Efficient computation of the gravitational wave spectrum emitted by eccentric massive black hole binaries in stellar environments

We present a fast and versatile method to calculate the characteristic spectrum $h_c$ of the gravitational wave background (GWB) emitted by a population of eccentric massive black hole binaries (MBHBs). We fit the spectrum of a reference MBHB with a simple analytic function and show that the spectrum of any other MBHB can be derived from this reference spectrum via simple scalings of mass, redshift and frequency. We then apply our calculation to a realistic population of MBHBs evolving via 3-body scattering of stars in galactic nuclei. We demonstrate that our analytic prescription satisfactorily describes the signal in the frequency band relevant to pulsar timing array (PTA) observations. Finally we model the high frequency steepening of the GWB to provide a complete description of the features characterizing the spectrum. For typical stellar distributions observed in massive galaxies, our calculation shows that 3-body scattering alone is unlikely to affect the GWB in the PTA band and a low frequency turnover in the spectrum is caused primarily by high eccentricities.Comment: 12 pages, 9 figures, published in MNRA

Numerical Investigation of Wind Turbine Airfoils under Clean and Dusty Air Conditions

The focus of research in this thesis is on numerical simulation of airflow around wind turbine airfoils (S809, S814 and S1210) under both clean and dusty air conditions by using Computational Fluid Dynamics (CFD). The physical geometries of the airfoils and the meshing processes are completed in the ANSYS Mesh package ICEM. The simulations and post-processing are done by ANSYS FLUENT. For cases of clean air condition, Spalart–Allmaras (SA), realizable k-ε and Wray-Agarwal (WA) turbulence models are employed in the calculations. The results are compared with the experimental data for validation. For dusty air condition, simulation of the two-phase flow is conducted using the discrete phase model (DPM) for various concentrations of dust particles using the realizable k-ε model and WA turbulence models. The results are compared with the clean air simulations to illustrate the effect of dust contamination on the aerodynamic performance of the airfoils. Finally, some conclusions are drawn on how several factors influence the aerodynamic performance of the airfoils and suggestions are made to improve the wind energy conversion efficiency of airfoils under clean and dusty air conditions

Tailoring Accelerating Beams in Phase Space

An appropriate design of wavefront will enable light fields propagating along arbitrary trajectories thus forming accelerating beams in free space. Previous ways of designing such accelerating beams mainly rely on caustic methods, which start from diffraction integrals and only deal with two-dimensional fields. Here we introduce a new perspective to construct accelerating beams in phase space by designing the corresponding Wigner distribution function (WDF). We find such a WDF-based method is capable of providing both the initial field distribution and the angular spectrum in need by projecting the WDF into the real space and the Fourier space respectively. Moreover, this approach applies to the construction of both two- and three-dimensional fields, greatly generalizing previous caustic methods. It may therefore open up a new route to construct highly-tailored accelerating beams and facilitate applications ranging from particle manipulation and trapping to optical routing as well as material processing.Comment: 8 pages, 6 figure

Studies towards the total synthesis of spiroquinazoline

2007 Summer.Includes bibliographical references.Presented herein is the synthesis of a key intermediate in the total synthesis of spiroquinazoline. By using N-Boc-serine as starting material, an efficient methodology has been developed to synthesize two types of δ,γ-unsaturated-α-amino acids bearing substitution at either the δ- or γ-position. After this, a novel SN2' reaction which introduces two quaternary centers has been developed. The quinazolinone core of the molecular has been constructed. The progress we made in those key steps paves the way to the first total synthesis of spiroquinazoline