Parametric analysis of the ratio-dependent predator–prey model

We present a complete parametric analysis of stability properties and dynamic regimes of an ODE model in which the functional response is a function of the ratio of prey and predator abundances. We show the existence of eight qualitatively different types of system behaviors realized for various parameter values. In particular, there exist areas of coexistence (which may be steady or oscillating), areas in which both populations become extinct, and areas of "conditional coexistence" depending on the initial values. One of the main mathematical features of ratio-dependent models, distinguishing this class from other predator-prey models, is that the Origin is a complicated equilibrium point, whose characteristics crucially determine the main properties of the model. This is the first demonstration of this phenomenon in an ecological model. The model is investigated with methods of the qualitative theory of ODEs and the theory of bifurcations. The biological relevance of the mathematical results is discussed both regarding conservation issues (for which coexistence is desired) and biological control (for which extinction is desired).     

L1 (LINE-1) retrotransposable elements provide a "fossil" record of the phylogenetic history of murid rodents

The single most difficult problem in phylogenetic analysis is decidingwhether a shared taxonomic character is due to common ancestry or one thatappeared independently due to convergence, parallelism, or reversion to anancestral state. Mammalian L1 retrotransposons undergo periodicamplifications in which multiple copies of the elements are interspersed inthe genome. Because these elements apparently are transmitted only byinheritance and are retained in the genome, a shared L1 amplification eventcan only be an inherited ancestral character. We propose that L1amplification events can be an excellent tool for analyzing mammalianevolution and demonstrate here how we addressed several refractory problemsin rodent systematics using L1 DNA as a taxonomic character.     

On the Asymptotic Behaviour of the Population Number

We consider the stochastic model of an asexual population in which the number of couples formed in some generation is random variable depending on the number of individuals in that generation only. The conditions of convergence were obtained almost everywhere and in mean square of the normalized number of individuals in the n-th generation. These results may be considered as the generalization of some known statements about the models constructed on the basis of the branching processses theory.     

The influence of a magnetic field on chromosome sets and cell division]

An effect of stable magnetic field on karyotype and cell division of human lymphocytes from peripheral blood was studied in tissue culture. Comparative investigations were carried out with lymphocytes, whoch were treated with magnetic field of different tension (0,179; 0,391 and 0,600 Ts) and continuance (30 sec, 30 and 60 min). Lymphocytes, treated with stable magnetic field, were suspended in donor plasma and immediately cultivated after the treatment. The stable magnetic field was found to have a distinct mutagenic effect on cultivated lymphocytes of human peripheral blood. The increase in structural impairements of chromosomes correlated with tension of magnetic field and continuance of its effect. In structural impairements of chromosomes the chromatid gaps and breaks were more often observed but chromosome ruptures and pericentric clearances occurred more rarely. The effect of stable magnetic field on lymphocytes proliferation was studie. Under weak and transient using of magnetic field the proliferation was stimulated, but in rigid conditions--mitosis and blastic transformation were decreased. Continuous effect of magnetic field with weak tension did not inhibite the blastic transformation but influenced on the survival rate of cells in tissue culture, enhancing their lethality.     

A Method for Chronic Registration of Brain Cortical Electrical Activity in Rats

Journal of Evolutionary Biochemistry and Physiology - Electrocorticogram registration and analysis (electrocorticography, ECoG) is widely used in small-animal biomedical research. To date, a...     

Mathematical modeling of tumor therapy with oncolytic viruses: Regimes with complete tumor elimination within the framework of deterministic models

Background  

Oncolytic viruses that specifically target tumor cells are promising anti-cancer therapeutic agents. The interaction between an oncolytic virus and tumor cells is amenable to mathematical modeling using adaptations of techniques employed previously for modeling other types of virus-cell interaction.     

Metallic endoprostheses in the treatment of benign strictures of the biliary tract

Nine original nitinol self-smoothing-out stents and 3 Gianturco stents were implanted to treat benign strictures of biliary ducts and biliodigestive anastomosis after ineffective repeated attempts to make balloon dilatation. There were no complications associated with the implantation procedure. The follow-up of patients varied from 3 to 26 months. After 4 months, reobturation was revealed at the site of repair in one case, which required implantation of an additional stent coated with polytetrafluoroethylene. The patency of the biliary tract was preserved in the remaining patients in the above period.     

Birth and death of protein domains: A simple model of evolution explains power law behavior

Background  

Power distributions appear in numerous biological, physical and other contexts, which appear to be fundamentally different. In biology, power laws have been claimed to describe the distributions of the connections of enzymes and metabolites in metabolic networks, the number of interactions partners of a given protein, the number of members in paralogous families, and other quantities. In network analysis, power laws imply evolution of the network with preferential attachment, i.e. a greater likelihood of nodes being added to pre-existing hubs. Exploration of different types of evolutionary models in an attempt to determine which of them lead to power law distributions has the potential of revealing non-trivial aspects of genome evolution.