Atom-optics hologram in the time domain

The temporal evolution of an atomic wave packet interacting with object and reference electromagnetic waves is investigated beyond the weak perturbation of the initial state. It is shown that the diffraction of an ultracold atomic beam by the inhomogeneous laser field can be interpreted as if the beam passes through a three-dimensional hologram, whose thickness is proportional to the interaction time. It is found that the diffraction efficiency of such a hologram may reach 100% and is determined by the duration of laser pulses. On this basis a method for reconstruction of the object image with matter waves is offered.Comment: RevTeX, 13 pages, 8 figures; minor grammatical change

Constraining the Power Spectrum using Clusters

(Shortened Abstract). We analyze a redshift sample of Abell/ACO clusters and compare them with numerical simulations based on the truncated Zel'dovich approximation (TZA), for a list of eleven dark matter (DM) models. For each model we run several realizations, on which we estimate cosmic variance effects. We analyse correlation statistics, the probability density function, and supercluster properties from percolation analysis. As a general result, we find that the distribution of galaxy clusters provides a constraint only on the shape of the power spectrum, but not on its amplitude: a shape parameter 0.18 < \Gamma < 0.25 and an effective spectral index at 20Mpc/h in the range [-1.1,-0.9] are required by the Abell/ACO data. In order to obtain complementary constraints on the spectrum amplitude, we consider the cluster abundance as estimated using the Press--Schechter approach, whose reliability is explicitly tested against N--body simulations. We conclude that, of the cosmological models considered here, the only viable models are either Cold+Hot DM ones with \Omega_\nu = [0.2-0.3], better if shared between two massive neutrinos, and flat low-density CDM models with \Omega_0 = [0.3-0.5].Comment: 37 pages, Latex file, 9 figures; New Astronomy, in pres

The product of a Petrine circle? A reassessment of the origin and character of 1 Peter

© 2002 SAGE PublicationsRecent studies of 1 Peter, especially by John Elliott, have sought to rescue the letter from its assimilation to the Pauline tradition and to establish the view, now widely held, that 1 Peter is the distinctive product of a Petrine circle. After examining the traditions in 1 Peter, both Pauline and non-Pauline, and the names in the letter (Silvanus, Mark and Peter), this essay argues that there is no substantial evidence, either inside or outside the letter, to support the view of 1 Peter as originating from a specifically Petrine group. It is much more plausibly seen as reflecting the consolidation of early Christian traditions in Roman Christianity. Despite the scholarly majority currently in its favour, the view of 1 Peter as the distinctive product of a Petrine tradition from a Petrine circle should therefore be rejected

Rbf Neural Networks With Centers Assignment Via Karhunen-loeve Transform

A technique for assigning the gaussian centers to a Radial Basis Function Neural Network (RBFNN), based on the Karhunen-Loeve Transform (KLT), is proposed. By applying this technique to time series prediction, a significant performance improvement is obtained in comparison with usual prediction methods that use RBFNNs. For instance, by assigning the KLT scaled eigenvectors to the RBFNN centers yields lower prediction normalized mean squared error (NMSE) and requires less previous known samples than the usual technique that applies the own training set vectors to the centers. The present technique has also shown improved performance when compared with prediction based on RBFNNs that uses the K-means clustering algorithm.21265127