892,209 research outputs found
A maximum principle in spectral optimization problems for elliptic operators subject to mass density perturbations
We consider eigenvalue problems for general elliptic operators of arbitrary
order subject to homogeneous boundary conditions on open subsets of the
euclidean N-dimensional space. We prove stability results for the dependence of
the eigenvalues upon variation of the mass density and we prove a maximum
principle for extremum problems related to mass density perturbations which
preserve the total mass
Evolution models for mass transportation problems
We present a survey on several mass transportation problems, in which a given
mass dynamically moves from an initial configuration to a final one. The
approach we consider is the one introduced by Benamou and Brenier in [5], where
a suitable cost functional , depending on the density and on
the velocity (which fulfill the continuity equation), has to be minimized.
Acting on the functional various forms of mass transportation problems can
be modeled, as for instance those presenting congestion effects, occurring in
traffic simulations and in crowd motions, or concentration effects, which give
rise to branched structures.Comment: 16 pages, 14 figures; Milan J. Math., (2012
Lower mass limit of an evolving interstellar cloud and chemistry in an evolving oscillatory cloud
Simultaneous solution of the equation of motion, equation of state and energy equation including heating and cooling processes for interstellar medium gives for a collapsing cloud a lower mass limit which is significantly smaller than the Jeans mass for the same initial density. The clouds with higher mass than this limiting mass collapse whereas clouds with smaller than critical mass pass through a maximum central density giving apparently similar clouds (i.e., same Av, size and central density) at two different phases of its evolution (i.e., with different life time). Preliminary results of chemistry in such an evolving oscillatory cloud show significant difference in abundances of some of the molecules in two physically similar clouds with different life times. The problems of depletion and short life time of evolving clouds appear to be less severe in such an oscillatory cloud
The halo mass function conditioned on density from the Millennium Simulation: insights into missing baryons and galaxy mass functions
The baryon content of high-density regions in the universe is relevant to two
critical unanswered questions: the workings of nurture effects on galaxies and
the whereabouts of the missing baryons. In this paper, we analyze the
distribution of dark matter and semianalytical galaxies in the Millennium
Simulation to investigate these problems. Applying the same density field
reconstruction schemes as used for the overall matter distribution to the
matter locked in halos we study the mass contribution of halos to the total
mass budget at various background field densities, i.e., the conditional halo
mass function. In this context, we present a simple fitting formula for the
cumulative mass function accurate to ~ 5% for halo masses between 10^{10} and
10^{15}Msol/h. We find that in dense environments the halo mass function
becomes top heavy and present corresponding fitting formulae for different
redshifts. We demonstrate that the major fraction of matter in high-density
fields is associated with galaxy groups. Since current X-ray surveys are able
to nearly recover the universal baryon fraction within groups, our results
indicate that the major part of the so-far undetected warm-hot intergalactic
medium resides in low-density regions at low temperatures. Similarly, we show
that the differences in galaxy mass functions with environment seen in observed
and simulated data stem predominantly from differences in the mass distribution
of halos. In particular, the hump in the galaxy mass function is associated
with the central group galaxies, and the bimodality observed in the galaxy mass
function is therefore interpreted as that of central galaxies versus
satellites.Comment: aligned with version published in Ap
Boson Stars from Self-Interacting Dark Matter
We study the possibility that self-interacting bosonic dark matter forms
star-like objects. We study both the case of attractive and repulsive
self-interactions, and we focus particularly in the parameter phase space where
self-interactions can solve well standing problems of the collisionless dark
matter paradigm. We find the mass radius relations for these dark matter
bosonic stars, their density profile as well as the maximum mass they can
support.Comment: 12 pages, 6 figures; references adde
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