16,209 research outputs found
Hibernation Revived by Weak Magnetic Braking
Cataclysmic variables undergo periodic nova explosions during which a finite
mass of material is expelled on a short timescale. The system widens and, as a
result, the mass-transfer rate drops. This state of hibernation may account for
the variety of cataclysmic variable types observed in systems of similar mass
and period. In the light of recent changes to the theory of nova ignition and
magnetic braking we investigate whether hibernation remains a viable mechanism
for creating cataclysmic variable diversity. We model the ratio of time spent
as dwarf novae (DNe) to nova-like systems (NLs). Above a critical mass-transfer
rate the system is NL and below it a DN. The dominant loss of angular momentum
is by magnetic braking but the rate is uncertain. It is also uncertain what
fraction of the mass accreted is expelled during the novae. We compare the
models of the ratios against the period of the system for different magnetic
braking rates and different ejected masses with the ratio of the number of
observed NLs to DNe. We deduce that a rate of angular momentum loss a factor of
ten smaller than that traditionally assumed is necessary if hibernation is to
account for the observed ratios
Weak Gravitational Lensing and Cluster Mass Estimates
Hierarchical theories of structure formation predict that clusters of
galaxies should be embedded in a web like structure, with filaments emanating
from them to large distances. The amount of mass contained within such
filaments near a cluster can be comparable to the collapsed mass of the cluster
itself. Diffuse infalling material also contains a large amount of mass. Both
these components can contribute to the cluster weak lensing signal. This
``projection bias'' is maximized if a filament lies close to the line-of-sight
to a cluster. Using large--scale numerical simulations of structure formation
in a cosmological constant dominated cold dark matter model, we show that the
projected mass typically exceeds the actual mass by several tens of percent.
This effect is significant for attempts to estimate cluster masses through weak
lensing observations, and will affect weak lensing surveys aimed at
constructing the cluster mass function.Comment: 4 pages, 3 figures. LaTeX2e, uses emulateapj.sty and onecolfloat.sty.
To be submitted to the Astrophysical Journal Letter
Seawater transfer alters the intestinal microbiota profiles of Atlantic salmon (Salmo salar L.)
This study was funded by a BBSRC Eastbio PhD studentship to CED and BBSRC grant BB/M026604/1. The authors wish to thank Ana Rita Sancho Silva for facilitating the sampling for the experiment. Furthermore we would like to express our gratitude to Ian and Alastair Fraser for their support at the SFF fish farms on the Isle of Mull.Peer reviewedPublisher PD
OPEN ACCESS AND MISSING MARKETS IN ARTISANAL FISHING
This paper combines a model of open access fisheries exploitation with a distance-based approach to missing labor and product markets. The model generates predictions about the circumstances under which exploitation increases or decreases with distance. An econometric model is estimated with survey data from artisanal fishing households in Minahasa, Indonesia. The results can be used to assess the impacts of improved transportation infrastructure on fishery exploitation.Marketing,
Optical signatures of quantum delocalization over extended domains in photosynthetic membranes
The prospect of coherent dynamics and excitonic delocalization across several
light-harvesting structures in photosynthetic membranes is of considerable
interest, but challenging to explore experimentally. Here we demonstrate
theoretically that the excitonic delocalization across extended domains
involving several light-harvesting complexes can lead to unambiguous signatures
in the optical response, specifically, linear absorption spectra. We
characterize, under experimentally established conditions of molecular assembly
and protein-induced inhomogeneities, the optical absorption in these arrays
from polarized and unpolarized excitation, and demonstrate that it can be used
as a diagnostic tool to determine the coherent coupling among iso-energetic
light-harvesting structures. The knowledge of these couplings would then
provide further insight into the dynamical properties of transfer, such as
facilitating the accurate determination of F\"orster rates.Comment: 4 figures and Supplementary information with 7 figures. To appear in
Journal of physical chemistry A, 201
Forecasting Seismic Signatures of Stellar Magnetic Activity
For the Sun, a tight correlation between various activity measures and
oscillation frequencies is well documented. For other stars, we have abundant
data on magnetic activity and its changes but not yet on its seismic signature.
A prediction of the activity induced frequency changes in stars based on
scaling the solar relations is presented. This seismic signature of the
activity should be measurable in the data expected within few years.Comment: 8 pages, 3 figures, to appear in proceedings of "Unsolved Problems in
Stellar Physics" conference (Cambridge, UK, July 2007
Mass loss and supernova progenitors
We first discuss the mass range of type IIP SN progenitors and how the upper
and lower limits impose interesting constraints on stellar evolution. Then we
discuss the possible implications of two SNe, 2002ap and 2006jc, for Wolf-Rayet
star mass-loss rates and long Gamma-ray bursts.Comment: 7 pages, 3 figures, to appear in the Conference Proceedings of
"Unsolved Problems in Stellar Astrophysics
The coupling between pulsation and mass loss in massive stars
To what extent can pulsational instabilities resolve the mass-loss problem of
massive stars? How important is pulsation in structuring and modulating the
winds of these stars? What role does pulsation play in redistributing angular
momentum in massive stars? Although I cannot offer answers to these questions,
I hope at the very least to explain how they come to be asked.Comment: 12 pages, 1 figure, to appear in proceedings of "Unsolved Problems in
Stellar Physics" conference (Cambridge, UK, July 2007
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