We consider a gas of N(= 6, 10, 15) Bose particles with hard-core repulsion, contained in a quasi-2D harmonic trap and subjected to an overall angular velocity Ω about the z-axis. Exact diagonalization of the n × n many-body Hamiltonian matrix in given subspaces of the total (quantized) angular momentum Lz, with n ∼ 10 5 (e.g. for Lz=N=15, n =240782) was carried out using Davidson's algorithm. The many-body variational ground state wavefunction, as also the corresponding energy and the reduced one-particle density-matrix ρ (r, r ′ ) = µ λµχ * µ (r) χµ (r ′ ) were calculated. With the usual identification of Ω as the Lagrange multiplier associated with Lz for a rotating system, the Lz − Ω phase diagram (or the stability line) was determined that gave a number of critical angular velocities Ωci, i = 1, 2, 3, · · · , at which the ground state angular momentum and the associated condensate fraction, given by the largest eigenvalue of the reduced one-particle density-matrix, undergo abrupt jumps. A number of (total) angular momentum states were found to be stable at successively higher critical angular velocities Ωci, i = 1, 2, 3, · · · for a given N. All the states in the regime N > Lz > 0 are metastable. For Lz >N, the Lz values for the stable ground states generally increased with the increasing critical angular velocities Ωci, and the condensate was strongly depleted. The critical Ωci values, however, decreased with increasing interaction strength as well as the particle number, and were systematically greater than the non-variational Yrast-state values for the single vortex state with Lz=N. We have also observed that the condensate fraction for the single vortex state (as also for the higher vortex states) did not change significantly even as the 2-body interaction strength was varied over several(∼ 4) orders of magnitude in the moderately to the weakly interacting regime.

This paper presents, with a live field experiment, the potential of increasing wind farm power generation by optimally yawing upstream wind turbine for reducing wake effects as a part of the SmartEOLE project. Two 2MW turbines from the Le Sole de Moulin Vieux (SMV) wind farm are used for this purpose. The upstream turbine (SMV6) is operated with a yaw offset ( α ) in a range of − 12 ° to 8° for analysing the impact on the downstream turbine (SMV5). Simulations are performed with intelligent control strategies for estimating optimum α settings. Simulations show that optimal α can increase net production of the two turbines by more than 5%. The impact of α on SMV6 is quantified using the data obtained during the experiment. A comparison of the data obtained during the experiment is carried out with data obtained during normal operations in similar wind conditions. This comparison show that an optimum or near-optimum α increases net production by more than 5% in wake affected wind conditions, which is in confirmation with the simulated results.

We have employed first principles calculations to study the electronic structure and magnetic properties of the low-dimensional phosphates, Ba2Cu(PO4)2 and Sr2Cu(PO4)2. Using the selfconsistent tight binding linearized muffin-tin orbital (TB-LMTO) method and the N th order muffin tin orbital (NMTO) method we have calculated the various intrachain as well as the interchain hopping parameters between the magnetic ions (Cu 2+ ) for both the compounds. We find that the nearest-neighbor intrachain hopping (t) is the dominant interaction suggesting the compounds to be indeed one-dimensional. Our analysis of the band dispersion, orbital projected band structures and the hopping parameters confirms that the Cu 2+ -Cu 2+ super-super exchange interaction takes place along the crystallographic b-direction mediated by O-P-O. We have also analyzed in details the origin of short range exchange interaction for these systems. Our ab-initio estimate of the ratio of the exchange interaction of Sr2Cu(PO4)2 to that of Ba2Cu(PO4)2 compares excellently with available experimental results.

An experimental study is carried out on a parallel triangular finned tube array with P/Deff ratio 1.62 to examine the effect of fin geometry on flow-induced vibration response. Fins on a tube increase the heat transfer rate but these also affect the fluid dynamics around the tube. The flow pattern across the finned tubes is complex as compared to bare tube arrays. There are numerous parameters that affect the finned tube vibration subjected to air cross-flow in a tube array. In the current study, some of these parameters i.e. fin thickness and fin density are focused and their effects on flow-induced vibration response are analyzed in different rows of fin tube array. The current experimentation is performed in a subsonic wind tunnel using a single flexible Aluminum finned tube in a rigid array. Seven tubes with similar specifications but distinct fin thickness and fin density are used for the testing purpose. Their amplitude response suggests that the flowinduced vibration behavior is greatly affected by changing the finned tube parameters. It has also been observed during spectral analysis that the Strouhal number is independent of fin geometry since it remained constant in different rows of the array for finned tubes under study. It suggests that the vortex shedding has also contributed towards the finned tube vibration predominantly in the first, second and the fourth row of tube array.

Thermal conductivity κ(T) and thermoelectric power S(T) studies on (Y,Gd)Ba2(Cu1−xMnx)3O7−δ (x≤0.02) superconductors are presented here. Thermal conductivity for all the samples exhibits a hump below the superconducting transition temperature Tc. The peak height of the hump decreases with the Mn content in both the Y- and Gd-based systems, barring GdBa2(Cu0.99Mn0.01)3O7−δ. The peak height reduction in the Gd-based cuprates is much faster (∼one fourth) compared to the Y-based samples. The thermoelectric power (TEP) of the Y-based samples for x≤0.0075 is electron-like (up to ∼140 K) whereas it turns to hole-like even at x = 0.005 for the Gd-based system. On the basis of the structure of the thermal conductivity hump, and of the electron- or hole-like nature of the thermopower, it has been argued that, in the Y-based system up to x = 0.0075, Mn produces qualitatively the same effect as Gd in the Gd-based system. An analysis of the thermal conductivity data in terms of lattice theory, and the TEP data in terms of a narrow-band picture, has been made to invoke the role of Mn in these systems. Boundary scattering, point defects and sheet-like faults (from κ(T) data analysis) and chemical potential (from S(T) data analysis) support different roles of Mn for x≤0.0075 and x>0.0075.