137 research outputs found
On the multiplicity of the O-star Cyg OB2 #8A and its contribution to the gamma-ray source 3EG J2033+4118
We present the results of an intensive spectroscopic campaign in the optical
waveband revealing that Cyg OB2 #8A is an O6 + O5.5 binary system with a period
of about 21.9 d. Cyg OB2 #8A is a bright X-ray source, as well as a non-thermal
radio emitter. We discuss the binarity of this star in the framework of a
campaign devoted to the study of non-thermal emitters, from the radio waveband
to gamma-rays. In this context, we attribute the non-thermal radio emission
from this star to a population of relativistic electrons, accelerated by the
shock of the wind-wind collision. These relativistic electrons could also be
responsible for a putative gamma-ray emission through inverse Compton
scattering of photospheric UV photons, thus contributing to the yet
unidentified EGRET source 3EG J2033+4118.Comment: 8 pages, 4 figures, conference on "The Multiwavelength Approach to
Gamma-Ray Sources", to appear in Ap&S
Electrical transport studies of quench condensed Bi films at the initial stage of film growth: Structural transition and the possible formation of electron droplets
The electrical transport properties of amorphous Bi films prepared by
sequential quench deposition have been studied in situ. A
superconductor-insulator (S-I) transition was observed as the film was made
increasingly thicker, consistent with previous studies. Unexpected behavior was
found at the initial stage of film growth, a regime not explored in detail
prior to the present work. As the temperature was lowered, a positive
temperature coefficient of resistance (dR/dT > 0) emerged, with the resistance
reaching a minimum before the dR/dT became negative again. This behavior was
accompanied by a non-linear and asymmetric I-V characteristic. As the film
became thicker, conventional variable-range hopping (VRH) was recovered. We
attribute the observed crossover in the electrical transport properties to an
amorphous to granular structural transition. The positive dR/dT found in the
amorphous phase of Bi formed at the initial stage of film growth was
qualitatively explained by the formation of metallic droplets within the
electron glass.Comment: 7 pages, 6 figure
Coulomb gap in a model with finite charge transfer energy
The Coulomb gap in a donor-acceptor model with finite charge transfer energy
describing the electronic system on the dielectric side of the
metal-insulator transition is investigated by means of computer simulations on
two- and three-dimensional finite samples with a random distribution of equal
amounts of donor and acceptor sites. Rigorous relations reflecting the symmetry
of the model presented with respect to the exchange of donors and acceptors are
derived. In the immediate neighborhood of the Fermi energy the the
density of one-electron excitations is determined solely by
finite size effects and further away from is described by
an asymmetric power law with a non-universal exponent, depending on the
parameter .Comment: 10 pages, 6 figures, submitted to Phys. Rev.
Fertility, Living Arrangements, Care and Mobility
There are four main interconnecting themes around which the contributions in this book are based. This introductory chapter aims to establish the broad context for the chapters that follow by discussing each of the themes. It does so by setting these themes within the overarching demographic challenge of the twenty-first century – demographic ageing. Each chapter is introduced in the context of the specific theme to which it primarily relates and there is a summary of the data sets used by the contributors to illustrate the wide range of cross-sectional and longitudinal data analysed
Immigration and Internal Migration 'Flight' from US Metropolitan Areas: Toward a New Demographic Balkanisation
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68704/2/10.1080_00420989550012861.pd
Cosmological Constraints on Decaying Dark Matter
We present a complete analysis of the cosmological constraints on decaying
dark matter. Previous analyses have used the cosmic microwave background and
Type Ia supernova. We have updated them with the latest data as well as
extended the analysis with the inclusion of Lyman- forest, large scale
structure and weak lensing observations. Astrophysical constraints are not
considered in the present paper. The bounds on the lifetime of decaying dark
matter are dominated by either the late-time integrated Sachs-Wolfe effect for
the scenario with weak reionization, or CMB polarization observations when
there is significant reionization. For the respective scenarios, the lifetimes
for decaying dark matter are Gyr and Gyr (at 95.4% confidence level), where the
phenomenological parameter is the fraction of the decay energy deposited in
baryonic gas. This allows us to constrain particle physics models with dark
matter candidates through investigation of dark matter decays into Standard
Model particles via effective operators. For decaying dark matter of
GeV mass, we found that the size of the coupling constant in the effective
dimension-4 operators responsible for dark matter decay has to generically be . We have also explored the implications of our analysis for
representative models in theories of gauge-mediated supersymmetry breaking,
minimal supergravity and little Higgs.Comment: 29 pages, 6 figures. Added references and corrected typos as well as
grammatical oversight
Contingent self-definition and amorphous regions: a dynamic approach to place brand architecture
This article explores the concept of contingent self-definition, whereby place brands employ flexible self-definitional approaches in constructing their place brand architecture. Adopting a view of regions as social constructs, the article builds on and extends previous work on place brand architecture by identifying the underlying factors that drive contingent self-definition decisions. Based on an empirical study of professionals tasked with managing region brands in the Netherlands, eleven factors are identified as drivers of contingent self-definition by place brands. These factors are grouped into four thematic categories: i) external perceptions, ii) proximity, iii) brand relationships, and iv) politics and power. A dynamic approach to place brand architecture is advocated, foregrounding the amorphous character of regions as social constructs that defy reification solely as fixed territorial-administrative spaces
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