945 research outputs found
Some biological features of Saprolegnia parasitica Coker - cause of fish dermatomycosis. [Translation from: Pervaya nauchnaya konferentsiya molodykh Uchenykh Biologov (Tezisy Dokladov) pp.84-86. Kiev, A.N.Ukr. SSR., 1964]
Parasitic and infectious diseases of fish, of wide distribution in fish-rearing ponds, retard to a significant extent the development of fish culture in the Ukraine. One of the diseases of fish attracting attention in connection with the general distribution of its causative agent, the fungus Saprolegnia parasitica Coker, in water-bodies of various types, appears to be dermatomycosis. The aim of this investigation is to study the conditions favouring the development of S. parasitica. Among the studied factors were water temperature and oxygen content
Model C critical dynamics of random anisotropy magnets
We study the relaxational critical dynamics of the three-dimensional random
anisotropy magnets with the non-conserved n-component order parameter coupled
to a conserved scalar density. In the random anisotropy magnets the structural
disorder is present in a form of local quenched anisotropy axes of random
orientation. When the anisotropy axes are randomly distributed along the edges
of the n-dimensional hypercube, asymptotical dynamical critical properties
coincide with those of the random-site Ising model. However structural disorder
gives rise to considerable effects for non-asymptotic critical dynamics. We
investigate this phenomenon by a field-theoretical renormalization group
analysis in the two-loop order. We study critical slowing down and obtain
quantitative estimates for the effective and asymptotic critical exponents of
the order parameter and scalar density. The results predict complex scenarios
for the effective critical exponent approaching an asymptotic regime.Comment: 8 figures, style files include
Phase Transition in the Random Anisotropy Model
The influence of a local anisotropy of random orientation on a ferromagnetic
phase transition is studied for two cases of anisotropy axis distribution. To
this end a model of a random anisotropy magnet is analyzed by means of the
field theoretical renormalization group approach in two loop approximation
refined by a resummation of the asymptotic series. The one-loop result of
Aharony indicating the absence of a second-order phase transition for an
isotropic distribution of random anisotropy axis at space dimension is
corroborated. For a cubic distribution the accessible stable fixed point leads
to disordered Ising-like critical exponents.Comment: 10 pages, 2 latex figures and a style file include
Monte-Carlo study of anisotropic scaling generated by disorder
We analyze the critical properties of the three-dimensional Ising model with
linear parallel extended defects. Such a form of disorder produces two distinct
correlation lengths, a parallel correlation length in the
direction along defects, and a perpendicular correlation length in
the direction perpendicular to the lines. Both and
diverge algebraically in the vicinity of the critical point, but the
corresponding critical exponents and take different
values. This property is specific for anisotropic scaling and the ratio
defines the anisotropy exponent . Estimates
of quantitative characteristics of the critical behaviour for such systems were
only obtained up to now within the renormalization group approach. We report a
study of the anisotropic scaling in this system via Monte Carlo simulation of
the three-dimensional system with Ising spins and non-magnetic impurities
arranged into randomly distributed parallel lines. Several independent
estimates for the anisotropy exponent of the system are obtained, as
well as an estimate of the susceptibility exponent . Our results
corroborate the renormalization group predictions obtained earlier.Comment: 22 pages, 9 figure
Phase behaviour and structure of a superionic liquid in nonpolarized nanoconfinement
The ion-ion interactions become exponentially screened for ions confined in
ultranarrow metallic pores. To study the phase behaviour of an assembly of such
ions, called a superionic liquid, we develop a statistical theory formulated on
bipartite lattices, which allows an analytical solution within the
Bethe-lattice approach. Our solution predicts the existence of ordered and
disordered phases in which ions form a crystal-like structure and a homogeneous
mixture, respectively. The transition between these two phases can potentially
be first or second order, depending on the ion diameter, degree of confinement
and pore ionophobicity. We supplement our analytical results by
three-dimensional off-lattice Monte Carlo simulations of an ionic liquid in
slit nanopores. The simulations predict formation of ionic clusters and ordered
snake-like patterns, leading to characteristic close-standing peaks in the
cation-cation and anion-anion radial distribution functions
Critical slowing down in random anisotropy magnets
We study the purely relaxational critical dynamics with non-conserved order
parameter (model A critical dynamics) for three-dimensional magnets with
disorder in a form of the random anisotropy axis. For the random axis
anisotropic distribution, the static asymptotic critical behaviour coincides
with that of random site Ising systems. Therefore the asymptotic critical
dynamics is governed by the dynamical exponent of the random Ising model.
However, the disorder influences considerably the dynamical behaviour in the
non-asymptotic regime. We perform a field-theoretical renormalization group
analysis within the minimal subtraction scheme in two-loop approximation to
investigate asymptotic and effective critical dynamics of random anisotropy
systems. The results demonstrate the non-monotonic behaviour of the dynamical
effective critical exponent .Comment: 11 pages, 4 figures, style file include
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