2,195 research outputs found
On spherically symmetrical accretion in fractal media
We use fractional integrals to generalize the description of hydrodynamic
accretion in fractal media. The fractional continuous medium model allows the
generalization of the equations of balance of mass density and momentum
density. These make it possible to consider the general case of spherical
hydrodynamic accretion onto a gravitating mass embedded in a fractal medium.
The general nature of the solution is similar to the "Bondi solution", but the
accretion rate may vary substantially and the dependence on central mass may
change significantly depending on dimensionality of the fractal medium. The
theory shows consistency with the observational data and numerical simulation
results for the particular case of accretion onto pre-main-sequence stars.Comment: 5 pages, 2 figures. Accepted for publication in MNRAS Letters. The
definitive version is available at http://www.blackwell-synergy.co
Interaction effects in assembly of magnetic nanoparticles
A specific absorption rate of a dilute assembly of various random clusters of
iron oxide nanoparticles in alternating magnetic field has been calculated
using Landau- Lifshitz stochastic equation. This approach simultaneously takes
into account both the presence of thermal fluctuations of the nanoparticle
magnetic moments, and magneto-dipole interaction between the nanoparticles of
the clusters. It is shown that for usual 3D clusters the intensity of magneto-
dipole interaction is determined mainly by the cluster packing density eta =
Np*V/Vcl, where Np is the average number of the particles in the cluster, V is
the nanoparticle volume, and Vcl is the cluster volume. The area of the low
frequency hysteresis loop and the assembly specific absorption rate have been
found to be considerably reduced when the packing density of the clusters
increases in the range of 0.005 < eta < 0.4. The dependence of the specific
absorption rate on the mean nanoparticle diameter is retained with increase of
eta, but becomes less pronounced. For fractal clusters of nanoparticles, which
arise in biological media, in addition to considerable reduction of the
absorption rate, the absorption maximum is shifted to smaller particle
diameters. It is found also that the specific absorption rate of fractal
clusters increases appreciably with increase of the thickness of nonmagnetic
shells at the nanoparticle surfaces.Comment: The paper is accepted for Nanoscale Res. Let
Transport Equations from Liouville Equations for Fractional Systems
We consider dynamical systems that are described by fractional power of
coordinates and momenta. The fractional powers can be considered as a
convenient way to describe systems in the fractional dimension space. For the
usual space the fractional systems are non-Hamiltonian. Generalized transport
equation is derived from Liouville and Bogoliubov equations for fractional
systems. Fractional generalization of average values and reduced distribution
functions are defined. Hydrodynamic equations for fractional systems are
derived from the generalized transport equation.Comment: 11 pages, LaTe
The Quest for the Heaviest Uranium Isotope
We study Uranium isotopes and surrounding elements at very large neutron
number excess. Relativistic mean field and Skyrme-type approaches with
different parametrizations are used in the study. Most models show clear
indications for isotopes that are stable with respect to neutron emission far
beyond N=184 up to the range of around N=258.Comment: 4 pages, 5. figure
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