Quasi-periodic solutions of completely resonant forced wave equations

We prove existence of quasi-periodic solutions with two frequencies of completely resonant, periodically forced nonlinear wave equations with periodic spatial boundary conditions. We consider both the cases the forcing frequency is: (Case A) a rational number and (Case B) an irrational number.Comment: 25 pages, 1 figur

Phase separation in quasi incompressible fluids: Cahn-Hilliard model in the Cattaneo-Maxwell framework

In this paper we propose a mathematical model of phase separation for a quasi-incompressible binary mixture where the spinodal decomposition is induced by an heat flux governed by the Cattaneo-Maxwell equation. As usual, the phase separation is considered in the framework of phase field modeling so that the transition is described by an additional field, the concentration c. The evolution of concentration is described by the Cahn-Hilliard equation and in our model is coupled with the Navier-Stokes equation. Since thermal effect are included, the whole set of evolution equations is set up for the velocity, the concentration, the temperature and the heat flux. The model is compatible with thermodynamics and a maximum theorem holds.Comment: Submitted to ZAM

Eccentricity content of binary black hole initial data

Using a post-Newtonian diagnostic tool developed by Mora and Will, we examine numerically generated quasiequilibrium initial data sets that have been used in recently successful numerical evolutions of binary black holes through plunge, merger and ringdown. We show that a small but significant orbital eccentricity is required to match post-Newtonian and quasiequilibrium calculations. If this proves to be a real eccentricity, it could affect the fine details of the subsequent numerical evolutions and the predicted gravitational waveforms.Comment: 5 pages, 5 figures, clarifications and minor corrections; version submitted to Phys. Rev.

Considerations on the excitation of black hole quasinormal modes

We provide some considerations on the excitation of black hole quasinormal modes (QNMs) in different physical scenarios. Considering a simple model in which a stream of particles accretes onto a black hole, we show that resonant QNM excitation by hyperaccretion requires a significant amount of fine-tuning, and is quite unlikely to occur in nature. Then we summarize and discuss present estimates of black hole QNM excitation from gravitational collapse, distorted black holes and head-on black hole collisions. We emphasize the areas that, in our opinion, are in urgent need of further investigation from the point of view of gravitational wave source modeling.Comment: 11 pages, 2 figures, proceedings of the 7th International Conference of the Hellenic Astronomical Society. Complements section VB of gr-qc/051216

Liquid spirits : the (re)production of academic identities through practices

University of Technology Sydney. Faculty of Business.Business schools have important social, economic and moral responsibilities, since their teaching and research influence managerial and entrepreneurial practices. A rich debate surrounds the characteristics and limitations of the current model of business education as well as what should be done now and in the future to create better managers and entrepreneurs. The intent of this research is to offer an original contribution to this discussion by investigating the factors that shape the behaviour of management academics. Business Schools seek to capture not only the best knowledge, research and teaching in their ranks but also to direct it towards goal-oriented corporate purposes, whether in the pursuit of accreditation, rankings, or some other measure of ‘excellence’. In doing so, they necessarily seek to shape and frame the activities, choices and performances of management academics. Some pertinent questions that arise in regards to their doing so are the following: are the behaviours of management and business school academics primarily shaped by their individual agency, by the managerial efforts of the organizations in which they are embedded or by other forces? What can be done to enhance collaboration or direct individual efforts towards specific goals? By addressing these questions, my thesis problematizes some assumptions that are implicit in the current debate, to which I propose alternatives. The research adopts two theoretical lenses to pursue this objective, practice theory and social identity theory. These theories are used to interpret data on narrative accounts of professional identities and on the working practices of a group of management academics that operate in the context of a transforming business school. The sources of data include 72 questionnaires, 16 semi-structured interviews, as well as two years of ethnographic field observations. This ‘micro’ analysis is situated in the context of a large spectrum critical analysis of the discursive landscape in which academic work is performed. This includes both a ‘mapping’ of the global Discourses of business education and of academic work (performed through a genealogic discourse analysis of the literature) and an examination of the local discourses characterizing the specific workplace of my informants. By combining these multiple sources of information, this work depicts a representation of the life-world of management academics, one that includes social, technological, political, organizational and emotional forces. My findings demonstrate that the relationship between academic identities and practices is situated in a liminal space characterized by exposure to a variety of material, discursive and relational tensions. I suggest this induces liquefaction of academic identities, which I describe as ‘liquid spirits’. As such, they are resistant to direct managerial supervision but remain ‘bottled up’ in facilitative circuits of power. In conclusion I suggest that, in order to ‘organize’ management academics’ efforts productively, it is necessary to take this complexity into account and I offer some concrete example of possible (albeit not uncontroversial) alternatives to facilitate academic work

Estimating spinning binary parameters and testing alternative theories of gravity with LISA

We investigate the effect of spin-orbit and spin-spin couplings on the estimation of parameters for inspiralling compact binaries of massive black holes, and for neutron stars inspiralling into intermediate-mass black holes, using hypothetical data from the proposed Laser Interferometer Space Antenna (LISA). We work both in Einstein's theory and in alternative theories of gravity of the scalar-tensor and massive-graviton types. We restrict the analysis to non-precessing spinning binaries, i.e. to cases where the spins are aligned normal to the orbital plane. We find that the accuracy with which intrinsic binary parameters such as chirp mass and reduced mass can be estimated within general relativity is degraded by between one and two orders of magnitude. We find that the bound on the coupling parameter omega_BD of scalar-tensor gravity is significantly reduced by the presence of spin couplings, while the reduction in the graviton-mass bound is milder. Using fast Monte-Carlo simulations of 10^4 binaries, we show that inclusion of spin terms in massive black-hole binaries has little effect on the angular resolution or on distance determination accuracy. For stellar mass inspirals into intermediate-mass black holes, the angular resolution and the distance are determined only poorly, in all cases considered. We also show that, if LISA's low-frequency noise sensitivity can be extrapolated from 10^-4 Hz to as low as 10^-5 Hz, the accuracy of determining both extrinsic parameters (distance, sky location) and intrinsic parameters (chirp mass, reduced mass) of massive binaries may be greatly improved.Comment: 29 pages, 9 figures. Matches version accepted in Physical Review D. More stringent checks in the inversion of the Fisher matri

Quasi-T\"oplitz functions in KAM theorem

We define and describe the class of Quasi-T\"oplitz functions. We then prove an abstract KAM theorem where the perturbation is in this class. We apply this theorem to a Non-Linear-Scr\"odinger equation on the torus $T^d$, thus proving existence and stability of quasi-periodic solutions and recovering the results of [10]. With respect to that paper we consider only the NLS which preserves the total Momentum and exploit this conserved quantity in order to simplify our treatment.Comment: 34 pages, 1 figur

Turbulence and coarsening in active and passive binary mixtures

Phase separation between two fluids in two-dimensions is investigated by means of Direct Numerical Simulations of coupled Navier-Stokes and Cahn-Hilliard equations. We study the phase ordering process in the presence of an external stirring acting on the velocity field. For both active and passive mixtures we find that, for a sufficiently strong stirring, coarsening is arrested in a stationary dynamical state characterized by a continuous rupture and formation of finite domains. Coarsening arrest is shown to be independent of the chaotic or regular nature of the flow.Comment: 4 pages, 5 figures; discussion on the dependence of the arrest scale on the shear rate has been added; figures have been modified accordingl