819 research outputs found
Global wellposedness for a certain class of large initial data for the 3D Navier-Stokes Equations
In this article, we consider a special class of initial data to the 3D
Navier-Stokes equations on the torus, in which there is a certain degree of
orthogonality in the components of the initial data. We showed that, under such
conditions, the Navier-Stokes equations are globally wellposed. We also showed
that there exists large initial data, in the sense of the critical norm
that satisfies the conditions that we considered.Comment: 13 pages, updated references for v
Global wellposed problem for the 3-D incompressible anisotropic Navier-Stokes equations
In this paper, we consider a global wellposed problem for the 3-D
incompressible anisotropic Navier-Stokes equations (\textit{ANS}). In order to
do so, we first introduce the scaling invariant Besov-Sobolev type spaces,
and , .
Then, we prove the global wellposedness for (\textit{ANS}) provided the initial
data are sufficient small compared to the horizontal viscosity in some suitable
sense, which is stronger than norm. In
particular, our results imply the global wellposedness of (\textit{ANS}) with
high oscillatory initial data.Comment: 39 page
Globular clusters and dwarf galaxies in Fornax - I. Kinematics in the cluster core from multi-object spectroscopy
We acquired radial velocities of a significant number of globular clusters
(GCs) on wide fields between galaxies in the nearby Fornax cluster of galaxies,
in order to derive their velocity dispersion radial profile and to probe the
dynamics of the cluster. We used FLAMES on the VLT to obtain accurate
velocities for 149 GCs, within a ~500x150 kpc strip centered on NGC 1399, the
Fornax central galaxy. These objects are at the very bright tail (M_V < -9.5)
of the GC luminosity function, overlapping the so-called ``ultra-compact
dwarfs'' magnitude range. Eight of the brightest FLAMES-confirmed members
indeed show hints of resolution in the subarcsecond pre-imaging data we used
for selecting the ~500 targets for FLAMES spectroscopy. Ignoring the GCs around
galaxies by applying 3d_25 diameter masks, we find 61 GCs of 20.0 < V < 22.2
lying in the intra-cluster (IC) medium. The velocity dispersion of the
population of ICGCs is 200 km/s at ~150 kpc from the central NGC 1399 and rises
to nearly 400 km/s at 200 kpc, a value which compares with the velocity
dispersion of the population of dwarf galaxies, thought to be infalling from
the surroundings of the cluster.Comment: To be published in A&A Letters. 4 pages, 3 figures, 3 table
Global well-posedness for a Smoluchowski equation coupled with Navier-Stokes equations in 2D
We prove global existence for a nonlinear Smoluchowski equation (a nonlinear
Fokker-Planck equation) coupled with Navier-Stokes equations in two dimensions.
The proof uses a deteriorating regularity estimate and the tensorial structure
of the main nonlinear terms
Extended HI Rotation Curve and Mass Distribution of M31
New HI observations of Messier 31 (M31) obtained with the Effelsberg and
Green Bank 100-m telescopes make it possible to measure the rotation curve of
that galaxy out to ~35 kpc. Between 20 and 35 kpc, the rotation curve is nearly
flat at a velocity of ~226 km/s. A model of the mass distribution shows that at
the last observed velocity point, the minimum dark-to-luminous mass ratio is
\~0.5 for a total mass of 3.4 10^11 Msol at R < 35 kpc. This can be compared to
the estimated MW mass of 4.9 10^11 Msol for R < 50 kpc.Comment: 4 pages, 2 figures, accepted for publication in ApJ Letter
Stellar mass map and dark matter distribution in M31
Stellar mass distribution in M31 is estimated using optical and infrared
imaging data. Combining the derived stellar mass model with various kinematical
data, properties of the DM halo of the galaxy are constrained.
SDSS observations through the ugriz filters and the Spitzer imaging at 3.6
microns are used to sample the SED of the galaxy at each imaging pixel.
Intrinsic dust extinction effects are taken into account by using far-infrared
observations. Synthetic SEDs created with different stellar population
synthesis models are fitted to the observed SEDs, providing estimates for the
stellar mass surface density. The stellar mass distribution of the galaxy is
described with a 3D model consisting of a nucleus, a bulge, a disc, a young
disc and a halo component, each following the Einasto density distribution
(relations between different functional forms of the Einasto density
distribution are given in App. B). By comparing the stellar mass distribution
to the observed rotation curve and kinematics of outer globular clusters and
satellite galaxies, the DM halo parameters are estimated.
Stellar population synthesis models suggest that M31 is dominated by old
stars throughout the galaxy. The total stellar mass is (10-15)10^10Msun, 30% of
which is in the bulge and 56% in the disc. None of the tested DM distribution
models can be falsified on the basis of the stellar matter distribution and the
rotation curve of the galaxy. The virial mass of the DM halo is
(0.8-1.1)10^12Msun and the virial radius is 189-213kpc, depending on the DM
distribution. The central density of the DM halo is comparable to that of
nearby dwarf galaxies, low-surface-brightness galaxies and distant massive disc
galaxies, thus the evolution of central DM halo properties seems to be
regulated by similar processes for a broad range of halo masses, environments,
and cosmological epochs.Comment: 11 pages, 13 figures, 6 tables, accepted for publication in Astronomy
and Astrophysic
Global well-posedness issues for the inviscid Boussinesq system with Yudovich's type data
The present paper is dedicated to the study of the global existence for the
inviscid two-dimensional Boussinesq system. We focus on finite energy data with
bounded vorticity and we find out that, under quite a natural additional
assumption on the initial temperature, there exists a global unique solution.
None smallness conditions are imposed on the data. The global existence issues
for infinite energy initial velocity, and for the B\'enard system are also
discussed.Comment: 12 page
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