29,696 research outputs found
The tasks and roles of social workers: a focused overview of research evidence
Options for Excellence is a joint DfES and DH-funded review of the social care workforce. Four task groups have been set up, each dealing with different aspects of social care. Task Group 3 is considering the roles and tasks of social workers. In order to inform the work of this group, the Thomas Coram Research Unit was asked to provide an overview of relevant research and data in three main areas: the effective deployment of social worker time and tasks, improving cross-professional working, and attitudes to take-up of post-qualifying qualifications
Are Wild Bee Pollinator Populations Declining?
How climate change may affect insect pollinator populations in the Midwest.Environmental Change Institute UIUCAgroecology and Sustainable Agriculture Program UIUCunpublishednot peer reviewe
Detecting a rotation in the epsilon Eridani debris disc
The evidence for a rotation of the epsilon Eridani debris disc is examined.
Data at 850 micron wavelength were previously obtained using the Submillimetre
Common User Bolometer Array (SCUBA) over periods in 1997-1998 and 2000-2002. By
chi-square fitting after shift and rotation operations, images from these two
epochs were compared to recover proper motion and orbital motion of the disc.
The same procedures were then performed on simulated images to estimate the
accuracy of the results.
Minima in the chi-square plots indicate a motion of the disc of approximately
0.6'' per year in the direction of the star's proper motion. This
underestimates the true value of 1'' per year, implying that some of the
structure in the disc region is not associated with epsilon Eridani,
originating instead from background galaxies. From the chi-square fitting for
orbital motion, a counterclockwise rotation rate of ~2.75 degrees per year is
deduced. Comparisons with simulated data in which the disc is not rotating show
that noise and background galaxies result in approximately Gaussian
fluctuations with a standard deviation +/-1.5 degrees per year. Thus
counterclockwise rotation of disc features is supported at approximately a
2-sigma level, after a 4-year time difference. This rate is faster than the
Keplerian rate of 0.65 degrees per year for features at ~65 AU from the star,
suggesting their motion is tracking a planet inside the dust ring.
Future observations with SCUBA-2 can rule out no rotation of the epsilon
Eridani dust clumps with ~4-sigma confidence. Assuming a rate of about 2.75
degrees per year, the rotation of the features after a 10-year period could be
shown to be >1 degree per year at the 3-sigma level.Comment: 8 pages, 6 figure
Moving to Extremal Graph Parameters
Which graphs, in the class of all graphs with given numbers n and m of edges
and vertices respectively, minimizes or maximizes the value of some graph
parameter? In this paper we develop a technique which provides answers for
several different parameters: the numbers of edges in the line graph, acyclic
orientations, cliques, and forests. (We minimize the first two and maximize the
third and fourth.)
Our technique involves two moves on the class of graphs. A compression move
converts any graph to a form we call fully compressed: the fully compressed
graphs are split graphs in which the neighbourhoods of points in the
independent set are nested. A second consolidation move takes each fully
compressed graph to one particular graph which we call H(n,m). We show
monotonicity of the parameters listed for these moves in many cases, which
enables us to obtain our results fairly simply.
The paper concludes with some open problems and future directions
Rotation in the Orion Nebula Cluster
Eighteen fields in the Orion Nebula Cluster (ONC) have been monitored for one
or more observing seasons from 1990-99 with a 0.6-m telescope at Wesleyan
University. Photometric data were obtained in Cousins I on 25-40 nights per
season. Results from the first 3 years of monitoring were analyzed by Choi &
Herbst (1996; CH). Here we provide an update based on 6 more years of
observation and the extensive optical and IR study of the ONC by Hillenbrand
(1997) and Hillenbrand et al. (1998). Rotation periods are now available for
134 ONC members. Of these, 67 were detected at multiple epochs with identical
periods by us and 15 more were confirmed by Stassun et al. (1999) in their
study of Ori OBIc/d. The bimodal period distribution for the ONC is confirmed,
but we also find a clear dependence of rotation period on mass. This can be
understood as an effect of deuterium burning, which temporarily slows the
contraction and thus spin-up of stars with M <0.25 solar masses and ages of ~1
My. Stars with M <0.25 solar masses have not had time to bridge the gap in the
period distribution at ~4 days. Excess H-K and I-K emission, as well as CaII
infrared triplet equivalent widths (Hillenbrand et al. 1998), show weak but
significant correlations with rotation period among stars with M >0.25 solar
masses. Our results provide new observational support for the importance of
disks in the early rotational evolution of low mass stars. [abridged]Comment: 18 pages of text, 17 figures, and 4 tables; accepted for publication
in The Astronomical Journa
Doppler-beaming in the Kepler light curve of LHS 6343 A
Context. Kepler observations revealed a brown dwarf eclipsing the M-type star
LHS 6343 A with a period of 12.71 days. In addition, an out-of-eclipse light
modulation with the same period and a relative semi-amplitude of 2 x 10^-4 was
observed showing an almost constant phase lag to the eclipses produced by the
brown dwarf. In a previous work, we concluded that this was due to the light
modulation induced by photospheric active regions in LHS 6343 A. Aims. In the
present work, we prove that most of the out-of-eclipse light modulation is
caused by the Doppler-beaming induced by the orbital motion of the primary
star. Methods. We introduce a model of the Doppler-beaming for an eccentric
orbit and also considered the ellipsoidal effect. The data were fitted using a
Bayesian approach implemented through a Monte Carlo Markov chain method. Model
residuals were analysed by searching for periodicities using a Lomb-Scargle
periodogram. Results. For the first seven quarters of Kepler observations and
the orbit previously derived from the radial velocity measurements, we show
that the light modulation of the system outside eclipses is dominated by the
Doppler-beaming effect. A period search performed on the residuals shows a
significant periodicity of 42.5 +- 3.2 days with a false-alarm probability of 5
x 10^-4, probably associated with the rotational modulation of the primary
component.Comment: 6 pages, 7 figure
Terrestrial Planet Formation I. The Transition from Oligarchic Growth to Chaotic Growth
We use a hybrid, multiannulus, n-body-coagulation code to investigate the
growth of km-sized planetesimals at 0.4-2 AU around a solar-type star. After a
short runaway growth phase, protoplanets with masses of roughly 10^26 g and
larger form throughout the grid. When (i) the mass in these `oligarchs' is
roughly comparable to the mass in planetesimals and (ii) the surface density in
oligarchs exceeds 2-3 g/sq cm at 1 AU, strong dynamical interactions among
oligarchs produce a high merger rate which leads to the formation of several
terrestrial planets. In disks with lower surface density, milder interactions
produce several lower mass planets. In all disks, the planet formation
timescale is roughly 10-100 Myr, similar to estimates derived from the
cratering record and radiometric data.Comment: Astronomical Journal, accepted; 22 pages + 15 figures in ps format;
eps figures at http://cfa-www.harvard.edu/~kenyon/dl/ revised version
clarifies evolution and justifies choice of promotion masse
WASP-1: A lithium- and metal-rich star with an oversized planet
In this paper we present our results of a comprehensive spectroscopicanalysis
of WASP-1, the host star to the exoplanet WASP-1b. We derive T_eff = 6110 +/-
45 K, log g = 4.28 +/- 0.15, and [M/H] = 0.23 +/- 0.08, and also a high
abundance of lithium, log n(Li) = 2.91 +/- 0.05. These parameters suggests an
age for the system of 1-3 Gyr and a stellar mass of 1.25-1.35 M_sun. This means
that WASP-1 has properties very similar to those of HD 149026, the host star
for the highest density planet yet detected. Moreover, their planets orbit at
comparable distances and receive comparable irradiating fluxes from their host
stars. However, despite the similarity of WASP-1 with HD 149026, their planets
have strongly different densities. This suggests that gas-giant planet density
is not a simple function of host-star metallicity or of radiation environment
at ages of ~2 Gyr.Comment: Accepted for publication in MNRAS. 6 pages, 4 figure
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