Destruction of the family of steady states in the planar problem of Darcy convection

The natural convection of incompressible fluid in a porous medium causes for some boundary conditions a strong non-uniqueness in the form of a continuous family of steady states. We are interested in the situation when these boundary conditions are violated. The resulting destruction of the family of steady states is studied via computer experiments based on a mimetic finite-difference approach. Convection in a rectangular enclosure is considered under different perturbations of boundary conditions (heat sources, infiltration). Two scenario of the family of equilibria are found: the transformation to a limit cycle and the formation of isolated convective patterns.Comment: 12 pages, 6 figure

Використання моделі раннього ембріонального розвитку перепела японського (coturnix coturnix japonica) для оцінки біологічної активності мікрохвильового випромінювання

During the last few decades, worldwide intensive implementation of GSM mobile communication systems has occurred. Recent epidemiological studies raised concerns about potential hazards of long-term microwave exposure for human health. We aimed at assessment of biological effects of microwave emitted by commercial cell phone using developing bird embryo as a model. Embryos of Japanese Quails were exposed in ovo to GSM 900 MHz cellular phone radiation during initial 38 h of brooding or alternatively during 158 h (120 h before brooding plus initial 38 h of brooding) discontinuously with 48 sec ON followed by 12 sec OFF intervals. Maximum intensity of incident radiation on the egg’s surface was 0,2 µW/cm2. A number of differentiated somiteswere assessed microscopically. Possible DNA damage evoked by irradiation was assessed by an alkaline comet assay. Exposure to radiation from GSM 900 MHz cellular phone led to a significantly altered number of differentiated somites. In embryos irradiated during 38 h the number of differentiated somitesincreased (p<0,001), while in embryos irradiated during 158 h this number decreased (p<0.05). The lower duration of exposure led to significant (p<0.001) decrease in a level of DNA stand breaks in cells of 38-h embryos, while the higher duration of exposure resulted in a significant (p<0.001) increase in DNA damage as compared to the control.У роботі на моделі перепелиного ембріона продемонстровано високу чутливість моделі раннього ембріогенезу перепелів до низькоінтенсивного мікрохвильового випромінювання, що проявляється в стимуляції або пригніченні сомітогенезу та зміні рівня ушкодження ДНК у клітинах 38-годинних ембріонів

Staggered grids discretization in three-dimensional Darcy convection

We consider three-dimensional convection of an incompressible fluid saturated in a parallelepiped with a porous medium. A mimetic finite-difference scheme for the Darcy convection problem in the primitive variables is developed. It consists of staggered nonuniform grids with five types of nodes, differencing and averaging operators on a two-nodes stencil. The nonlinear terms are approximated using special schemes. Two problems with different boundary conditions are considered to study scenarios of instability of the state of rest. Branching off of a continuous family of steady states was detected for the problem with zero heat fluxes on two opposite lateral planes.Comment: 20 pages, 9 figure

High order accuracy scheme for modeling the dynamics of predator and prey in heterogeneous environment

The aim of this work is to develop a compact finite-difference approach for modeling the dynamics of predator and prey based on reaction-diffusion-advection equations with variable coefficients. Methods. To discretize a spatially inhomogeneous problem with nonlinear terms of taxis and local interaction, the balance method is used. Species densities are determined on the main grid whereas fluxes are computed at the nodes of the staggered grid. Integration over time is carried out using the high-order Runge-Kutta method. Results. For the case of one-dimensional annular interval, the finite-difference scheme on the three-point stencil has been constructed that makes it possible to increase the order of accuracy compared to the standard second-order approximation scheme. The results of computational experiment are presented and comparison of schemes for stationary and non-stationary solutions is carried out. We conduct the calculation of accuracy order basing on the Aitken process for sequences of spatial grids. The calculated values of the effective order accuracy for the proposed scheme were greater than the standard two: for the diffusion problem, values of at least four were obtained. Decrease was obtained when directional migration was taken into account. This conclusion was also confirmed for non-stationary oscillatory regimes. Conclusion. The results demonstrate the effectiveness of the derived scheme for dynamics of predator and prey system in a heterogeneous environment

Oxidative and mutagenic effects of low intensity microwave radiation on quail embryos

Intensive implementation of wireless communication systems raised the question of the possible adverse effects of anthropogenic electromagnetic radiation. This study aims to assess the biological effects of low intensity microwaves (MW) radiation from smartphone Huawei Y5I commercial model used alone or in combination with attached Waveex chip that balances low frequency electromagnetic field but does not affect microwave signal. The biological model of developing quail embryos in ovo was used in the study. The phone as a source of low intensity 1800 MHz (0.32 µW/cm2) microwaves radiation was placed at 3 cm over the surface of hatching eggs and discontinuously activated with a computer program (48 s – on, 12 s – off). It was demonstrated that the exposure of quail embryos to radiation resulted in a statistically significant increase in the content of superoxide, nitrogen oxide and TBA products, DNA integrity damage in embryo cells and increased embryo mortality. Application of Waveex chip during the exposure resulted in a partial normalization of oxidative status and DNA integrity in embryonic cells indicating a negative impact not only of MW radiation, but of low-frequency electromagnetic fields from mobile devices as well

“Buttressing Effect” in the Halogen‐Lithium Exchange in ortho‐Bromo‐N,N‐dimethylanilines and Related Naphthalenes

Non-covalent interactions such as coordination of an organolithium reagent by a directing group and steric repulsion of substituents strongly affect the halogen-lithium exchange process. Here we present the manifestation of the “buttressing effect” – an indirect interaction between two substituents issued by the presence of a third group – and its influence on the ease and selectivity of the bromine-lithium exchange and the reactivity of formed aryllithiums. The increase of the size of the “buttressing” substituent strongly affects the conformation of a NMe2 group, forcing it to hinder ortho-bromine and thus slowing down the exchange. In naphthalene substrates bearing two bromines, this suppresses regioselectivity of the reaction. The “buttressing effect” forces formed aryllithiums to deaggregate, thus boosting their reactivity. This facilitates the decomposition via protolisys by ethereal solvents even at low temperatures and in some cases initiates fast Wurtz-Fittig coupling

Вплив мікрохвильового випромінювання на стан антиоксидантної системи в тканинах перепелиних ембріонів та добового молодняку

Long-term exposure of humans to low intensity radiofrequency electromagnetic radiation (RF-EMR) leads to a statistically significant increase in tumor incidence. Mechanisms of such the effects are unclear, but features of oxidative stress in living cells under RF-EMR exposure were previously reported. The aim of our study was to investigate the effect of microwave radiation on the state of the antioxidant system in the tissues of embryo and daily quail. Embryos of Japanese quails were exposed in ovo to extremely low intensity RF-EMR of GSM 900 MHz (14 μW/cm2) during 158–456 h discontinuously (48 c – ON, 12 c – OFF) before and in the initial stages of development. Significant oxidative effect of microwave radiation on the model of quail embryos was demonstrated. The effect was manifested in increased level of lipid peroxidation and decreased activity of key enzymes of antioxidant system.У роботі на моделі перепелиного ембріона продемонстровано достовірний оксидативний ефект мікрохвильового випромінювання, який проявлявся у вираженому зростанні рівня перекисного окиснення ліпідів і зниженні активності ключових ферментів антиоксидантної системи живих клітин

Cosymmetry preserving finite-difference methods for convection equations in a porous medium

The finite-difference discretizations for the planar problem of natural convection of incompressible fluid in a porous medium which preserve the cosymmetry property and discrete symmetries are presented. The equations in stream function and temperature are computed using staggered and non-staggered schemes in uniform and nonuniform rectangular grids. (c) 2004 IMACS. Published by Elsevier B.V. All rights reserved