Stone's theorem for strongly continuous groups of isometries in Hardy spaces

AbstractFor 1 < p < ∞, p ≠ 2, it is well known that a strongly continuous, one-parameter group of isometries in the Hardy space Hp(D) does not satisfy the classical Stone theorem, that is, there is no σ-additive spectral measure on the Borel sets of the real line whose Fourier-Stieltjes transform is the given group. However, if we relax the topology of Hp(D) by imbedding it into some larger space, then it is shown, for the case of 1 < p < 2, that any such group does satisfy Stone's theorem when considered as acting in some appropriate larger space. The situation for 2 < p < ∞ is more complicated. If the group of isometries is of elliptic type then it again satisfies Stone's theorem in a suitable larger space. However, for parabolic groups the situation is fundamentally different; such a group can never be interpreted as a Fourier-Stieltjes transform in any space containing Hp(D)

An orientable, stabilized balloon-borne gondola for around-the-world flights

A system capable of pointing a balloon-borne telescope at selected celestial objects to an accuracy of approximately 10 arc minutes for an extended period (weeks to months) without reliance on telemetry is described. A unique combination of a sun/star tracker, an on-board computer, and a gyrocompass is utilized for navigation, source acquisition and tracking, and data compression and recording. The possibilities for intelligent activities by the computer are also discussed

Robust Emergent Activity in Dynamical Networks

We study the evolution of a random weighted network with complex nonlinear dynamics at each node, whose activity may cease as a result of interactions with other nodes. Starting from a knowledge of the micro-level behaviour at each node, we develop a macroscopic description of the system in terms of the statistical features of the subnetwork of active nodes. We find the asymptotic characteristics of this subnetwork to be remarkably robust: the size of the active set is independent of the total number of nodes in the network, and the average degree of the active nodes is independent of both the network size and its connectivity. These results suggest that very different networks evolve to active subnetworks with the same characteristic features. This has strong implications for dynamical networks observed in the natural world, notably the existence of a characteristic range of links per species across ecological systems.Comment: 4 pages, 5 figure

Rapid fluctuations in the high-energy X-ray flux from a source in Crux

Balloonborne X ray telescopic observations of two point sources in Cru

Report of the x ray and gamma ray sensors panel

Overall five major areas of technology are recommended for development in order to meet the science requirements of the Astrotech 21 mission set. These are: detectors for high resolution gamma ray spectroscopy, cryogenic detectors for improved x ray spectral and spatial resolution, advanced x ray charge coupled devices (CCDs) for higher energy resolution and larger format, extension to higher energies, liquid and solid position sensitive detectors for improving stopping power in the energy range 5 to 500 keV and 0.2 to 2 MeV. Development plans designed to achieve the desired capabilities on the time scales required by the technology freeze dates have been recommended in each of these areas

Transiting Exoplanet Survey Satellite (TESS)

The Transiting Exoplanet Survey Satellite (TESS ) will search for planets transiting bright and nearby stars. TESS has been selected by NASA for launch in 2017 as an Astrophysics Explorer mission. The spacecraft will be placed into a highly elliptical 13.7-day orbit around the Earth. During its two-year mission, TESS will employ four wide-field optical CCD cameras to monitor at least 200,000 main-sequence dwarf stars with I_C (approximately less than) 13 for temporary drops in brightness caused by planetary transits. Each star will be observed for an interval ranging from one month to one year, depending mainly on the star's ecliptic latitude. The longest observing intervals will be for stars near the ecliptic poles, which are the optimal locations for follow-up observations with the James Webb Space Telescope. Brightness measurements of preselected target stars will be recorded every 2 min, and full frame images will be recorded every 30 min. TESS stars will be 10-100 times brighter than those surveyed by the pioneering Kepler mission. This will make TESS planets easier to characterize with follow-up observations. TESS is expected to find more than a thousand planets smaller than Neptune, including dozens that are comparable in size to the Earth. Public data releases will occur every four months, inviting immediate community-wide efforts to study the new planets. The TESS legacy will be a catalog of the nearest and brightest stars hosting transiting planets, which will endure as highly favorable targets for detailed investigations

Establishing Performance Standards and Setting Cut-Scores

This article serves as an introduction to the following four articles in which four methods for establishing standards and setting cut-scores are presented and evaluated. The purposes, nature, and characteristics of performance standards are first reviewed. This is followed by a brief discussion of the methods for setting cut-scores. Berk’s (1986) criteria for evaluating four of these procedures are then presented and described.Cet article sert d’introduction aux quatre articles suivants dans lesquels sont présentées et évaluées quatre méthodes pour établir des normes et des seuils de passage. Dans un premier temps, les objectifs, la nature et les caractéristiques des normes de rendement sont examinés. Ensuite, on offre un survol des méthodes employées pour déterminer les seuils de passage. En dernier lieu, on présente et décrit les critères de Berk (1986) pour évaluer quatre de ces procédures