6,589 research outputs found
Ultra-compact dwarf galaxies: a new class of compact stellar system discovered in the Fornax Cluster
We have used the 2dF spectrograph on the Anglo-Australian Telescope to obtain
a complete spectroscopic sample of all objects in the magnitude range, Bj= 16.5
to 19.8, regardless of morphology, in an area centred on the Fornax Cluster of
galaxies. Among the unresolved targets are five objects which are members of
the Fornax Cluster. They are extremely compact stellar systems with scale
lengths less than 40 parsecs. These ultra-compact dwarfs are unlike any known
type of stellar system, being more compact and significantly less luminous than
other compact dwarf galaxies, yet much brighter than any globular cluster.Comment: To appear in IAU Symposium 207: Extragalactic Star Cluster
Helium condensation in aerogel: avalanches and disorder-induced phase transition
We present a detailed numerical study of the elementary condensation events
(avalanches) associated to the adsorption of He in silica aerogels. We use
a coarse-grained lattice-gas description and determine the nonequilibrium
behavior of the adsorbed gas within a local mean-field analysis, neglecting
thermal fluctuations and activated processes. We investigate the statistical
properties of the avalanches, such as their number, size and shape along the
adsorption isotherms as a function of gel porosity, temperature, and chemical
potential. Our calculations predict the existence of a line of critical points
in the temperature-porosity diagram where the avalanche size distribution
displays a power-law behavior and the adsorption isotherms have a universal
scaling form. The estimated critical exponents seem compatible with those of
the field-driven Random Field Ising Model at zero temperature.Comment: 16 pages, 14 figure
Long Range Correlation in Granular Shear Flow II: Theoretical Implications
Numerical simulations are used to test the kinetic theory constitutive
relations of inertial granular shear flow. These predictions are shown to be
accurate in the dilute regime, where only binary collisions are relevant, but
underestimate the measured value in the dense regime, where force networks of
size are present. The discrepancy in the dense regime is due to
non-collisional forces that we measure directly in our simulations and arise
from elastic deformations of the force networks. We model the non-collisional
stress by summing over all paths that elastic waves travel through force
networks. This results in an analytical theory that successfully predicts the
stress tensor over the entire inertial regime without any adjustable
parameters
Type and density of independent takeaway outlets: a geographical mapping study in a low socioeconomic ward, Manchester.
OBJECTIVES: The socioeconomic disparity in childhood and early adult obesity prevalence has been well characterised. Takeaway outlets may cluster in lower socioeconomic areas and their proximity to schools is of concern. This study aimed to map takeaway food outlets, characterise takeaway types and their proximity to educational institutions within a low socioeconomic ward in Manchester. DESIGN: The Rusholme ward and a 2 km Euclidean buffer were included as the study area. Local authority Environmental Health data were used to map the takeaway outlets, using QGIS V.2.18.0 (OPENGIS.ch LLC, Einsiedeln, Switzerland). The types of takeaway outlets and major roads were included. Number of outlets within a 400 m Euclidean walking buffer of educational institutions were mapped. SETTING: Rusholme, Manchester, UK. RESULTS: Within the study area, 202 takeaway food outlets were identified and mapped as cluster points. Of these, 62.3% are located on major (A and B) roads, while the remaining outlets were located on minor roads. The majority (57.4%) of takeaway outlets sold similar items (fried chicken, burgers, pizzas, kebabs), with the remainder offering more diverse menus. Of the 53 schools, colleges and universities within the study area, 28 (52.8%) had 1-5 takeaway food outlets within 400 m, 9 (17.0%) had 6-10 outlets; 4 (7.5%) more than 11 outlets with 12 (22.6%) having zero outlets within 400 m. CONCLUSION: Within this low socioeconomic area, there was a high concentration of takeaway food outlets, predominantly along major roads and in easy walking distance of educational establishments with the majority offering similar foods. In addition, a high proportion of these outlets were in easy walking distance of educational establishments. Public health policy needs to consider the implications of current takeaway food outlets and not just the proliferation of these outlets with current planning laws
Shakeouts in Digital Markets: Lessons from B2B Exchanges
Shakeouts loom large in the landscape of all fast-growing markets. During the boom period, an unsustainable glut of competitors is attracted by forecasts of high growth and promises of exceptional returns. Even when the market is already crowded, more entrants keep arriving. These followers are often naïve about the barriers to entry and don\u27t realize how many others are also poised to enter at the same time. Reality intrudes with a bust that precipitates the exit of more than 80 percent of the players through failure or acquisition. This shakeout is triggered by some combination of disappointing growth, pricing pressures that degrade profit prospects, or shortages of crucial people and financial resources
The Fornax Spectroscopic Survey I. Survey Strategy and Preliminary Results on the Redshift Distribution of a Complete Sample of Stars and Galaxies
The Fornax Spectroscopic Survey will use the Two degree Field spectrograph
(2dF) of the Anglo-Australian Telescope to obtain spectra for a complete sample
of all 14000 objects with 16.5<=Bj<=19.7 in a 12 square degree area centred on
the Fornax Cluster. By selecting all objects---both stars and
galaxies---independent of morphology, we cover a much larger range of surface
brightness and scale size than previous surveys. In this paper we present
results from the first 2dF field. Redshift distributions and velocity
structures are shown for all observed objects in the direction of Fornax,
including Galactic stars, galaxies in and around the Fornax Cluster, and for
the background galaxy population. The velocity data for the stars show the
contributions from the different Galactic components, plus a small tail to high
velocities. We find no galaxies in the foreground to the cluster in our 2dF
field. The Fornax Cluster is clearly defined kinematically. The mean velocity
from the 26 cluster members having reliable redshifts is 1560+/-80 km/s. They
show a velocity dispersion of 380+/-50 km/s. Large-scale structure can be
traced behind the cluster to a redshift beyond z=0.3. Background compact
galaxies and low surface brightness galaxies are found to follow the general
galaxy distribution.Comment: LaTeX format; uses aa.cls (included). Accepted for publication in
Astronomy and Astrophysic
Gas adsorption/desorption in silica aerogels: a theoretical study of scattering properties
We present a numerical study of the structural correlations associated to gas
adsorption/desorption in silica aerogels in order to provide a theoretical
interpretation of scattering experiments. Following our earlier work, we use a
coarse-grained lattice-gas description and determine the nonequilibrium
behavior of the adsorbed gas within a local mean-field analysis.
We focus on the differences between the adsorption and desorption mechanisms
and their signature in the fluid-fluid and gel-fluid structure factors as a
function of temperature. At low temperature, but still in the regime where the
isotherms are continuous, we find that the adsorbed fluid density, during both
filling and draining, is correlated over distances that may be much larger than
the gel correlation length. In particular, extended fractal correlations may
occur during desorption, indicating the existence of a ramified cluster of
vapor filled cavities. This also induces an important increase of the
scattering intensity at small wave vectors. The similarity and differences with
the scattering of fluids in other porous solids such as Vycor are discussed.Comment: 16 pages, 15 figure
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