30,179 research outputs found
Optimal combining of ground-based sensors for the purpose of validating satellite-based rainfall estimates
Two problems related to radar rainfall estimation are described. The first part is a description of a preliminary data analysis for the purpose of statistical estimation of rainfall from multiple (radar and raingage) sensors. Raingage, radar, and joint radar-raingage estimation is described, and some results are given. Statistical parameters of rainfall spatial dependence are calculated and discussed in the context of optimal estimation. Quality control of radar data is also described. The second part describes radar scattering by ellipsoidal raindrops. An analytical solution is derived for the Rayleigh scattering regime. Single and volume scattering are presented. Comparison calculations with the known results for spheres and oblate spheroids are shown
Gaia eclipsing binary and multiple systems. Two-Gaussian models applied to OGLE-III eclipsing binary light curves in the Large Magellanic Cloud
The advent of large scale multi-epoch surveys raises the need for automated
light curve (LC) processing. This is particularly true for eclipsing binaries
(EBs), which form one of the most populated types of variable objects. The Gaia
mission, launched at the end of 2013, is expected to detect of the order of few
million EBs over a 5-year mission.
We present an automated procedure to characterize EBs based on the geometric
morphology of their LCs with two aims: first to study an ensemble of EBs on a
statistical ground without the need to model the binary system, and second to
enable the automated identification of EBs that display atypical LCs. We model
the folded LC geometry of EBs using up to two Gaussian functions for the
eclipses and a cosine function for any ellipsoidal-like variability that may be
present between the eclipses. The procedure is applied to the OGLE-III data set
of EBs in the Large Magellanic Cloud (LMC) as a proof of concept. The bayesian
information criterion is used to select the best model among models containing
various combinations of those components, as well as to estimate the
significance of the components.
Based on the two-Gaussian models, EBs with atypical LC geometries are
successfully identified in two diagrams, using the Abbe values of the original
and residual folded LCs, and the reduced . Cleaning the data set from
the atypical cases and further filtering out LCs that contain non-significant
eclipse candidates, the ensemble of EBs can be studied on a statistical ground
using the two-Gaussian model parameters. For illustration purposes, we present
the distribution of projected eccentricities as a function of orbital period
for the OGLE-III set of EBs in the LMC, as well as the distribution of their
primary versus secondary eclipse widths.Comment: 20 pages, 29 figures. Submitted to A&
Rotational behavior of red blood cells in suspension---a mesoscale simulation study
The nature of blood as a suspension of red blood cells makes computational
hemodynamics a demanding task. Our coarse-grained blood model, which builds on
a lattice Boltzmann method for soft particle suspensions, enables the study of
the collective behavior of the order of 10^6 cells in suspension. After
demonstrating the viscosity measurement in Kolmogorov flow, we focus on the
statistical analysis of the cell orientation and rotation in Couette flow. We
quantify the average inclination with respect to the flow and the nematic order
as a function of shear rate and hematocrit. We further record the distribution
of rotation periods around the vorticity direction and find a pronounced peak
in the vicinity of the theoretical value for free model cells even though
cell-cell interactions manifest themselves in a substantial width of the
distribution.Comment: 8 pages, 5 figure
The formation of CDM haloes I: Collapse thresholds and the ellipsoidal collapse model
In the excursion set approach to structure formation initially spherical
regions of the linear density field collapse to form haloes of mass at
redshift if their linearly extrapolated density contrast, averaged
on that scale, exceeds some critical threshold, .
The value of is often calculated from the
spherical or ellipsoidal collapse model, which provide well-defined predictions
given auxiliary properties of the tidal field at a given location. We use two
cosmological simulations of structure growth in a cold dark matter
scenario to quantify , its dependence on the
surrounding tidal field, as well as on the shapes of the Lagrangian regions
that collapse to form haloes at . Our results indicate that the
ellipsoidal collapse model provides an accurate description of the mean
dependence of on both the strength of the tidal
field and on halo mass. However, for a given , depends strongly on the halo's characteristic formation
redshift: the earlier a halo forms, the higher its initial density contrast.
Surprisingly, the majority of haloes forming fall below the ellipsoidal
collapse barrier, contradicting the model predictions. We trace the origin of
this effect to the non-spherical shapes of Lagrangian haloes, which arise
naturally due to the asymmetry of the linear tidal field. We show that a
modified collapse model, that accounts for the triaxial shape of protohaloes,
provides a more accurate description of the measured minimum overdensities of
recently collapsed objects.Comment: MNRAS in pres
Gaia Eclipsing Binary and Multiple Systems. A study of detectability and classification of eclipsing binaries with Gaia
In the new era of large-scale astronomical surveys, automated methods of
analysis and classification of bulk data are a fundamental tool for fast and
efficient production of deliverables. This becomes ever more imminent as we
enter the Gaia era. We investigate the potential detectability of eclipsing
binaries with Gaia using a data set of all Kepler eclipsing binaries sampled
with Gaia cadence and folded with the Kepler period. The performance of fitting
methods is evaluated with comparison to real Kepler data parameters and a
classification scheme is proposed for the potentially detectable sources based
on the geometry of the light curve fits. The polynomial chain (polyfit) and
two-Gaussian models are used for light curve fitting of the data set.
Classification is performed with a combination of the t-SNE (t-distrubuted
Stochastic Neighbor Embedding) and DBSCAN (Density-Based Spatial Clustering of
Applications with Noise) algorithms. We find that approximately 68% of Kepler
Eclipsing Binary sources are potentially detectable by Gaia when folded with
the Kepler period and propose a classification scheme of the detectable sources
based on the morphological type indicative of the light curve, with subclasses
that reflect the properties of the fitted model (presence and visibility of
eclipses, their width, depth, etc.).Comment: 9 pages, 18 figures, accepted for publication in Astronomy &
Astrophysic
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