Fundamental groups of asymptotic cones

We show that for any metric space $M$ satisfying certain natural conditions, there is a finitely generated group $G$, an ultrafilter $\omega$, and an isometric embedding $\iota$ of $M$ to the asymptotic cone ${\rm Cone}_\omega (G)$ such that the induced homomorphism $\iota ^ \ast :\pi_1(M)\to \pi_1({\rm Cone}_\omega (G))$ is injective. In particular, we prove that any countable group can be embedded into a fundamental group of an asymptotic cone of a finitely generated group.Comment: This is a corrected version of the paper. Some proofs are improved and several typos are corrected. The main result remains unchange

Evolutionarity of MHD shock waves in collisionless plasma with heat fluxes

The evolutionarity conditions for the MHD shock waves are considered within the framework of the 8-moment approximation for collisionless plasma with heat fluxes. In the general case, evolutionarity diagrams are obtained depending on the relative magnitude of the Alfven wave velocity in front of or behind the shock wave front. The evolutionarity conditions for parallel shock waves are analyzed using previously obtained solutions for parallel MHD shock waves in collisionless plasma with heat fluxes. On the plane of dimensionless parameters characterizing plasma velocity and heat flux in front of the shock wave, the regions of evolutionarity are determined for the fast and slow shock waves propagating along the magnetic field.Comment: 22 pages, 11 figure

Peripheral fillings of relatively hyperbolic groups

A group theoretic version of Dehn surgery is studied. Starting with an arbitrary relatively hyperbolic group $G$ we define a peripheral filling procedure, which produces quotients of $G$ by imitating the effect of the Dehn filling of a complete finite volume hyperbolic 3--manifold $M$ on the fundamental group $\pi_1(M)$. The main result of the paper is an algebraic counterpart of Thurston's hyperbolic Dehn surgery theorem. We also show that peripheral subgroups of $G$ 'almost' have the Congruence Extension Property and the group $G$ is approximated (in an algebraic sense) by its quotients obtained by peripheral fillings. Various applications of these results are discussed.Comment: The difference with the previous version is that Proposition 3.2 is proved for quasi--geodesics instead of geodesics. This allows to simplify the exposition in the last section. To appear in Invent. Mat

Mechanisms of Damaging Bacteria during Lyophilization and Protective Activity of Shielding Media

Considered are the current views on the mechanisms and factors of bacterial cell degradation during lyophilization and storage of dry preparations. Given are the data on the most effective lyo-rotectors and mechanisms of their shielding action. Lyophilization or sublimation from the frozen state is the basic method of bacteria preservation in culture collections and biological resource centers. In the process of lyophilization cells are exposed to damaging stress factors. Low temperatures, water crystallization, osmotic process, pH alterations, and dehydration affect cell cultures and molecules. Oxidative reactions, running in dry cell preparations, change the composition and structure of lipids, proteins, nucleic acids, and, thereby reduce the number of living cells during the storage. One of the key factors that influences bacterial viability after lyophilization and storage is the composition of shielding medium, with which the cells are mixed up before conservation. Utilization of protective media, containing carbohydrates, amino acids, restored milk, gelatin and other components, decreases the probability of cell elements damaging and extends the assured storage life

AUTHENTICATION OF REFERENCE STRAINS OF PATHOGENIC MICROORGANISMS APPLYING AUTOMATED MICROBIOLOGICAL ANALYZER “VITEK 2”

Objective of the study was to carry out identification of reference strains of pathogenic microorganisms from stores of the State Collection of Pathogenic Bacteria (SCPB) at RusRAPI “Microbe”, using microbiological analyzer Vitek 2, followed by determination of their biochemical authenticity markers.Materials and methods. Methodological approach was based on application of automated system Vitek 2 Bio-Mérieux with the subsequent assessment of the results obtained, using BioNumerics 7.5 software package.Results and conclusions. Verified was authenticity of 103 reference strains of pathogenic microorganisms stored in SCPB, RusRAPI “Microbe”. It was established that 7 out of 103 strains (6.8 %) did not conform to the claimed feature profiles and cannot be used in scientific-practical activities, in consequence of which they were replaced with reliable authentic analogues. Evaluation of the data on interaction between the tested strains and differentiating substrates allowed for determination of authenticity markers for each of them, necessary for control of collection culture identity under reproduction and storage. On the basis of the data gathered, the profiles of the studied reference strains were regenerated

Principles of Formation of Collection Funds of Microorganism Strains

The aim of the review was to consider the principles and criteria for the formation of funds of service microbiological collections and the specialized State collection of pathogenic bacteria (SCPB) at the RusRAPI “Microbe”. The rapid pace of characterization, study, and use of microbial diversity makes the development of criteria for the selection of microorganisms for permanent storage in collections particularly relevant. The number and format of these criteria are determined by the tasks the collection centers of different levels and specialization are facing. Service collections form their funds by depositing or acquiring type, reference, educational strains. In recent years, the practicability of expanding the range of strains, the deposition of which is desirable in service collections, has been recognized. These are strains characterized by phylogenetic, genomic, metabolic, ecological uniqueness; with a fully sequenced genome; known and emerging plant, animal and human pathogens that caused disease outbreaks; used in international research projects; having biotechnological and economic significance. The main task of the SCPB as a specialized state collection of pathogenic bacteria of groups I–II is to preserve strains characterizing the intraspecific diversity and populations of pathogens circulating in natural foci or in certain territories of the Russian Federation, isolated during epizootics, local or epidemic outbreaks. The selection criteria for strains for permanent storage are their ecological, phenotypic, and genetic peculiarities. The preservation of such a collection is important for future research using new technologies and tracking the evolution of pathogenic bacteria – causative agents of particularly dangerous infectious diseases