4,459 research outputs found
Efficient estimation of AUC in a sliding window
In many applications, monitoring area under the ROC curve (AUC) in a sliding
window over a data stream is a natural way of detecting changes in the system.
The drawback is that computing AUC in a sliding window is expensive, especially
if the window size is large and the data flow is significant.
In this paper we propose a scheme for maintaining an approximate AUC in a
sliding window of length . More specifically, we propose an algorithm that,
given , estimates AUC within , and can maintain this
estimate in time, per update, as the window slides.
This provides a speed-up over the exact computation of AUC, which requires
time, per update. The speed-up becomes more significant as the size of
the window increases. Our estimate is based on grouping the data points
together, and using these groups to calculate AUC. The grouping is designed
carefully such that () the groups are small enough, so that the error stays
small, () the number of groups is small, so that enumerating them is not
expensive, and () the definition is flexible enough so that we can
maintain the groups efficiently.
Our experimental evaluation demonstrates that the average approximation error
in practice is much smaller than the approximation guarantee ,
and that we can achieve significant speed-ups with only a modest sacrifice in
accuracy
The application of interactive graphics to large time-dependent hydrodynamics problems
A written companion of a movie entitled "Interactive Graphics at Los Alamos Scientific Laboratory" was presented. While the movie presents the actual graphics terminal and the functions performed on it, the paper attempts to put in perspective the complexity of the application code and the complexity of the interaction that is possible
CO observations and investigation of triggered star formation towards N10 infrared bubble and surroundings
We studied the environment of the dust bubble N10 in molecular emission.
Infrared bubbles, first detected by the GLIMPSE survey at 8.0 m, are ideal
regions to investigate the effect of the expansion of the HII region on its
surroundings eventual triggered star formation at its borders. In this work, we
present a multi-wavelength study of N10. This bubble is especially interesting
as infrared studies of the young stellar content suggest a scenario of ongoing
star formation, possibly triggered, on the edge of the HII region. We carried
out observations of CO(1-0) and CO(1-0) emission at PMO 13.7-m
towards N10. We also analyzed the IR and sub-mm emission on this region and
compare those different tracers to obtain a detailed view of the interaction
between the expanding HII region and the molecular gas. We also estimated the
parameters of the denser cold dust condensation and of the ionized gas inside
the shell. Bright CO emission was detected and two molecular clumps were
identified, from which we have derived physical parameters. We also estimate
the parameters for the densest cold dust condensation and for the ionized gas
inside the shell. The comparison between the dynamical age of this region and
the fragmentation time scale favors the "Radiation-Driven Implosion" mechanism
of star formation. N10 reveals to be specially interesting case with gas
structures in a narrow frontier between HII region and surrounding molecular
material, and with a range of ages of YSOs situated in region indicating
triggered star formation.Comment: Version 2 - Submmited to ApJ (under review
Interaction of colloids with a nematic-isotropic interface
The Landau-de Gennes free energy is used to calculate the interaction between
long cylindrical colloids and the nematic-isotropic (NI) interface. This
interaction has two contributions: one is specific of liquid crystals and
results from the deformation of the director field close to the particles or to
the interface, while the other is generic and results from wetting and surface
tension effects.
Deep in the nematic phase the director field of long cylindrical colloids,
with strong homeotropic anchoring, exhibits two half-integer defect lines. As
the colloid moves towards the interface, the director configuration changes
through a series of discontinuous transitions, where one or two of the defects
are annihilated. In addition, the NI interface bends towards the colloid in
order to minimize the elastic free energy in the nematic. In the isotropic
phase, the colloid is surrounded by a thin nematic layer that reduces the
surface free energy under favorable wetting conditions.
The interaction has a well-defined minimum near the interface. In this region
the director and interfacial structures are complex and cannot be described
analytically. Using the numerical results for the Landau-de Gennes free energy
in the harmonic region, we obtained simple scaling laws for the (linear) force
on the colloid
Magnetic Field Dependent Behavior of the CDW ground state in Per2M(mnt)2 (M = Au, Pt)
The Per2M(mnt)2 class of organic conductors exhibit a charge density wave
(CDW) ground state below about 12 K, which may be suppressed in magnetic fields
of order 20 to 30 T. However, for both cases of counter ion M(mnt)2 species
studied (M = Au (zero spin) and M = Pt (spin 1/2)), new high field ground
states evolve for further increases in magnetic field. We report recent
investigations where thermopower, Hall effect, high pressure and additional
transport measurements have been carried out to explore these new high field
phases.Comment: 6 pages, 10 figures, 27 reference
The effect of polydispersity on the ordering transition of adsorbed self-assembled rigid rods
Extensive Monte Carlo simulations were carried out to investigate the nature
of the ordering transition of a model of adsorbed self-assembled rigid rods on
the bonds of a square lattice [Tavares et. al., Phys. Rev E 79, 021505 (2009)].
The polydisperse rods undergo a continuous ordering transition that is found to
be in the two-dimensional Ising universality class, as in models where the rods
are monodisperse. This finding is in sharp contrast with the recent claim that
equilibrium polydispersity changes the nature of the phase transition in this
class of models [L`opez et. al., Phys. Rev E 80, 040105(R)(2009)].Comment: 19 pages, 5 figure
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