4,956 research outputs found
On the Optimization of Mixture Resolving Signal Processing Structures
Mixture resolving signal processing optimization with optimum linear detection operators and mixture resolving estimator
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
Natural ocean carbon cycle sensitivity to parameterizations of the recycling in a climate model
Sensitivities of the oceanic biological pump within the GISS (Goddard Institute for Space Studies ) climate modeling
system are explored here. Results are presented from twin control simulations
of the air–sea CO<sub>2</sub> gas exchange using two different ocean models coupled
to the same atmosphere. The two ocean models (Russell ocean model and Hybrid
Coordinate Ocean Model, HYCOM) use different vertical coordinate systems, and
therefore different representations of column physics. Both variants of the
GISS climate model are coupled to the same ocean biogeochemistry module (the
NASA Ocean Biogeochemistry Model, NOBM), which computes prognostic
distributions for biotic and abiotic fields that influence the air–sea flux
of CO<sub>2</sub> and the deep ocean carbon transport and storage. In particular, the
model differences due to remineralization rate changes are compared to
differences attributed to physical processes modeled differently in the two
ocean models such as ventilation, mixing, eddy stirring and vertical
advection. GISSEH(GISSER) is found to underestimate mixed layer depth
compared to observations by about 55% (10%) in the Southern Ocean
and overestimate it by about 17% (underestimate by 2%) in the
northern high latitudes. Everywhere else in the global ocean, the two models
underestimate the surface mixing by about 12–34%, which prevents deep
nutrients from reaching the surface and promoting primary production there.
Consequently, carbon export is reduced because of reduced production at the
surface. Furthermore, carbon export is particularly sensitive to
remineralization rate changes in the frontal regions of the subtropical gyres
and at the Equator and this sensitivity in the model is much higher than the
sensitivity to physical processes such as vertical mixing, vertical advection
and mesoscale eddy transport. At depth, GISSER, which has a significant warm
bias, remineralizes nutrients and carbon faster thereby producing more nutrients and
carbon at depth, which eventually resurfaces with the global thermohaline
circulation especially in the Southern Ocean. Because of the reduced primary
production and carbon export in GISSEH compared to GISSER, the biological
pump efficiency, i.e., the ratio of primary production and carbon export at
75 m, is half in the GISSEH of that in GISSER, The Southern Ocean emerges as
a key region where the CO<sub>2</sub> flux is as sensitive to biological
parameterizations as it is to physical parameterizations. The fidelity of
ocean mixing in the Southern Ocean compared to observations is shown to be a
good indicator of the magnitude of the biological pump efficiency regardless
of physical model choice
Pharmacological Facilitation of Coronary Intervention in ST-Segment Elevation Myocardial Infarction Time Is of the Essence⁎⁎Editorials published in JACC: Cardiovascular Interventions reflect the views of the authors and do not necessarily represent the views of JACC: Cardiovascular Interventions or the American College of Cardiology.
Spatial Variability in Column CO2 Inferred from High Resolution GEOS-5 Global Model Simulations: Implications for Remote Sensing and Inversions
Column CO2 observations from current and future remote sensing missions represent a major advancement in our understanding of the carbon cycle and are expected to help constrain source and sink distributions. However, data assimilation and inversion methods are challenged by the difference in scale of models and observations. OCO-2 footprints represent an area of several square kilometers while NASA s future ASCENDS lidar mission is likely to have an even smaller footprint. In contrast, the resolution of models used in global inversions are typically hundreds of kilometers wide and often cover areas that include combinations of land, ocean and coastal areas and areas of significant topographic, land cover, and population density variations. To improve understanding of scales of atmospheric CO2 variability and representativeness of satellite observations, we will present results from a global, 10-km simulation of meteorology and atmospheric CO2 distributions performed using NASA s GEOS-5 general circulation model. This resolution, typical of mesoscale atmospheric models, represents an order of magnitude increase in resolution over typical global simulations of atmospheric composition allowing new insight into small scale CO2 variations across a wide range of surface flux and meteorological conditions. The simulation includes high resolution flux datasets provided by NASA s Carbon Monitoring System Flux Pilot Project at half degree resolution that have been down-scaled to 10-km using remote sensing datasets. Probability distribution functions are calculated over larger areas more typical of global models (100-400 km) to characterize subgrid-scale variability in these models. Particular emphasis is placed on coastal regions and regions containing megacities and fires to evaluate the ability of coarse resolution models to represent these small scale features. Additionally, model output are sampled using averaging kernels characteristic of OCO-2 and ASCENDS measurement concepts to create realistic pseudo-datasets. Pseudo-data are averaged over coarse model grid cell areas to better understand the ability of measurements to characterize CO2 distributions and spatial gradients on both short (daily to weekly) and long (monthly to seasonal) time scale
Challenging Issues in Clinical Trial Design: Part 4 of a 4-Part Series on Statistics for Clinical Trials.
As a sequel to last week's paper on the fundamentals of clinical trial design, this paper tackles related controversial issues: noninferiority trials, the value of factorial designs, the importance and challenges of strategy trials, Data Monitoring Committees (including when to stop a trial early), and the role of adaptive designs. All topics are illustrated by relevant examples from cardiology trials
Design of Major Randomized Trials: Part 3 of a 4-Part Series on Statistics for Clinical Trials.
This paper provides practical guidance on the fundamentals of design for major randomized controlled trials. Topics covered include the choice of patients, choice of treatment and control groups, choice of primary and secondary endpoints, methods of randomization, appropriate use of blinding, and determination of trial size. Insights are made with reference to contemporary major trials in cardiology
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