2,012 research outputs found
Applications of Machine-Learning Algorithms for Infrared Colour Selection of Galactic Wolf-Rayet Stars
We have investigated and applied machine-learning algorithms for Infrared
Colour Selection of Galactic Wolf-Rayet (WR) candidates. Objects taken from the
GLIMPSE catalogue of the infrared objects in the Galactic plane can be
classified into different stellar populations based on the colours inferred
from their broadband photometric magnitudes (, and from 2MASS, and
the four \textit{Spitzer}/IRAC bands). The algorithms tested in this pilot
study are variants of the -Nearest Neighbours (-NN) approach, which is
ideal for exploratory studies of classification problems where interrelations
between variables and classes are complicated. The aims of this study are (1)
to provide an automated tool to select reliable WR candidates and potentially
other classes of objects, (2) to measure the efficiency of infrared colour
selection at performing these tasks and, (3) to lay the groundwork for
statistically inferring the total number of WR stars in our Galaxy. We report
the performance results obtained over a set of known objects and selected
candidates for which we have carried out follow-up spectroscopic observations,
and confirm the discovery of 4 new WR stars.Comment: Authors' version of published paper, now at MNRAS, 473, 256
Staggered Flux Phase in a Model of Strongly Correlated Electrons
We present numerical evidence for the existence of a staggered flux (SF)
phase in the half-filled two-leg t-U-V-J ladder, with true long-range order in
the counter-circulating currents. The density-matrix renormalization-group
(DMRG) / finite-size scaling approach, generalized to describe complex-valued
Hamiltonians and wavefunctions, is employed. The SF phase exhibits robust
currents at intermediate values of the interaction strength.Comment: Version to appear in Phys. Rev. Let
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Comparing proxy rated quality of life of people living with dementia in care homes
Background: Improving quality of life (QOL) for people with dementia is a priority. In care homes, we often rely on proxy ratings from staff and family but we do not know if, or how, they differ in care homes.
Methods: We compared 1056 pairs of staff and family DEMQOL-Proxy ratings from 86 care homes across England. We explored factors associated with ratings quantitatively using multilevel modelling and, qualitatively, through thematic analysis of 12 staff and 12 relative interviews.
Results: Staff and family ratings were weakly correlated (ρs = 0.35). Median staff scores were higher than family's (104 v. 101; p < 0.001). Family were more likely than staff to rate resident QOL as ‘Poor’ (χ2 = 55.91, p < 0.001). Staff and family rated QOL higher when residents had fewer neuropsychiatric symptoms and severe dementia. Staff rated QOL higher in homes with lower staff:resident ratios and when staff were native English speakers. Family rated QOL higher when the resident had spent longer living in the care home and was a native English. Spouses rated residents’ QOL higher than other relatives. Qualitative results suggest differences arise because staff felt good care provided high QOL but families compared the present to the past. Family judgements centre on loss and are complicated by decisions about care home placement and their understandings of dementia.
Conclusion: Proxy reports differ systematically between staff and family. Reports are influenced by the rater:staff and family may conceptualise QOL differently
Polarisation Observations of HO 620.701 GHz Maser Emission with Herschel/HIFI in Orion KL
Context. The high intensities and narrow bandwidths exhibited by some
astronomical masers make them ideal tools for studying star-forming giant
molecular clouds. The water maser transition at
620.701 GHz can only be observed from above Earth's strongly absorbing
atmosphere; its emission has recently been detected from space. Aims. We sought
to further characterize the star-forming environment of Orion KL by
investigating the linear polarisation of a source emitting a narrow 620.701 GHz
maser feature with the heterodyne spectrometer HIFI on board the Herschel Space
Observatory. Methods. High-resolution spectral datasets were collected over a
thirteen month period beginning in 2011 March, to establish not only the linear
polarisation but also the temporal variability of the source. Results. Within a
uncertainty, no polarisation was detected to an upper limit of
approximately 2%. These results are compared with coeval linear polarisation
measurements of the 22.235 GHz maser line from
the Effelsberg 100-m radio telescope, typically a much stronger maser
transition. Although strongly polarised emission is observed for one component
of the 22.235 GHz maser at 7.2 km s, a weaker component at the same
velocity as the 620.701 GHz maser at 11.7 km s is much less polarised.Comment: Accepted for publication in A&
SU(N) quantum spin models: A variational wavefunction study
The study of SU(N) quantum spin models is relevant to a variety of physical
systems including ultracold atoms in optical lattices, and also leads to
insights into novel quantum phases and phase transitions of SU(2) spin models.
We use Gutzwiller projected fermionic variational wavefunctions to explore the
phase diagram and correlation functions of SU(N) spin models in the
self-conjugate representation, with Heisenberg bilinear and biquadratic
interactions. In 1D, the variational phase diagram of the SU(4) spin chain is
constructed by examining instabilities of the Gutzwiller projected free fermion
ground state to various broken symmetries, and it agrees well with exact
results.The spin and dimer correlations of the Gutzwiller projected free
fermion state with N flavors of fermions are also in good agreement with exact
and 1/N calculations for the critical points of SU(N) spin chains. In 2D, the
variational phase diagram on the square lattice is obtained by studying
instabilities of the Gutzwiller projected pi-flux state. The variational ground
state of the pure Heisenberg model is found to exhibit long range Neel order
for N=2,4 and spin Peierls order for N > 4. For N=4 and 6, biquadratic
interactions lead to a complex phase diagram which includes an extended valence
bond crystal in both cases, as well as a stable pi-flux phase for N=6. The spin
correlations of the projected pi-flux state at N=4 are in good agreement with
1/N calculations. We find that this state also shows strongly enhanced dimer
correlations, in qualitative accord with the large-N results. We compare our
results with a recent QMC study of the SU(4) Heisenberg model.Comment: 22 pages, 7 figs, added references to arxiv versio
Environmental hydro-refugia demonstrated by vegetation vigour in the Okavango Delta, Botswana
Climate shifts at decadal scales can have environmental consequences, and therefore, identifying areas that act as environmental refugia is valuable in understanding future climate variability. Here we illustrate how, given appropriate geohydrology, a rift basin and its catchment can buffer vegetation response to climate signals on decadal time-scales, therefore exerting strong local environmental control. We use time-series data derived from Normalised Difference Vegetation Index (NDVI) residuals that record vegetation vigour, extracted from a decadal span of MODIS images, to demonstrate hydrogeological buffering. While this has been described previously it has never been demonstrated via remote sensing and results in relative stability in vegetation vigour inside the delta, compared to that outside. As such the Delta acts as a regional hydro-refugium. This provides insight, not only to the potential impact of future climate in the region, but also demonstrates why similar basins are attractive to fauna, including our ancestors, in regions like eastern Africa. Although vertebrate evolution operates on time scales longer than decades, the sensitivity of rift wetlands to climate change has been stressed by some authors, and this work demonstrates another example of the unique properties that such basins can afford, given the right hydrological conditions
Sources of Stress, Family Functioning, and Needs of Families With a Chronic Critically Ill Child: A Qualitative Study.
PICU hospitalization is particularly stressful for families. When it is prolonged and the prognostic is uncertain, it can significantly and negatively affect the whole family. To date, little is known on how families with a chronic critically ill (CCI) child are affected. This national study explored the specific PICU-related sources of stress, family functioning and needs of families of CCI patients during a PICU hospitalization. This descriptive qualitative study was conducted in the eight pediatric intensive care units in Switzerland. Thirty-one families with a child meeting the CCI criteria participated in semi-structured interviews. Interviews, including mothers only (n = 12), fathers only (n = 8), or mother and father dyads (n = 11), were conducted in German, French, or English by two trained researchers/clinical nurses specialists. Interviews were recorded, transcribed verbatim, and analyzed using deductive and inductive content analyses. Five overarching themes emerged: (1) high emotional intensity, (2) PICU-related sources of stress, (3) evolving family needs, (4) multi-faceted family functioning, and (5) implemented coping strategies. Our study highlighted the importance of caring for families with CCI children. Parents reported high negative emotional responses that affect their family functioning. Families experience was highly dependent on how HCPs were able to meet the parental needs, provide emotional support, reinforce parental empowerment, and allow high quality of care coordination
Applicability of different onboard routing and processing techniques to mobile satellite systems
The paper summarizes a study contract recently undertaken for ESA. The study compared the effectiveness of several processing architectures applied to multiple beam, geostationary global and European regional missions. The paper discusses architectures based on transparent SS-FDMA analog, transparent DSP and regenerative processing. Quantitative comparisons are presented and general conclusions are given with respect to suitability of the architectures to different mission requirements
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