8,490 research outputs found
The fitting of multifunctions : an approach to nonparametric multimodal regression.
In the last decades a lot of research has been devoted to
smoothing in the sense of nonparametric regression. However, this
work has nearly exclusively concentrated on fitting regression
functions. When the conditional distribution of y|x is
multimodal, the assumption of a functional relationship y = m(x)
+ noise might be too restrictive. We introduce a nonparametric
approach to fit multifunctions, allowing to assign a set of
output values to a given x. The concept is based on
conditional mean shift, which is an easily implemented tool to
detect the local maxima of a conditional density function. The
methodology is illustrated by environmental data examples
Classical and all-floating FETI methods for the simulation of arterial tissues
High-resolution and anatomically realistic computer models of biological soft
tissues play a significant role in the understanding of the function of
cardiovascular components in health and disease. However, the computational
effort to handle fine grids to resolve the geometries as well as sophisticated
tissue models is very challenging. One possibility to derive a strongly
scalable parallel solution algorithm is to consider finite element tearing and
interconnecting (FETI) methods. In this study we propose and investigate the
application of FETI methods to simulate the elastic behavior of biological soft
tissues. As one particular example we choose the artery which is - as most
other biological tissues - characterized by anisotropic and nonlinear material
properties. We compare two specific approaches of FETI methods, classical and
all-floating, and investigate the numerical behavior of different
preconditioning techniques. In comparison to classical FETI, the all-floating
approach has not only advantages concerning the implementation but in many
cases also concerning the convergence of the global iterative solution method.
This behavior is illustrated with numerical examples. We present results of
linear elastic simulations to show convergence rates, as expected from the
theory, and results from the more sophisticated nonlinear case where we apply a
well-known anisotropic model to the realistic geometry of an artery. Although
the FETI methods have a great applicability on artery simulations we will also
discuss some limitations concerning the dependence on material parameters.Comment: 29 page
Exact and Fast Numerical Algorithms for the Stochastic Wave Equation
On the basis of integral representations we propose fast numerical methods to solve the Cauchy problem for the stochastic wave equation without boundaries and with the Dirichlet boundary conditions. The algorithms are exact in a probabilistic sense
The planetary nebula population in the halo of M87
We investigate the diffuse light in the outer regions of the nearby
elliptical galaxy M87 in the Virgo cluster, using planetary nebulas (PNs) as
tracers. The surveyed areas (0.43 squared degrees) cover M87 up to a radial
distance of 150 kpc, in the ransition region between galaxy halo and
intracluster light (ICL). All PNs are identified through the on-off band
technique using automatic selection criteria based on the distribution of the
detected sources in the colour-magnitude diagram and the properties of their
point-spread function. We extract a catalogue of 688 objects down to
m_5007=28.4, with an estimated residual contamination from foreground stars and
background Lyalpha galaxies, which amounts to ~35% of the sample. This is one
of the largest extragalactic PN samples in number of candidates, magnitude
depth, and radial extent, which allows us to carry out an unprecedented
photometric study of the PN population in the outer regions of M87. We find
that the logarithmic density profile of the PN distribution is shallower than
the surface brightness profile at large radii. This behaviour is consistent
with the superposition of two components associated with the halo of M87 and
with the ICL, which have different luminosity specific PN numbers, the ICL
contributing three times more PNs per unit light. Because of the depth of this
survey we are also able to study the shape of the PN luminosity function (PNLF)
in the outer regions of M87. We find a slope for the PNLF that is steeper at
fainter magnitudes than the standard analytical PNLF formula and adopt a
generalised model that treats the slope as a free parameter. Comparing the PNLF
of M87 and the M31 bulge, both normalised by the sampled luminosity, the M87
PNLF contains fewer bright PNs and has a steeper slope towards fainter
magnitudes.Comment: 16 pages, 13 figures, 5 tables, accepted for publication in A&
Transition from antibunching to bunching in cavity QED
The photon statistics of the light emitted from an atomic ensemble into a
single field mode of an optical cavity is investigated as a function of the
number of atoms. The light is produced in a Raman transition driven by a pump
laser and the cavity vacuum [M.Hennrich et al., Phys. Rev. Lett. 85, 4672
(2000)], and a recycling laser is employed to repeat this process continuously.
For weak driving, a smooth transition from antibunching to bunching is found
for about one intra-cavity atom. Remarkably, the bunching peak develops within
the antibunching dip. For saturated driving and a growing number of atoms, the
bunching amplitude decreases and the bunching duration increases, indicating
the onset of Raman lasing.Comment: 4 pages, 4 figure
Detection, photometry and slitless radial velocities of 535 planetary nebulae in the flattened elliptical galaxy NGC 4697
We have detected 535 planetary nebulae (PNs) in NGC 4697, using the classic
on-band, off-band filter technique with the Focal Reducer and Spectrograph
(FORS) at the Cassegrain focus of the first 8-meter telescope unit of the ESO
Very Large Telescope. From our photometry we have built the [O III] 5007
planetary nebula luminosity function (PNLF) of NGC 4697. It indicates a
distance of 10.5 Mpc, substantially smaller than a previous estimate of 24 Mpc
used in earlier dynamical studies. The PNLF also provides an estimate of the
specific PN formation rate. Combining the information from on-band images with
PN positions on dispersed, slitless grism images, we have obtained radial
velocities for 531 of the 535 PNs. They provide kinematic information up to a
distance of almost three effective radii from the nucleus. Some rotation is
detected in the outer regions, but the rotation curve of this galaxy appears to
drop beyond one effective radius. Assuming an isotropic velocity distribution,
the velocity dispersion profile is consistent with no dark matter within three
effective radii of the nucleus (however, some dark matter can be present if the
velocity distribution is anisotropic). We obtain a blue mass-to-light ratio of
11. Earlier M/L ratios for NGC 4697 were too small, because of the too large
distance used for their derivation.Comment: 52 pages, 24 Postscript figures, ApJ 2001, in pres
The stellar dynamics and mass of NGC 1316 using the radial velocities of planetary nebulae
We present a study of the kinematics of the outer regions of the early-type
galaxy NGC 1316, based on radial velocity measurements of 43 planetary nebulae
as well as deep integrated-light absorption line spectra. The smoothed velocity
field of NGC 1316 indicates fast rotation at a distance of 16 kpc, possibly
associated with an elongated feature orthogonal to the inner dust lanes. The
mean square stellar velocity is approximately independent of radius, and the
estimated total mass of the system is 2.6 x 10^11 M_sun within a radius of 16
kpc, implying an integrated mass-to-light ratio of M/L_B = 8.Comment: 39 pages, 14 figures, in press on The Astrophysical Journal n. 50
Infinite compressibility states in the Hierarchical Reference Theory of fluids. II. Numerical evidence
Continuing our investigation into the Hierarchical Reference Theory of fluids
for thermodynamic states of infinite isothermal compressibility kappa[T] we now
turn to the available numerical evidence to elucidate the character of the
partial differential equation: Of the three scenarios identified previously,
only the assumption of the equations turning stiff when building up the
divergence of kappa[T] allows for a satisfactory interpretation of the data. In
addition to the asymptotic regime where the arguments of part I
(cond-mat/0308467) directly apply, a similar mechanism is identified that gives
rise to transient stiffness at intermediate cutoff for low enough temperature.
Heuristic arguments point to a connection between the form of the Fourier
transform of the perturbational part of the interaction potential and the
cutoff where finite difference approximations of the differential equation
cease to be applicable, and they highlight the rather special standing of the
hard-core Yukawa potential as regards the severity of the computational
difficulties.Comment: J. Stat. Phys., in press. Minor changes to match published versio
From algebra to logic: there and back again -- the story of a hierarchy
This is an extended survey of the results concerning a hierarchy of languages
that is tightly connected with the quantifier alternation hierarchy within the
two-variable fragment of first order logic of the linear order.Comment: Developments in Language Theory 2014, Ekaterinburg : Russian
Federation (2014
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