages, 9 figures, 2-column format, presented at High Temperature Superconductors in High Frequency Fields 2004, Journal of Superconductivity (in press

A large-scale field experiment on salt marsh construction

Salt marshes provide important natural habitats, mitigate effects of subsidence and sea level rise and help in coastal defence. Commissioned by the municipality of Delfzijl, the EcoShape consortium obtained the opportunity to carry out a large-scale field experiment on salt marsh construction as part of their Living Lab for MUD

External validation of the Motivation To Stop Scale (MTSS): findings from the International Tobacco Control (ITC) Netherlands Survey

BACKGROUND: The Motivation To Stop Scale (MTSS) is a single-item instrument which has been shown to predict quit attempts in the next 6 months in a previous validation study conducted in England. The aim of the current study was to determine the external validity of the MTSS among Dutch smokers in predicting quit attempts in the next 12 months. A secondary aim was to compare the discriminative accuracy of the MTSS with that of a Stages of Change assessment. METHODS: We analysed data from three consecutive waves of the International Tobacco Control (ITC) Netherlands Survey (n = 1272). We conducted logistic regression analyses with the baseline score of the MTSS (measured in 2012 or 2013) predicting a quit attempt in the next 12 months (measured in 2013 or 2014). We furthermore compared the area under the Receiver Operating Characteristics (ROCAUC) curves of the MTSS and a Stages of Change measure. RESULTS: A total of 450 smokers (35.4%) made a quit attempt between baseline and 12-month follow-up. The regression analysis showed a positive relationship between scoring on the MTSS and quit attempts (odds ratio = 18.15, 95% confidence interval = 8.12-40.58 for the most vs. least motivated group). The discriminative accuracy of the MTSS (ROCAUC = 0.68) was marginally higher than that of a Stages of Change assessment (ROCAUC = 0.65), but not statistically significant (P = 0.21). CONCLUSION: The MTSS is an externally valid instrument to predict quit attempts in the next 12 months