2,875 research outputs found
Hamilton-Jacobi Theory and Moving Frames
The interplay between the Hamilton-Jacobi theory of orthogonal separation of
variables and the theory of group actions is investigated based on concrete
examples.Comment: This is a contribution to the Vadim Kuznetsov Memorial Issue on
Integrable Systems and Related Topics, published in SIGMA (Symmetry,
Integrability and Geometry: Methods and Applications) at
http://www.emis.de/journals/SIGMA
Twelve-year follow-up of conservative management of postnatal urinary and faecal incontinence and prolapse outcomes : randomised controlled trial
© 2013 Royal College of Obstetricians and Gynaecologists. Funded by Royal College of Obstetricians and Gynaecologists, London, UK; Health Research Council of New Zealand. Grant Number: RG 819/06 New Zealand Lottery Grant Board Health Services Research Unit, University of Aberdeen Chief Scientist Office of the Scottish Government Health DirectoratesPeer reviewedPostprin
Peer-led interventions to prevent tobacco, alcohol and/or drug use among young people aged 11-21 years:a systematic review and meta-analysis
Recommended from our members
Cohort Profile: East London Genes & Health (ELGH), a community based population genomics and health study of British-Bangladeshi and British-Pakistani people
Dust Sensitivity of Absorption-Line Indices
We investigate the effects of dust extinction on integrated absorption-line
indices that are widely used to derive constraints on the ages and
metallicities of composite stellar systems. Typically, absorption-line studies
have been performed on globular clusters or elliptical galaxies, which are
mostly dust-free systems. However, many recent studies of integrated stellar
populations have focused on spiral galaxies which may contain significant
amounts of dust. It is almost universally assumed that the effects of dust
extinction on absorption-line measurements are entirely negligible given the
narrow baseline of the spectral features, but no rigorous study has yet been
performed to verify this conjecture. In this analysis, we explore the
sensitivity of the standard set of Lick absorption-line indices, the
higher-order Balmer line indices, the 4000 A break, the near-IR calcium triplet
indices, and the Rose indices to dust absorption according to population
synthesis models that incorporate a multi-component model for the line and
continuum attenuation due to dust. The latter takes into account the finite
lifetime of stellar birth clouds. While dust does not greatly affect the
line-index measurements for single stellar populations, its effect can be
significant for the 4000 A break or when there is a significant amount of
current star formation.Comment: 19 pages, 15 embedded color figures, uses emulateapj.cls. Submitted
to ApJ. High-resolution version available at
http://www.physics.ubc.ca/~lauren/lickdust_HR.ps.g
Mapping between dissipative and Hamiltonian systems
Theoretical studies of nonequilibrium systems are complicated by the lack of
a general framework. In this work we first show that a transformation
introduced by Ao recently (J. Phys. A {\bf 37}, L25 (2004)) is related to
previous works of Graham (Z. Physik B {\bf 26}, 397 (1977)) and Eyink {\it et
al.} (J. Stat. Phys. {\bf 83}, 385 (1996)), which can also be viewed as the
generalized application of the Helmholtz theorem in vector calculus. We then
show that systems described by ordinary stochastic differential equations with
white noise can be mapped to thermostated Hamiltonian systems. A steady-state
of a dissipative system corresponds to the equilibrium state of the
corresponding Hamiltonian system. These results provides a solid theoretical
ground for corresponding studies on nonequilibrium dynamics, especially on
nonequilibrium steady state. The mapping permits the application of established
techniques and results for Hamiltonian systems to dissipative non-Hamiltonian
systems, those for thermodynamic equilibrium states to nonequilibrium steady
states. We discuss several implications of the present work.Comment: 18 pages, no figure. final version for publication on J. Phys. A:
Math & Theo
The diverse nature of island isolation and its effect on land bridge insular faunas
Aim:
Isolation is a key factor in island biology. It is usually defined as the distance to the geographically nearest mainland, but many other definitions exist. We explored how testing different isolation indices affects the inference of impacts of isolation on faunal characteristics. We focused on land bridge islands and compared the relationships of many spatial and temporal (i.e., through time) isolation indices with community‐, population‐ and individual‐level characteristics (species richness, population density and body size, respectively).
Location:
Aegean Sea islands, Greece.
Time period:
Current.
Taxon:
Many animal taxa.
Methods:
We estimated 21 isolation indices for 205 islands and recorded species richness data for 15 taxa (invertebrates and vertebrates). We obtained body size data for seven lizard species and population density data for three. We explored how well indices predict each characteristic, in each taxon, by conducting a series of ordinary least squares regressions (controlling for island area when needed) and a meta‐analysis.
Results:
Isolation was significantly (and negatively) associated with species richness in 10 of 15 taxa. It was significantly (and positively) associated with body size in only one of seven species and was not associated with population density. The effect of isolation on species richness was much weaker than that of island area, regardless of the index tested. Spatial indices generally out‐performed temporal indices, and indices directly related to the mainland out‐performed those related mainly to neighbouring islands. No index was universally superior to others, including the distance to the geographically nearest mainland.
Main conclusions:
The choice of index can alter our perception of the impacts of isolation on biological patterns. The nearly automatic, ubiquitous use of distance to the geographically nearest mainland misrepresents the complexity of the effects of isolation. We recommend the simultaneous testing of several indices that represent different aspects of isolation, in order to produce more constructive and thorough investigations and avoid imprecise inference
Revising acute care systems and processes to improve breastfeeding and maternal postnatal health: a pre and post intervention study in one English maternity unit
Background
Most women in the UK give birth in a hospital labour ward, following which they are
transferred to a postnatal ward and discharged home within 24 to 48 hours of the birth.
Despite policy and guideline recommendations to support planned, effective postnatal care,
national surveys of women’s views of maternity care have consistently found in-patient
postnatal care, including support for breastfeeding, is poorly rated.
Methods
Using a Continuous Quality Improvement approach, routine antenatal, intrapartum and
postnatal care systems and processes were revised to support implementation of evidence
based postnatal practice. To identify if implementation of a multi-faceted QI intervention
impacted on outcomes, data on breastfeeding initiation and duration, maternal health and
women’s views of care, were collected in a pre and post intervention longitudinal survey.
Primary outcomes included initiation, overall duration and duration of exclusive
breastfeeding. Secondary outcomes included maternal morbidity, experiences and satisfaction
with care. As most outcomes of interest were measured on a nominal scale, these were
compared pre and post intervention using logistic regression.
Results
Data were obtained on 741/1160 (64%) women at 10 days post-birth and 616 (54%) at 3
months post-birth pre-intervention, and 725/1153 (63%) and 575 (50%) respectively postintervention.
Post intervention there were statistically significant differences in the initiation
(p = 0.050), duration of any breastfeeding (p = 0.020) and duration of exclusive breastfeeding
to 10 days (p = 0.038) and duration of any breastfeeding to three months (p = 0.016). Post
intervention, women were less likely to report physical morbidity within the first 10 days of
birth, and were more positive about their in-patient care.
Conclusions
It is possible to improve outcomes of routine in-patient care within current resources through
continuous quality improvement
Structure of Disk Dominated Galaxies I. Bulge/Disk Parameters, Simulations, and Secular Evolution
(Abridged) A robust analysis of galaxy structural parameters, based on the
modeling of bulge and disk brightnesses in the BVRH bandpasses, is presented
for 121 face-on and moderately inclined late-type spirals. Each surface
brightness (SB) profile is decomposed into a sum of a generalized Sersic bulge
and an exponential disk. The reliability and limitations of our bulge-to-disk
(B/D) decompositions are tested with extensive simulations of galaxy brightness
profiles (1D) and images (2D). Galaxy types are divided into 3 classes
according to their SB profile shapes; Freeman Type-I and Type-II, and a third
``Transition'' class for galaxies whose profiles change from Type-II in the
optical to Type-I in the infrared. We discuss possible interpretations of
Freeman Type-II profiles. The Sersic bulge shape parameter for nearby Type-I
late-type spirals shows a range between n=0.1-2 but, on average, the underlying
surface density profile for the bulge and disk of these galaxies is adequately
described by a double-exponential distribution. We confirm a coupling between
the bulge and disk with a scale length ratio r_e/h=0.22+/-0.09, or
h_bulge/h_disk=0.13+/-0.06 for late-type spirals, in agreement with recent
N-body simulations of disk formation and models of secular evolution. This
ratio increases from ~0.20 for late-type spirals to ~0.24 for earlier types.
The similar scaling relations for early and late-type spirals suggest
comparable formation and/or evolution scenarios for disk galaxies of all Hubble
types.Comment: 78 pages with 23 embedded color figures + tables of galaxy structural
parameters. Accepted for publication in the Astrophysical Journal. The
interested reader is strongly encouraged to ignore some of the low res
figures within; instead, download the high resolution version from
http://www.astro.ubc.ca/people/courteau/public/macarthur02_disks.ps.g
Using historical woodland creation to construct a long-term, large-scale natural experiment: The WrEN project
Natural experiments have been proposed as a way of complementing manipulative experiments to improve ecological understanding and guide management. There is a pressing need for evidence from such studies to inform a shift to landscape-scale conservation, including the design of ecological networks. Although this shift has been widely embraced by conservation communities worldwide, the empirical evidence is limited and equivocal, and may be limiting effective conservation. We present principles for well-designed natural experiments to inform landscape-scale conservation and outline how they are being applied in the WrEN project, which is studying the effects of 160years of woodland creation on biodiversity in UK landscapes. We describe the study areas and outline the systematic process used to select suitable historical woodland creation sites based on key site- and landscape-scale variables – including size, age, and proximity to other woodland. We present the results of an analysis to explore variation in these variables across sites to test their suitability as a basis for a natural experiment. Our results confirm that this landscape satisfies the principles we have identified and provides an ideal study system for a long-term, large-scale natural experiment to explore how woodland biodiversity is affected by different site and landscape attributes. The WrEN sites are now being surveyed for a wide selection of species that are likely to respond differently to site- and landscape-scale attributes and at different spatial and temporal scales. The results from WrEN will help develop detailed recommendations to guide landscape-scale conservation, including the design of ecological networks. We also believe that the approach presented demonstrates the wider utility of well-designed natural experiments to improve our understanding of ecological systems and inform policy and practice
- …