A. Öztürk

Fabrication and characterization of Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06O10 superconductors prepared by a wet technique

Abstract We have carried out measurements of resistivity on Bi1.84Pb0.34Sr1.91Ca2.03Cu3.06O10 granular samples prepared by the liquid ammonium nitrate method. The standard four-probe technique was used to measure the resistivity and the critical current of the specimen. We estimated the irreversibility line from the broadening of the resistive–superconducting transition in external DC magnetic fields up to 447 mT for the sample fabricated. A non-linear Arrhenius plot of resistive tail has been found. The power law relation RBirr=B0(1−T/Tc)3/2 gives a good fit to our data obtained from zero-resistivity temperature in selected magnetic fields. We have also characterized the prepared samples in terms of XRD, SEM and critical currents.

Magnetic responses of a high-Tc semi-reversible YBCO superconductor

We report the magnetic responses of a YBCO superconducting sample prepared by solid-state reaction method, in terms of d.c. magnetization, and a.c. susceptibility. Hysteresis loops have been analyzed in the framework of critical state model including the Meissner current. The critical current as a function of temperature and the volume fraction of the grains have been estimated from the a.c. susceptibility data. The zero resistance temperature and diamagnetic onset temperature were found to be 90 and 91.5 K respectively.

AC loss study by AC susceptibility measurement in a commercial Bi:2223/Ag tape prepared by the CTFF method: H \parallel c axis and short specimen

The effect of temperature, field amplitude, frequency and orientation of the field on AC losses in a commercial Bi:2223/Ag tape prepared by the continuous filling and forming (CTFF) method has been investigated. The measurements were performed using an AC susceptometer. The experimental results show that the losses depend on field amplitude, temperature, DC field, orientation of the sample and strongly on frequency. Due to the strong dependence of AC losses on frequency, measurements were pursued at several frequencies between 20 Hz and 10 kHz at various temperatures (10, 20, 30 and 77 K). The strong frequency dependence at these low temperatures is attributed to eddy current losses and/or inter-filamentary coupling losses. At higher temperatures and low frequencies, the main contribution to AC losses comes from hysteresis losses due to the flux entry into and exit from the superconducting tape during the up and down swings of the magnetic field. We have calculated coupling losses as a function of frequency and temperature-dependent time constant. Experimental data are analyzed by comparing them with the calculated curves. From the DC field dependence of the AC susceptibility, we obtained the irreversibility line.

Automatic building extraction from very high-resolution image and LiDAR data with SVM algorithm

Recent developments in the field of remote sensing have introduced new sensor technologies in usage of LiDAR, SAR, and high-resolution optical data. Classification performance is expected to increase through combining these various data sources. The purpose of this study is to develop a new approach for automatic extraction of buildings in urbanized and suburbanized areas. For this purpose, multi-feature extraction process including the spatial, spectral, and textural features were conducted on the very high spatial resolution multispectral aerial images and the LiDAR data set. SVM algorithm was trained by using this multi-feature data, and the classification was performed. After the classification of building and non-building, objects were extracted with high accuracy for the test areas. As a result, it has been proven that multi-features derived from combination of optical and LiDAR data can be successfully applied to solve the problem of automatic detection of buildings by using the proposed approach.

Determination of the material parameters of a melt-textured YBCO superconductor by DC magnetization analysis

Abstract We report the isothermal magnetization curves of a YBCO superconducting sample prepared by a flame-quench–melt-growth (FQMG) method. Hysteresis loops have been calculated and analyzed in the framework of a critical state model including the Meissner current. The bulk critical current and Meissner current as a function of applied field were extracted, and the volume fraction of the grains, f g , has been estimated to be 0.64 from a comparison of the theoretical and experimental M–H hysteresis loops. The lower critical field, μ 0 H c1 , was found to be 14.4 mT.

Flux trapping properties of Bi(Pb)-Sr-Ca-Cu-O superconducting hollow cylinder: the effect of azimuthal flux on flux trapping in the cavity

Abstract The remanent magnetic flux density trapped in the cavity of a sintered tube of (Bi 0.9 Pb 0.1 ) 2 (Sr 2 Ca 2 Cu 3 O 10 ) has been carried out as a function of H cool , the axial magnetic field present during field cooling (FC) which is then removed, and of H cycle , the axial magnetic field impressed and removed after zero field cooling (ZFC). The dependence of the critical current density in the matrix, j cm and in the grain, j cg , on the magnetic field was estimated from the experimental data using the model developed by Celebi and LeBlanc. The effect of azimuthal flux on flux trapping in the cavity was also explored.