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

Electrochemical synthesis of metal nanoparticles using a polymeric mediator, whose reduced form is adsorbed (deposited) on an electrode

© 2018, Springer Science+Business Media, LLC, part of Springer Nature. Efficient mediated electrosynthesis of nanocomposite Au@р(MVCA8+-co-St) (~6 nm), in which ultrasmall Au nanoparticles (Au-NP) were bound in nanocapsules of water-soluble nanoparticles of соpolymer р(MVCA8+-co-St) of tetraviologen calix[4]resorcinol (MVCA8+) with styrene (St), was accomplished by the reduction of AuI in aqueous medium. The quanti- tative reduction of AuI was carried out using the theoretically necessary amount of electricity and was not accompanied by the deposition of metal on the electrode. Radical cations of viologen units MV•+ of the molecule р(MVCA4•+-co-St) adsorbed on the electrode and π-dimers MV•+MV•+ of π-polymers [р(MVCA4•+-co-St)]n deposited on the electrode act- ed as the reducing agents with respect to AuI. During electrolysis, the nanoparticles agglo- merated to 37—50 nm. The nanocomposite particles dispersed in ethanol had sizes of 72±16 nm and also contained Au-NP with sizes of 51±8 and 19±3 nm. The catalytic activity of the nanocomposite in the reduction of p-nitrophenol with sodium borohydride was demon- strated. A similar reduction of AgCl nanoparticles (~250 nm) led to the formation of silver nanoparticles with crystallite sizes in the range of 7—11 nm, the process was inefficient, however, even when using 250% of electricity, an incomplete reduction of AgCl was still observed