1,168 research outputs found
Dissolving star cluster candidates
We present a list of 34 neglected entries from star cluster catalogues
located at relatively high galactic latitudes ( 15) which
appear to be candidate late stages of star cluster dynamical evolution.
Although underpopulated with respect to usual open clusters, they still present
a high number density contrast as compared to the galactic field. This was
verified by means of (i) predicted model counts from different galactic
subsystems in the same direction, and (ii) Guide Star Catalog equal solid angle
counts for the object and surrounding fields. This suggests that the objects
are physical systems, possibly star clusters in the process of disruption or
their fossil remains. The sample will be useful for followup studies in view of
verifying their physi cal nature.Comment: manuscript in LATEX with 7 pages, 7 figures .ps Accepted for
Astronomy and Astrophysics main journa
Dynamical Evolution of Young Embedded Clusters: A Parameter Space Survey
This paper investigates the dynamical evolution of embedded stellar clusters
from the protocluster stage, through the embedded star-forming phase, and out
to ages of 10 Myr -- after the gas has been removed from the cluster. The
relevant dynamical properties of young stellar clusters are explored over a
wide range of possible star formation environments using N-body simulations.
Many realizations of equivalent initial conditions are used to produce robust
statistical descriptions of cluster evolution including the cluster bound
fraction, radial probability distributions, as well as the distributions of
close encounter distances and velocities. These cluster properties are
presented as a function of parameters describing the initial configuration of
the cluster, including the initial cluster membership N, initial stellar
velocities, cluster radii, star formation efficiency, embedding gas dispersal
time, and the degree of primordial mass segregation. The results of this
parameter space survey, which includes about 25,000 simulations, provide a
statistical description of cluster evolution as a function of the initial
conditions. We also present a compilation of the FUV radiation fields provided
by these same cluster environments. The output distributions from this study
can be combined with other calculations, such as disk photoevaporation models
and planetary scattering cross sections, to ascertain the effects of the
cluster environment on the processes involved in planet formation.Comment: 65 pages including 20 figures, accepted to ApJ Supplemen
Canonical Melnikov theory for diffeomorphisms
We study perturbations of diffeomorphisms that have a saddle connection
between a pair of normally hyperbolic invariant manifolds. We develop a
first-order deformation calculus for invariant manifolds and show that a
generalized Melnikov function or Melnikov displacement can be written in a
canonical way. This function is defined to be a section of the normal bundle of
the saddle connection.
We show how our definition reproduces the classical methods of Poincar\'{e}
and Melnikov and specializes to methods previously used for exact symplectic
and volume-preserving maps. We use the method to detect the transverse
intersection of stable and unstable manifolds and relate this intersection to
the set of zeros of the Melnikov displacement.Comment: laTeX, 31 pages, 3 figure
The velocity distribution of nearby stars from Hipparcos data II. The nature of the low-velocity moving groups
The velocity distribution of nearby stars contains many "moving groups" that
are inconsistent with the standard assumption of an axisymmetric,
time-independent, and steady-state Galaxy. We study the age and metallicity
properties of the low-velocity moving groups based on the reconstruction of the
local velocity distribution in Paper I of this series. We perform stringent,
conservative hypothesis testing to establish for each of these moving groups
whether it could conceivably consist of a coeval population of stars. We
conclude that they do not: the moving groups are not trivially associated with
their eponymous open clusters nor with any other inhomogeneous star formation
event. Concerning a possible dynamical origin of the moving groups, we test
whether any of the moving groups has a higher or lower metallicity than the
background population of thin disk stars, as would generically be the case if
the moving groups are associated with resonances of the bar or spiral
structure. We find clear evidence that the Hyades moving group has higher than
average metallicity and weak evidence that the Sirius moving group has lower
than average metallicity, which could indicate that these two groups are
related to the inner Lindblad resonance of the spiral structure. Further we
find weak evidence that the Hercules moving group has higher than average
metallicity, as would be the case if it is associated with the bar's outer
Lindblad resonance. The Pleiades moving group shows no clear metallicity
anomaly, arguing against a common dynamical origin for the Hyades and Pleiades
groups. Overall, however, the moving groups are barely distinguishable from the
background population of stars, raising the likelihood that the moving groups
are associated with transient perturbations. [abridged
Optical properties of the iron-chalcogenide superconductor FeTe0.55Se0.45
The complex optical properties of the iron-chalcogenide superconductor
FeTe0.55Se0.45 with Tc=14K have been examined over a wide frequency range for
light polarized in the Fe-Te(Se) planes above and below Tc. At room temperature
the optical response may be described by a weakly-interacting Fermi liquid;
however, just above Tc this picture breaks down and the scattering rate takes
on a linear frequency dependence. Below Tc there is evidence for two gap
features in the optical conductivity at Delta_1 ~ 2.5 meV and Delta_2 ~ 5.1
meV. Less than 20% of the free carriers collapse into the condensate for T <<
Tc, and this material is observed to fall on the universal scaling line for a
BCS dirty-limit superconductor in the weak-coupling limit.Comment: 6 pages, 6 figures; accepted J. Phys. Chem. Solids, proceedings of
SNS2010 in Shanghai (updated references
Nutrient-extraction blender preparation reduces postprandial glucose responses from fruit juice consumption
The prognostic value of systemic inflammation in patients undergoing surgery for colon cancer: comparison of composite ratios and cumulative scores
Introduction:
The systemic inflammatory response has been proven to have a prognostic value. There are two methods of assessing the systemic inflammatory response composite ratios (R) and cumulative scores (S). The aim of this study was to compare the prognostic value of ratios and scores in patients undergoing surgery for colon cancer.
Methods:
Patients were identified prospectively in a single surgical unit. Preoperative neutrophil (N), lymphocyte (L), monocyte (M) and platelet (P) counts, CRP (C) and albumin (A) levels were recorded. The relationship between composite ratios neutrophilâlymphocyte ratio (NLR), plateletâlymphocyte ratio (PLR), lymphocyteâmonocyte ratio (LMR), C-reactive protein albumin ratio (CAR) and the cumulative scores neutrophilâ lymphocyte score (NLS), plateletâlymphocyte score (PLS), lymphocyteâmonocyte score (LMS), neutrophilâ platelet score (NPS), modified Glasgow prognostic score (mGPS) and clinicopathological characteristics, cancer-specific survival (CSS) and overall survival (OS), were examined.
Results:
A total of 801 patients were examined. When adjusted for tumour node metastasis (TNM) stage, NLR >5 (pâ<â0.001), NLS (pâ<â0.01), PLS (pâ<â0.001), LMR <2.4 (pâ<â0.001), LMS (pâ<â0.001), NPS (pâ<â0.001), CAR >0.22 (pâ<â0.001) and mGPS (pâ<â0.001) were significantly associated with CSS. In patients undergoing elective surgery (nâ=â689), the majority of the composite ratios/scores correlated with age (pâ<â0.01), BMI (pâ<â0.01), T stage (pâ<â0.01), venous invasion (pâ<â0.01) and peritoneal involvement (pâ<â0.01). When NPS (myeloid) and mGPS (liver) were directly compared, their relationship with CSS and OS was similar.
Conclusions:
Both composite ratios and cumulative scores had prognostic value, independent of TNM stage, in patients with colon cancer. However, cumulative scores, based on normal reference ranges, are simpler and more consistent for clinical use
The Roles of the S3MPC: Monitoring, Validation and Evolution of Sentinel-3 Altimetry Observations
The Sentinel-3 Mission Performance Centre (S3MPC) is tasked by the European Space Agency (ESA) to monitor the health of the Copernicus Sentinel-3 satellites and ensure a high data quality to the users. This paper deals exclusively with the effort devoted to the altimeter and microwave radiometer, both components of the Surface Topography Mission (STM). The altimeters on Sentinel-3A and -3B are the first to operate in delay-Doppler or SAR mode over all Earth surfaces, which enables better spatial resolution of the signal in the along-track direction and improved noise reduction through multi-looking, whilst the radiometer is a two-channel nadir-viewing system. There are regular routine assessments of the instruments through investigation of telemetered housekeeping data, calibrations over selected sites and comparisons of geophysical retrievals with models, in situ data and other satellite systems. These are performed both to monitor the daily production, assessing the uncertainties and errors on the estimates, and also to characterize the long-term performance for climate science applications. This is critical because an undetected drift in performance could be misconstrued as a climate variation. As the data are used by the Copernicus Services (e.g., CMEMS, Global Land Monitoring Services) and by the research community over open ocean, coastal waters, sea ice, land ice, rivers and lakes, the validation activities encompass all these domains, with regular reports openly available. The S3MPC is also in charge of preparing improvements to the processing, and of the development and tuning of algorithms to improve their accuracy. This paper is thus the first refereed publication to bring together the analysis of SAR altimetry across all these different domains to highlight the benefits and existing challenges
Adjuvant radiotherapy and chemotherapy in breast cancer: 30 year follow-up of survival
BACKGROUND:The long term outcome (more than 15 years) of adjuvant treatment in patients with primary operable breast cancer has rarely been examined.METHODS:A randomised clinical trial of radiotherapy, chemotherapy (28 day cycles of cyclophosphamide, methotrexate and 5-fluorouracil) or both on women with primary operable breast cancer (n = 322) was followed-up for a median of 27 years.RESULTS:260 (81%) patients died, 204 (78%) from breast cancer. Cancer specific survival (SE) at 10 years, 20 years and 30 years was 41 (3)%, 34 (3)% and 33 (3)% respectively. Presence of more than 3 involved lymph nodes increased cancer-specific mortality (HR 1.88, 95% CI 1.34-2.63) after adjustment for age, socio-economic deprivation and adjuvant treatment. Both age (HR 1.63, 95% CI 1.19-2.22) and involved lymph nodes (HR 1.59, 95% CI 1.17-2.14) were significant predictors of all-cause mortality after adjustment for other factors. There was no significant difference in all-cause or cancer-specific survival between patients in each of the 3 treatment arms.CONCLUSIONS:The present study highlights the long term impact of node positive disease but does not indicate that any regimen was associated with significantly better long-term surviva
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