Relative efficiency of three mechanisms of vector field growth in a random media.

We consider a model of a random media with fixed and finite memory time with abrupt losses of memory (renovation model). Within the memory intervals we can observe either amplification or oscillation of the vector field in a given particle. The cumulative effect of amplifications in many subsequent intervals leads to amplification of the mean field and mean energy. Similarly, the cumulative effect of intermittent amplifications or oscillations also leads to amplification of the mean field and mean energy, however, at a lower rate. Finally, the random oscillations alone can resonate and yield the growth of the mean field and energy. These are the three mechanisms that we investigate and compute analytically and numerically the growth rates based on the Jacobi equation with a random curvature parameter.

Finite memory time and anisotropy effects for initial magnetic energy growth in random flow of conducting media.

The dynamo mechanism is a process of magnetic field self-excitation in a moving electrically conducting fluid. One of the most interesting applications of this mechanism related to the astrophysical systems is the case of a random motion of plasma. For the very first stage of the process, the governing dynamo equation can be reduced to a system of first-order ordinary differential equations. For this case we suggest a regular method to calculate the growth rate of magnetic energy. Based on this method we calculate the growth rate for random flow with finite memory time and anisotropic statistical distribution of the stretching matrix and compare the results with corresponding ones for the isotropic case and for short-correlated approximation. We find that for moderate Strouhal numbers and moderate anisotropy the analytical results reproduce the numerically estimated growth rates reasonably well, while for larger governing parameters the quantitative difference becomes substantial. In particular, analytical approximation is applicable for the Strouhal numbers s<0.6, and we find some numerical models and observational examples for which this region might be relevant. Rather unexpectedly, we find that the mirror asymmetry does not contribute to the growth rates obtained, although the mirror asymmetry effects are known to be crucial for later stages of dynamo action.

[Correlations between gynoecium morphology and ovary position in angiosperm flowers: roles of developmental and terminological constraints].

Angiosperm gynoecium consists of elementary units, called carpels. These can be free (apocarpy) or united (coenocarpy, or syncarpy in a wide sense). One of the most complicate problems of evolutionary morphology of angiosperms is distinguishing monomerous and pseudomonomerous gynoecia. The former are assumed to be derived by reduction of carpel number in apocarpous gynoecia, the latter by reduction of gynoecia with united carpels. Pseudomonomerous gynoecia have one fertile carpel and more or less prominent traces of sterile carpel(s). In extreme cases of reduction, pseudomonomerous gynoecia are very similar to monomerous, even though the two types have completely different evolutionary histories. G.B. Kedrov (1969) proposed a new approach to resolving the issue. Using the fact of absence of polymerous free-carpellate gynoecia with inferior ovaries, he suggested that there is a constraint against epigyny in plants with free carpels. Therefore, in taxa with disputable morphological interpretations, the gynoecium should be treated as pseudomonomerous (and not monomerous) if the ovary is inferior. A critical review of the concept of G.B. Kedrov showed that his ideas would suggest re-interpretation of widely accepted views on gynoecium morphology in several key families of basal angiosperms. An alternative view is proposed, that for most important types of epigyny in angiosperms, a "constraint" for a combination of inferior ovary and apocarpy is due to definition of the term "apocarpy" only. There is no biological sense in this "constraint". Existence of two other morphogenetic constraints is proposed: (1) against development of a typical inferior ovary in monomerous gynoecia with conduplicate carpel and (2) against a radial (sectorial) fusion of individual carpels with stamens or perianth members without fusion of these groups into an entire structure. Possible biological nature of these constraints is discussed.

Morphology and nrITS phylogeny of the genus Pinguicula L. (Lentibulariaceae), with special attention to embryo evolution.

The genus Pinguicula (Lentibulariaceae) is unusual within the dicot order Lamiales because of the occurrence of both embryos with two cotyledons and those with just one cotyledon. In order to elucidate the infrageneric relationships and the evolutionary history of the embryo, we analysed (1) the internal transcribed spacers ITS1 and ITS2 of the nuclear ribosomal DNA (nrITS) of 29 Old and New World taxa of Pinguicula, and (2) the morphological and anatomical characters of the seeds. We suggest that the cotyledon number and spermoderm structure were quite unstable in the evolution of Pinguicula. Although basal nodes of the nrITS tree are sensitive to taxon sampling, all tree topologies found in this study imply homoplasy in the cotyledon number.

Large-scale magnetic field generation by alpha effect driven by collective neutrino-plasma interaction.

We suggest a new mechanism for the generation of a large-scale magnetic field in the hot plasma of the early Universe which is based on parity violation in weak interactions and depends neither on the helicity of matter turbulence resulting in the standard alpha effect nor on general rotation. The mechanism can result in a self-excitation of an (almost) uniform cosmological magnetic field.

Mean-field theory for a passive scalar advected by a turbulent velocity field with a random renewal time.

Mean-field theory for turbulent transport of a passive scalar (e.g., particles and gases) is discussed. Equations for the mean number density of particles advected by a random velocity field, with a finite correlation time, are derived. Mean-field equations for a passive scalar comprise spatial derivatives of high orders due to the nonlocal nature of passive scalar transport in a random velocity field with a finite correlation time. A turbulent velocity field with a random renewal time is considered. This model is more realistic than that with a constant renewal time used by Elperin et al. [Phys. Rev. E 61, 2617 (2000)], and employs two characteristic times: the correlation time of a random velocity field tau(c), and a mean renewal time tau. It is demonstrated that the turbulent diffusion coefficient is determined by the minimum of the times tau(c) and tau. The mean-field equation for a passive scalar was derived for different ratios of tau/tau(c). The important role of the statistics of the field of Lagrangian trajectories in turbulent transport of a passive scalar, in a random velocity field with a finite correlation time, is demonstrated. It is shown that in the case tau(c)<

Strange behavior of a passive scalar in a linear velocity field.

Damping (or growth) rates of a typical realization, mean-field and high-order correlation functions of a passive scalar (e.g., a number density of particles) advected by a linear velocity fields are estimated. It is shown that all statistical moments higher than the first moment and a typical realization of a passive scalar without an external pumping decay for both laminar and random incompressible linear velocity fields. Strong compressibility of a laminar linear velocity field can result in a growth of a typical realization and the high-order moments of a passive scalar. It is demonstrated that for a laminar compressible linear velocity field the flux of particles from the infinity does not vanish and the total number of particles is not conserved. For a random compressible linear velocity field a typical realization decays whereas the high-order moments of a passive scalar can grow. Comparison of the obtained results with those for dynamics of a passive scalar advected by a homogeneous isotropic and compressible turbulent flow with a given longitudinal two-point correlation function F=1-r(2) is performed (where r is the distance between two points measured in the units of the maximum scale of turbulent motions).

Genetic control of ganglioside biosynthesis in mice.

The enzymatic basis for the differences in hepatic ganglioside patterns in the mouse strains C57Bl/6 and Swiss White (SW) was investigated. SW has a "Swiss-type" ganglioside profile, expressing GM1- and GD1a- in addition to GM2- as major hepatic gangliosides, whereas C57Bl/6 shows a "GM2-type" profile, expressing only GM2- as the major hepatic ganglioside. The enzyme UDP-galactose:GM2 ganglioside galactosyltransferase (GM2-GalT), which catalyzes the synthesis of GM1 ganglioside, showed a four- to fivefold elevation in intact and solubilized liver Golgi membrane fractions of the SW strain compared to C57Bl/6. Crosses between C57Bl/6 and SW produced an F1 generation with a hepatic ganglioside and enzymatic phenotype intermediate between those of the two parental strains. All three genotypic groups show two forms of the Golgi apparatus enzyme with isoelectric points of 6.5-6.8 and 8.3-9.0. The simplest mode of action of genes which control the enzymatic phenotype that would be consistent with these findings are one or two structural genes or one or two cis-regulatory genes affecting the rate of enzyme synthesis.

Self-excitation of a nonlinear scalar field in a random medium.

We discuss the evolution in time of a scalar field under the influence of a random potential and diffusion. The cases of a short-correlation in time and of stationary potentials are considered. In a linear approximation and for sufficiently weak diffusion, the statistical moments of the field grow exponentially in time at growth rates that progressively increase with the order of the moment; this indicates the intermittent nature of the field. Nonlinearity halts this growth and in some cases can destroy the intermittency. However, in many nonlinear situations the intermittency is preserved: high, persistent peaks of the field exist against the background of a smooth field distribution. These widely spaced peaks may make a major contribution to the average characteristics of the field.