414 research outputs found
Interaction of free-floating planets with a star-planet pair
The recent discovery of free-floating planets and their theoretical
interpretation as celestial bodies, either condensed independently or ejected
from parent stars in tight clusters, introduced an intriguing possibility.
Namely, that some exoplanets are not condensed from the protoplanetary disk of
their parent star. In this novel scenario a free-floating planet interacts with
an already existing planetary system, created in a tight cluster, and is
captured as a new planet. In the present work we study this interaction process
by integrating trajectories of planet-sized bodies, which encounter a binary
system consisting of a Jupiter-sized planet revolving around a Sun-like star.
To simplify the problem we assume coplanar orbits for the bound and the
free-floating planet and an initially parabolic orbit for the free-floating
planet. By calculating the uncertainty exponent, a quantity that measures the
dependence of the final state of the system on small changes of the initial
conditions, we show that the interaction process is a fractal classical
scattering. The uncertainty exponent is in the range (0.2-0.3) and is a
decreasing function of time. In this way we see that the statistical approach
we follow to tackle the problem is justified. The possible final outcomes of
this interaction are only four, namely flyby, planet exchange, capture or
disruption. We give the probability of each outcome as a function of the
incoming planet's mass. We find that the probability of exchange or capture (in
prograde as well as retrograde orbits and for very long times) is
non-negligible, a fact that might explain the possible future observations of
planetary systems with orbits that are either retrograde or tight and highly
eccentric.Comment: 19 pages, 12 figure
Identifying the neuroretinal rim boundary using dynamic contours
Abstract The neuroretinal rim forms the outer boundary of the optic nerve head: that region of the retina where blood vessels and nerve fibres pass out of the eye. It is normally a circular structure, but is known to change shape due to nerve damage in glaucoma. Its shape can therefore be used in the diagnosis and assessment of the treatment of this disease. Automatically finding the boundary would be useful as it would allow reliable quantitative shape measurements to be made. However, it is a difficult problem as the boundary is ill defined and partially obscured by blood vessels. In this paper we present an algorithm that successfully identifies the boundary using dynamic contours (snakes). The success of the algorithm is very dependent on preprocessing the image to enhance the contrast between the retina and the optic nerve head. We therefore describe the preprocessing in some detail. The algorithm has been tested on numerous images and found to be successful, as judged by an optometrist, in every case.
Exploring the ‘middle ground’ between state and market: the example of China
Studies of housing systems lying in the ‘middle ground’ between state and market are subject to three important shortcomings. First, the widely used Esping-Andersen (EA) approach assesses only a subset of the key housing outcomes and may be less helpful for describing changes in housing policy regimes. Second, there is too much emphasis on tenure transitions, and an assumed close correspondence between tenure labels and effective system functioning may not be valid. Third, due attention has not been given to the spatial dimensions in which housing systems operate, in particular when housing policies have a significant devolved or localised emphasis. Updating EA’s framework, we suggest a preliminary list of housing system indicators in order to capture the nature of the housing systems being developed and devolved. We verified the applicability of this indicator system with the case of China. This illustrates clearly the need for a more nuanced and systematic basis for categorising differences and changes in welfare and housing policies
Mass and Angular Momentum Transfer in the Massive Algol Binary RY Persei
We present an investigation of H-alpha emission line variations observed in
the massive Algol binary, RY Per. We give new radial velocity data for the
secondary based upon our optical spectra and for the primary based upon high
dispersion UV spectra. We present revised orbital elements and an estimate of
the primary's projected rotational velocity (which indicates that the primary
is rotating 7 times faster than synchronous). We use a Doppler tomography
algorithm to reconstruct the individual primary and secondary spectra in the
region of H-alpha, and we subtract the latter from each of our observations to
obtain profiles of the primary and its disk alone. Our H-alpha observations of
RY Per show that the mass gaining primary is surrounded by a persistent but
time variable accretion disk. The profile that is observed outside-of-eclipse
has weak, double-peaked emission flanking a deep central absorption, and we
find that these properties can be reproduced by a disk model that includes the
absorption of photospheric light by the band of the disk seen in projection
against the face of the star. We developed a new method to reconstruct the disk
surface density distribution from the ensemble of H-alpha profiles observed
around the orbit, and this method accounts for the effects of disk occultation
by the stellar components, the obscuration of the primary by the disk, and flux
contributions from optically thick disk elements. The resulting surface density
distribution is elongated along the axis joining the stars, in the same way as
seen in hydrodynamical simulations of gas flows that strike the mass gainer
near trailing edge of the star. This type of gas stream configuration is
optimal for the transfer of angular momentum, and we show that rapid rotation
is found in other Algols that have passed through a similar stage.Comment: 39 pages, 12 figures, ApJ in press, 2004 June 20 issu
Troubling stories of the end of occupy : feminist narratives of betrayal at occupy Glasgow
This article offers a feminist take on the question of why Occupy camps closed down, in the form of a narrative analysis of interviews from participants in Occupy Glasgow. In response to the emergence of an activist discourse emphasising the role of external forces in camp closure and the existence of a longer-term legacy in terms of individual and community politicisation, I build here on feminist interventions that point instead to serious internal problems within the camps and thus to a more limited legacy. Interrogating the plotting, characterisation and denouement of interviewee narratives, I show that feminist participants in Occupy Glasgow characterise the trajectory of the camp as a tragedy, attribute responsibility for the camp’s demise to co-campers and sometimes to themselves, and present the outcome of Occupy Glasgow as limited, and in some cases even traumatic. This raises serious questions about the culmination and outcomes of Occupy in Glasgow and more generally, and indicates the extent of the hard work remaining if future mobilisation against neoliberal austerity is to be more inclusive and sustainable. The article closes by considering the theoretical implications for the wider question of why movements come to an end
Genome-wide association studies and prediction of 17 traits related to phenology, biomass and cell wall composition in the energy grass Miscanthus sinensis
Increasing demands for food and energy require a step change in the effectiveness, speed and flexibility of crop breeding. Therefore, the aim of this study was to assess the potential of genome-wide association studies (GWASs) and genomic selection (i.e. phenotype prediction from a genome-wide set of markers) to guide fundamental plant science and to accelerate breeding in the energy grass Miscanthus. We generated over 100 000 single-nucleotide variants (SNVs) by sequencing restriction site-associated DNA (RAD) tags in 138 Micanthus sinensis genotypes, and related SNVs to phenotypic data for 17 traits measured in a field trial. Confounding by population structure and relatedness was severe in naïve GWAS analyses, but mixed-linear models robustly controlled for these effects and allowed us to detect multiple associations that reached genome-wide significance. Genome-wide prediction accuracies tended to be moderate to high (average of 0.57), but varied dramatically across traits. As expected, predictive abilities increased linearly with the size of the mapping population, but reached a plateau when the number of markers used for prediction exceeded 10 000–20 000, and tended to decline, but remain significant, when cross-validations were performed across subpopulations. Our results suggest that the immediate implementation of genomic selection in Miscanthus breeding programs may be feasible
The difference that tenure makes
This paper argues that housing tenures cannot be reduced to either production relations or consumption relations. Instead, they need to be understood as modes of housing distribution, and as having complex and dynamic relations with social classes. Building on a critique of both the productionist and the consumptionist literature, as well as of formalist accounts of the relations between tenure and class, the paper attempts to lay the foundations for a new theory of housing tenure. In order to do this, a new theory of class is articulated, which is then used to throw new light on the nature of class-tenure relations
- …