Transport properties and the anisotropy of Ba_{1-x}K_xFe_2As_2 single crystals in normal and superconducting states

The transport and superconducting properties of Ba_{1-x}K_xFe_2As_2 single crystals with T_c = 31 K were studied. Both in-plane and out-of plane resistivity was measured by modified Montgomery method. The in-plane resistivity for all studied samples, obtained in the course of the same synthesis, is almost the same, unlike to the out-of plane resistivity, which differ considerably. We have found that the resistivity anisotropy \gamma=\rho_c /\rho_{ab} is almost temperature independent and lies in the range 10-30 for different samples. This, probably, indicates on the extrinsic nature of high out-of-plane resistivity, which may appear due to the presence of the flat defects along Fe-As layers in the samples. This statement is supported by comparatively small effective mass anisotropy, obtained from the upper critical field measurements, and from the observation of the so-called "Friedel transition", which indicates on the existence of some disorder in the samples in c-direction.Comment: 5 pages, 5 figure

Aerodynamic simulation of vertical-axis wind turbines

Full-scale, 3D, time-dependent aerodynamics modeling and simulation of a Darrieustype vertical-axis wind turbine (VAWT) is presented. The simulations are performed using a moving-domain finite-element-based ALE-VMS technique augmented with a sliding-interface formulation to handle the rotor-stator interactions present. We simulate a single VAWT using a sequence of meshes with increased resolution to assess the computational requirements for this class of problems. The computational results are in good agreement with experimental data. We also perform a computation of two side-by-side counterrotating VAWTs to illustrate how the ALE-VMS technique may be used for the simulation of multiple turbines placed in arrays

DOI:10.1068/htwu215 Experimental investigation of solid and liquid zirconium

Abstract. An electrical pulse current of 3 ^ 5 kA during 3 ^ 5 ms was used to heat zirconium tapes of foils. The tapes (width 1 ^ 2 mm and length 30 mm) were placed in a chamber under 1 bar ambient air atmosphere. Specific enthalpy, resistivity, temperature, and specific heat capacity in solid and liquid states (up to 2350 K) were measured. Temperature was measured (from 1800 up to 2350 K) by a fast optical pyrometer through a quartz light guide. For registration of current through the specimen, the voltage across it, and the pyrometer signal, a digital 4-channel oscilloscope was used. The following thermophysical properties are presented in the temperature range 1800 ^ 2350 K: specific enthalpy, at the start of melting; specific enthalpy, at the end of melting; heat of melting; specific heat capacity of the solid state (from 1800 K up to melting); specific heat capacity of the liquid state (from 2150 K up to 2350 K). The dependence of resistivity (referred to initial dimensions) against specific enthalpy was obtained for the solid and liquid states (from room temperature up to 2350 K). The dependence of resistivity (referred to initial dimensions) against temperature was obtained for the solid and liquid states (from temperature 1800 K up to 2350 K). Additional information was obtained for the phase transition in the solid state for zirconium. Specific enthalpy for the start and the end of the transition, the heat of transition, and resistivity (referred to initial dimensions) in both states were measured.