Half-tapering strategy for conditional simulation with large datasets

Gaussian conditional realizations are routinely used for risk assessment and planning in a variety of Earth sciences applications. Conditional realizations can be obtained by first creating unconditional realizations that are then post-conditioned by kriging. Many efficient algorithms are available for the first step, so the bottleneck resides in the second step. Instead of doing the conditional simulations with the desired covariance (F approach) or with a tapered covariance (T approach), we propose to use the taper covariance only in the conditioning step (Half-Taper or HT approach). This enables to speed up the computations and to reduce memory requirements for the conditioning step but also to keep the right short scale variations in the realizations. A criterion based on mean square error of the simulation is derived to help anticipate the similarity of HT to F. Moreover, an index is used to predict the sparsity of the kriging matrix for the conditioning step. Some guides for the choice of the taper function are discussed. The distributions of a series of 1D, 2D and 3D scalar response functions are compared for F, T and HT approaches. The distributions obtained indicate a much better similarity to F with HT than with T.Comment: 39 pages, 2 Tables and 11 Figure

Controlled absorption and all-optical diode action due to collisions of self-induced transparency solitons

We study inelastic collisions of counter-propagating self-induced transparency solitons in a homogeneously broadened two-level medium. The energy of the pulse can be almost totally absorbed in the medium due to asymmetric collision with a properly chosen control pulse. The medium state thus prepared demonstrates the property of an all-optical diode which transmits pulses from one direction and blocks from another. The saturation process of a controlled absorption effect, local-field correction influence, and the parameter ranges for the diode action are studied as well.Comment: 7 pages, 9 figure

A century of methodological individualism part 2: Mises and Hayek

2009 marks the centenary of methodological individualism (MI). The phrase was first used in English in a 1909 paper by Joseph Schumpeter in the Quarterly Journal of Economics. Yet after 100 years there is considerable confusion as to what the phrase means. MI is often invoked as a fundamental description of the methodology both of neoclassical and Austrian economics, as well as of other approaches, from New Keynesianism to analytical Marxism. However, the methodologies of those to whom the theoretical practice of MI is ascribed differ profoundly on the status of the individual economic agent, some adopting a holistic and some a reductionist standpoint. The purpose of the research of which this paper is part is to uncover and evaluate some of the meanings of the phrase methodological individualism (MI). The first paper in the series, "A Century of Methodological Individualism Part 1: Schumpeter and Menger" (Denis, 2009), considers the contributions of Joseph Schumpeter, who was the first to use the term, and of Carl Menger, considered by many to be the founder of MI. The present paper considers the contributions of von Mises and Hayek. The conclusion drawn is that Mises and Hayek based their methodological stance on fundamentally different ontologies, with von Mises building on the reductionism of previous writers such as Schumpeter and Menger, and Hayek, on the contrary, adopting a holistic ontology more in line with Adam Smith, Marx and Keynes. From an ontological perspective this leaves Hayek as something of an outlier in the Austrian tradition

"Father Joe: the man who saved my soul" by Tony Hendra

Review of Tony Hendra, Father Joe: The Man Who Saved My Soul (London: Penguin Books, 2004)Publisher PD