Scalar functions for wave extraction in numerical relativity

Wave extraction plays a fundamental role in the binary black hole simulations currently performed in numerical relativity. Having a well defined procedure for wave extraction, which matches simplicity with efficiency, is critical especially when comparing waveforms from different simulations. Recently, progress has been made in defining a general technique which uses Weyl scalars to extract the gravitational wave signal, through the introduction of the {\it quasi-Kinnersley tetrad}. This procedure has been used successfully in current numerical simulations; however, it involves complicated calculations. The work in this paper simplifies the procedure by showing that the choice of the {\it quasi-Kinnersley tetrad} is reduced to the choice of the time-like vector used to create it. The space-like vectors needed to complete the tetrad are then easily identified, and it is possible to write the expression for the Weyl scalars in the right tetrad, as simple functions of the electric and magnetic parts of the Weyl tensor.Comment: 5 page

Newman-Penrose quantities as valuable tools in astrophysical relativity

In this talk I will briefly outline work in progress in two different contexts in astrophysical relativity, i.e. the study of rotating star spacetimes and the problem of reliably extracting gravitational wave templates in numerical relativity. In both cases the use of Weyl scalars and curvature invariants helps to clarify important issues.Comment: 3 pages. Proceedings of 16th SIGRAV conference, Vietri, Italy, September 200

Jacob Viner’s Reminiscences from the New Deal (February 11, 1953)

This paper presents and reproduces an unpublished oral history interview given by Jacob Viner in 1953. The interview released by Viner for the Columbia Oral History Project gives us a valuable opportunity to throw light on his advisory activity during the New Deal Era. In our introduction we attempt to make a critical appraisal of Viner's reminiscences and to state the contribution they can provide to our general knowledge of the period. In addition, we also attempt to find out some biographical and interpretative elements useful to understand Viner’s own vision and his contribution to important economic policy processes during the New Deal.

Towards a novel wave-extraction method for numerical relativity

We present the recent results of a research project aimed at constructing a robust wave extraction technique for numerical relativity. Our procedure makes use of Weyl scalars to achieve wave extraction. It is well known that, with a correct choice of null tetrad, Weyl scalars are directly associated to physical properties of the space-time under analysis in some well understood way. In particular it is possible to associate $\Psi_4$ with the outgoing gravitational radiation degrees of freedom, thus making it a promising tool for numerical wave--extraction. The right choice of the tetrad is, however, the problem to be addressed. We have made progress towards identifying a general procedure for choosing this tetrad, by looking at transverse tetrads where $\Psi_1=\Psi_3=0$. As a direct application of these concepts, we present a numerical study of the evolution of a non-linearly disturbed black hole described by the Bondi--Sachs metric. This particular scenario allows us to compare the results coming from Weyl scalars with the results coming from the news function which, in this particular case, is directly associated with the radiative degrees of freedom. We show that, if we did not take particular care in choosing the right tetrad, we would end up with incorrect results.Comment: 6 pages, 1 figure, to appear in the Proceedings of the Albert Einstein Century International Conference, Paris, France, 200

Harvard meets the crisis: U.S. fiscal policy in the 1930s and the political economy of Lauchlin B. Currie, Jacob Viner, John H. Williams and Harry D. White

The paper aims to describe the contribution of four Harvard economists to the interpretation of the Great Depression and the policy decision making from 1933 to 1938. Lauchlin B. Currie, Jacob Viner, John H. Williams, Harry D. White, eminent scholars in the field of monetary and international economics, were deeply involved in policy decisions during the New Deal. In our synoptic analysis we will benefit from extensive scholarly work that has been provided in the last few years. We shall examine the extensive biographical connection between Currie, Viner, White and Williams with special regard to their common training at Harvard. Then we shall compare their interpretations of the causes of crisis and their proposals in fiscal, monetary and banking policy. Finally, we shall describe their advisory activity in the Roosevelt administration and try to assess their influence.Great Depression; Monetary Theory; Monetary Policy; Fiscal Policy, Keynesism

Towards a novel wave-extraction method for numerical relativity. I. Foundations and initial-value formulation

The Teukolsky formalism of black hole perturbation theory describes weak gravitational radiation generated by a mildly dynamical hole near equilibrium. A particular null tetrad of the background Kerr geometry, due to Kinnersley, plays a singularly important role within this formalism. In order to apply the rich physical intuition of Teukolsky's approach to the results of fully non-linear numerical simulations, one must approximate this Kinnersley tetrad using raw numerical data, with no a priori knowledge of a background. This paper addresses this issue by identifying the directions of the tetrad fields in a quasi-Kinnersley frame. This frame provides a unique, analytic extension of Kinnersley's definition for the Kerr geometry to a much broader class of space-times including not only arbitrary perturbations, but also many examples which differ non-perturbatively from Kerr. This paper establishes concrete limits delineating this class and outlines a scheme to calculate the quasi-Kinnersley frame in numerical codes based on the initial-value formulation of geometrodynamics.Comment: 11 pages, 1 figur

Intertextuality and Parody of Law in The Third Policeman by Flann O’Brien: a Literary and a Linguistic Reading

This essay aims to provide a dual reading of Flann O’Brien’s novel The Third Policeman: a literary one, centred on the multifarious references to famous works by authors such as Sterne, Gide, Dostoevsky and Kafka, and a linguistic one, in which the intertextual game is sought in the language of legal texts, particularly those belonging to the Irish tradition. While Patrizia Nerozzi explores the interplay with literary genres, motifs and narrative patterns, Mara Logaldo’s analysis identifies wordplays and other recurring rhetorical strategies, focusing on the typical traits of Irish and Legal English. Both studies concentrate on the parody of law that permeates the text: while the literary reading highlights the complex declinations of nonsense within this novel vis-à-vis other literary texts, the linguistic analysis shows to what extent Flann O’Brien exploits the idiosyncrasies of legal language to build up, with words, his architecture of absurdity, his fable of law

Black holes in a box: towards the numerical evolution of black holes in AdS

The evolution of black holes in "confining boxes" is interesting for a number of reasons, particularly because it mimics the global structure of Anti-de Sitter geometries. These are non-globally hyperbolic space-times and the Cauchy problem may only be well defined if the initial data is supplemented by boundary conditions at the time-like conformal boundary. Here, we explore the active role that boundary conditions play in the evolution of a bulk black hole system, by imprisoning a black hole binary in a box with mirror-like boundary conditions. We are able to follow the post-merger dynamics for up to two reflections off the boundary of the gravitational radiation produced in the merger. We estimate that about 15% of the radiation energy is absorbed by the black hole per interaction, whereas transfer of angular momentum from the radiation to the black hole is only observed in the first interaction. We discuss the possible role of superradiant scattering for this result. Unlike the studies with outgoing boundary conditions, both the Newman-Penrose scalars \Psi_4 and \Psi_0 are non-trivial in our setup, and we show that the numerical data verifies the expected relations between them.Comment: REvTex4, 17 pages, 12 Figs. v2: Minor improvements. Published version. Animation of a black hole binary in a box can be found at http://blackholes.ist.utl.pt