AC losses in superconducting composite strips in a magnetic field in the form of a standing wave

Analytical expressions for the evaluation of AC losses in a superconductor-metal composite strip in a nonuniform AC magnetic field having the form of a standing wave are derived. The considered configuration models superconducting tapes, thin films and coated superconductors. A distinctive feature of the problem is the appearance of a transverse component of the induced current that converts the problem to a two-dimensional one. Bean's critical state model for a superconductor and a low frequency approximation for a metal are used. In the framework of this approximation the influence of eddy currents in the metal on the magnetic field is neglected, and the current distribution in the superconductor is determined by an external field. Two cases were considered: (1) superconducting and metal strips electrically separated; (2) they are in an electric contact. It is shown that for most practical cases enough to take into account only the losses generated by induced longitudinal currents in a composite strip. When an electric contact between strips exists, the maximum loss density in high fields (above 2 T) can be determined by the transverse component of the current.Comment: 18 pages, 10 figure

Exact solution of the one-dimensional spin-32\frac32 Ising model in magnetic field

In this paper, we study the Ising model with general spin $S$ in presence of an external magnetic field by means of the equations of motion method and of the Green's function formalism. First, the model is shown to be isomorphic to a fermionic one constituted of $2S$ species of localized particles interacting via an intersite Coulomb interaction. Then, an exact solution is found, for any dimension, in terms of a finite, complete set of eigenoperators of the latter Hamiltonian and of the corresponding eigenenergies. This explicit knowledge makes possible writing exact expressions for the corresponding Green's function and correlation functions, which turn out to depend on a finite set of parameters to be self-consistently determined. Finally, we present an original procedure, based on algebraic constraints, to exactly fix these latter parameters in the case of dimension 1 and spin $\frac32$. For this latter case and, just for comparison, for the cases of dimension 1 and spin $\frac12$ [F. Mancini, Eur. Phys. J. B \textbf{45}, 497 (2005)] and spin 1 [F. Mancini, Eur. Phys. J. B \textbf{47}, 527 (2005)], relevant properties such as magnetization $$and square magnetic moment$$, susceptibility and specific heat are reported as functions of temperature and external magnetic field both for ferromagnetic and antiferromagnetic couplings. It is worth noticing the use we made of composite operators describing occupation transitions among the 3 species of localized particles and the related study of single, double and triple occupancy per site

Current and efficiency optimization under oscillating forces in entropic barriers

The transport of externally overdriven particles confined in entropic barriers is investigated under various types of oscillating and temporal forces. Temperature, load, and amplitude dependence of the particle current and energy conversion efficiency are investigated in three dimensions. For oscillating forces, the optimized temperature-load, amplitude temperature, and amplitude-load intervals are determined when fixing the amplitude, load, and temperature, respectively. By using three-dimensional plots rather than two-dimensional ones, it is clearly shown that oscillating forces provide more efficiency compared with a temporal one in specified optimized parameter regions. Furthermore, the dependency of efficiency to the angle between the unbiased driving force and a constant force is investigated and an asymmetric angular dependence is found for all types of forces. Finally, it is shown that oscillating forces with a high amplitude and under a moderate load lead to higher efficiencies than a temporal force at both low and high temperatures for the entire range of contact angle

A sparse data fast Fourier transform (SDFFT) - Algorithm and implementation

An algorithm that efficiently Fourier transforms sparse spatial data to sparse spectral data with controllable error is presented. Unlike the ordinary nonuniform last Fourier transform (NUFFT), which becomes O(N 2) for sparse k-space and sparse k-space data, the sparse data fast Fourier transform (SDFFT) presented herein decreases the cost to O(N log N) while preserving the O(N log N) memory complexity. The algorithm can be readily employed in general signal processing applications where only part of the k-space is to be computed - regardless of whether it is a regular region like an angular section of the Ewald's sphere or it consists completely of arbitrary points. Among its applications in electromagnetics are back-projection tomography, diffraction tomography, synthetic aperture radar imaging, and the computation of far field patterns due to general aperture antennas and antenna arrays.link_to_subscribed_fulltex

A stability assessment of the rockfall problem around the Gokgol Tunnel (Zonguldak, Turkey)

WOS: 000413673700002The stability of rock slopes is an important area of interest in civil and mining engineering. This study investigated rockfall occurring around the Gokgol tunnel along the Zonguldak-Ankara roadway. Extensive field studies, including determination of geological description of the rock mass, scan-line surveys on discontinuities, identification of slope profiles, measurement of actual fallen block dimensions, and sampling procedures, were carried out. The study area and its surroundings are part of a Lower Carboniferous limestone formation. The assessments based on field studies indicated that two joint sets and a bedding plane were the main types of discontinuity. Two slope profiles were then created by considering the most frequently encountered rock fall events. The present study aimed to investigate the rockfall potential in this area by means of numerical analyses. For this purpose, RocFall software based on the lumped-mass method was utilized. Based on these analyses, traffic safety is threatened by potential rockfall. In Case I, a 30 % portion of the falling blocks reached the side of the main road, while about 70 % of them remained on the slope. However, falling blocks reached the end of the road in Case II. The study area requires some protection measures, such as the construction of retaining barriers and steel mesh to hold small size rock blocks. As a result, barrier heights to hold falling blocks were calculated as 0.5 m and 4 m for Case I and Case II, respectively. Barrier heights sufficient to hold falling rocks were determined using numerical analysis. In Case II, from such analyses, the energy required for a protection barrier for 1000 kg was found to be 200 kJ

3-D imaging of large scale buried structure by 1-D inversion of very early time electromagnetic (VETEM) data

A simple and efficient method for large scale three-dimensional (3-D) subsurface imaging of inhomogeneous background is presented. One-dimensional (1-D) multifrequency distorted Born iterative method (DBIM) is employed in the inversion. Simulation results utilizing synthetic scattering data are given. Calibration of the very early time electromagnetic (VETEM) experimental waveforms is detailed along with major problems encountered in practice and their solutions. This discussion is followed by the results of a large scale application of the method to the experimental data provided by the VETEM system of the U.S. Geological Survey. The method is shown to have a computational complexity that is promising for on-site inversion.link_to_subscribed_fulltex