2,895 research outputs found
A difference boosting neural network for automated star-galaxy classification
In this paper we describe the use of a new artificial neural network, called
the difference boosting neural network (DBNN), for automated classification
problems in astronomical data analysis. We illustrate the capabilities of the
network by applying it to star galaxy classification using recently released,
deep imaging data. We have compared our results with classification made by the
widely used Source Extractor (SExtractor) package. We show that while the
performance of the DBNN in star-galaxy classification is comparable to that of
SExtractor, it has the advantage of significantly higher speed and flexibility
during training as well as classification.Comment: 9 pages, 1figure, 7 tables, accepted for publication in Astronomy and
Astrophysic
Connections Between Local and Global Turbulence in Accretion Disks
We analyze a suite of global magnetohydrodynamic (MHD) accretion disk
simulations in order to determine whether scaling laws for turbulence driven by
the magnetorotational instability, discovered via local shearing box studies,
are globally robust. The simulations model geometrically-thin disks with zero
net magnetic flux and no explicit resistivity or viscosity. We show that the
local Maxwell stress is correlated with the self-generated local vertical
magnetic field in a manner that is similar to that found in local simulations.
Moreover, local patches of vertical field are strong enough to stimulate and
control the strength of angular momentum transport across much of the disk. We
demonstrate the importance of magnetic linkages (through the low-density
corona) between different regions of the disk in determining the local field,
and suggest a new convergence requirement for global simulations -- the
vertical extent of the corona must be fully captured and resolved. Finally, we
examine the temporal convergence of the average stress, and show that an
initial long-term secular drift in the local flux-stress relation dies away on
a time scale that is consistent with turbulent mixing of the initial magnetic
field.Comment: 8 Pages, 7 Figures ApJ, In Pres
On the interaction of Jupiter's Great Red Spot and zonal jet streams
In this paper, Jupiter's Great Red Spot (GRS) is used to determine properties
of the Jovian atmosphere that cannot otherwise be found. These properties
include the potential vorticity of the GRS and its neighboring jet streams, the
shear imposed on the GRS by the jet streams, and the vertical entropy gradient
(i.e., Rossby deformation radius). The cloud cover of the GRS, which is often
used to define the GRS's area and aspect ratio, is found to differ
significantly from the region of the GRS's potential vorticity anomaly. The
westward-going jet stream to the north of the GRS and the eastward-going jet
stream to its south are each found to have a large potential vorticity
``jump''. The jumps have opposite sign and as a consequence of their
interaction with the GRS, the shear imposed on the GRS is reduced. The
east-west to north-south aspect ratio of the GRS's potential vorticity anomaly
depends on the ratio of the imposed shear to the strength of the anomaly. The
aspect ratio is found to be 2:1, but without the opposing jumps it
would be much greater. The GRS's high-speed collar and quiescent interior
require that the potential vorticity in the interior be approximately half that
in the collar. No other persistent geophysical vortex has a significant minimum
of potential vorticity in its interior and laboratory vortices with such a
minimum are unstable.Comment: Manuscript accepted to Journal of the Atmospheric Sciences, March
2007. v2: minor stylistic changes (after journal proof reading
Fold Designability, Distribution, and Disease
Fold designability has been estimated by the number of families contained in that fold. Here, we show that among orthologous proteins, sequence divergence is higher for folds with greater numbers of families. Folds with greater numbers of families also tend to have families that appear more often in the proteome and greater promiscuity (the number of unique âpartnerâ folds that the fold is found with within the same protein). We also find that many disease-related proteins have folds with relatively few families. In particular, a number of these proteins are associated with diseases occurring at high frequency. These results suggest that family counts reflect how certain structures are distributed in nature and is an important characteristic associated with many human diseases
Treatment Patterns and Health Resource Utilization Among Patients Diagnosed With Early Stage Resected NonâSmall Cell Lung Cancer at US Community Oncology Practices
AbstractBackgroundPlatin-based adjuvant chemotherapy has extended survival in clinical trials in patients with completely resected nonâsmall cell lung cancer (NSCLC). There are few data on the use of adjuvant therapy in community-based clinical practice in the United States.Materials and MethodsThis was a retrospective observational study using electronic medical record and billing data collected during routine care at US community oncology sites in the Vector Oncology Data Warehouse between January 2007 and January 2014. Patients aged ℠18 years with a primary diagnosis of stage IB to IIIA NSCLC were eligible if they had undergone surgical resection. Treatment patterns, health care resource use, and cost were recorded, stratified by stage at diagnosis.ResultsThe study included 609 patients (mean age, 64.8 years, 52.9% male), of whom 215 had stage IB disease, 130 stage IIA/II, 110 stage IIB, and 154 stage IIIA. Adjuvant systemic therapy after resection was provided to 345 (56.7%) of 609 patients, with lower use in patients with stage IB disease (39.1%) than stage II to IIIA disease (64.9-68.2%) (P < .0001). The most common adjuvant regimen at all stages was the combination of carboplatin and paclitaxel. There were no statistically significant differences in office visits or incidence of hospitalization by disease stage. During adjuvant treatment, the total monthly median cost per patient was 8,815.61 to $23,360.85).ConclusionAdjuvant systemic therapy was used in some patients with stage IB NSCLC and in the majority of patients with stage IIA to IIIA disease. There were few differences in regimen or health care resource use by disease stage
Resonant Transfer and Excitation in Li-Like F Colliding with Hâ
We have measured coincidences between x rays and projectiles that have captured one electron in F6+ + H2 collisions at projectile energies between 15 and 33 MeV. The cross sections for capture and simultaneous x-ray emission as a function of projectile energy show clear structures. Indications of an unexpectedly high population of high-n states predominantly formed by resonant transfer and excitation (RTE) were found. Above the Kln (n\u3e1) RTE resonance energies another maximum was observed
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