Homological realization of prescribed abelian groups via KK-theory

Using algebraic and topological K-theory together with complex C^*-algebras, we prove that every abelian group may be realized as the centre of a strongly torsion generated group whose integral homology is zero in dimension one and isomorphic to two arbitrarily prescribed abelian groups in dimensions two and three.Comment: 10 page

Homological realization of prescribed abelian groups via K-theory

Using algebraic and topological K-theory together with complex C*-algebras, we prove that every abelian group may be realized as the centre of a strongly torsion generated group whose integral homology is zero in dimension one and isomorphic to two arbitrarily prescribed abelian groups in dimensions two and thre

On the origin of bimodal duration distribution of Gamma Ray Bursts

The modified version of a bullet model for gamma ray bursts is studied. The central engine of the source produces multiple sub-jets that are contained within a cone. The emission of photons in the source frame of a sub-jet either takes part in an infinitesimally thin shell, or during its expansion for a finite time. The analysis of the observed profiles of GRBs taken by BATSE leads us to the conclusion that the latter possibility is much more favored. We also study the statistical distribution of GRBs, in the context of their bimodality of durations, taking into account the detector's capability of observing the signal above a certain flux limit. The model with shells emitting for a finite time is able to reproduce only one class of bursts, short or long, depending on the adopted physical parameters. Therefore we suggest that the GRB bimodality is intrinsically connected with two separate classes of sources.Comment: 12 pages, 12 figures; accepted by MNRAS. Small changes to match the corre cted proof

Observation of Three-dimensional Long-range Order in Smaller Ion Coulomb Crystals in an rf Trap

Three-dimensional long-range ordered structures in smaller and near-spherically symmetric Coulomb crystals of ^{40}Ca^+ ions confined in a linear rf Paul trap have been observed when the number of ions exceeds ~1000 ions. This result is unexpected from ground state molecular dynamics (MD) simulations, but found to be in agreement with MD simulations of metastable ion configurations. Previously, three-dimensional long-range ordered structures have only been reported in Penning traps in systems of ~50,000 ions or more.Comment: 5 pages; 4 figures; to appear in Phys. Rev. Lett.; changed content

Events in the affective city: Affect, attention and alignment in two ordinary urban events

In a representational regime, planned urban events are used by urban planners to render urban projects visible and acceptable. As a corollary of the focus of urban studies on their representational dimension and in spite of a burgeoning literature on the notion of affective urbanism, the experiential character of events remains surprisingly unexplored. This paper argues that an ordinary regime of events is mobilised by city-makers to act on the embodied, affective experience of the city and on the ways urban dwellers know and act upon the city. By analysing planned urban events in their embodied, experiential dimension, we focus on the ways in which, through the design of ephemeral material dispositives, urbanists attempt to encourage citizens to incorporate ways of knowing and acting on space and on the modalities of knowing and acting that are at play. We stage an encounter between critical event studies and Ingoldian approaches to affect and attention, examining two urban events in a Swiss canton. We show how intense encounters with urban matter are staged in an attempt to modulate affects, guide attention, and produce alignment with a specific political project, asking urban dwellers either to embody a project still in the making or to cultivate expectations regarding an already-written future

Morphology of the tropopause layer and lower stratosphere above a tropical cyclone : a case study on cyclone Davina (1999)

During the APE-THESEO mission in the Indian Ocean the Myasishchev Design Bureau stratospheric research aircraft M55 Geophysica performed a flight over and within the inner core region of tropical cyclone Davina. Measurements of total water, water vapour, temperature, aerosol backscattering, ozone and tracers were made and are discussed here in comparison with the averages of those quantities acquired during the campaign time frame. Temperature anomalies in the tropical tropopause layer (TTL), warmer than average in the lower part and colder than average in the upper TTL were observed. Ozone was strongly reduced compared to its average value, and thick cirrus decks were present up to the cold point, sometimes topped by a layer of very dry air. Evidence for meridional transport of trace gases in the stratosphere above the cyclone was observed and perturbed water distribution in the TTL was documented. The paper discuss possible processes of dehydration induced by the cirrus forming above the cyclone, and change in the chemical tracer and water distribution in the lower stratosphere 400–430 K due to meridional transport from the mid-latitudes and link with Davina. Moreover it compares the data prior and after the cyclone passage to discuss its actual impact on the atmospheric chemistry and thermodynamics