Biomedical subjects

A A Lushnikov

Publications and source records attributed to A A Lushnikov.

At least 19 recordsLinked to original sources

PubMed2006

Sol-gel transition in a source-enhanced coagulating system.

This paper considers the time evolution of disperse systems in which binary coagulation and a source of fresh particles govern the temporal changes to the particle mass spectra. The source is assumed to produce fresh particles at a constant rate. The Smoluchowski equation describing the time evolution of the particle mass spectrum is solved exactly for the coagulation kernel proportional to the product of masses of two coalescing particles. It is shown that after a critical time tc a gel forms in the system and the sol spectrum becomes an algebraic function of the particle mass at t=tc. It begins to shrink after the critical time due to the mass loss supporting the growth of the gel mass. The pre- and post-critical behavior of the mass spectrum and its integral characteristics (total particle number and mass concentrations) are investigated for the source productivity I(g) dropping down algebraically with the particle mass g as I(g) proportional variant g -gamma. The critical particle mass spectrum is proved to be a universal function of (it drops down as g -5/2) if the third moment of I(g) is finite (gamma>4). Otherwise (3<gamma< or =4)this and other critical exponents begin to depend on . Still the mass spectrum remains self-similar, i.e., it depends on a combination of g and t. At smaller gamma the gelation process is shown to begin at t=0. All critical characteristics of the particle mass spectrum are determined for this case.

Journal Article↗

PubMed2006

Exact kinetics of sol-gel transition in a coagulating mixture.

The formation of a gel in a two component disperse system wherein binary coagulation governs the temporal changes to particle composition spectra is studied under the assumption that the coagulation kernel is proportional to m1n2+m2n1, with m,n being the numbers of monomers of the first and the second component in the coalescing pair of particles. This model is shown to reveal the sol-gel transition, i.e., the formation of one giant cluster with the mass comparable to the total mass of the whole system. This paper reports on the exact solution of this model within the Marcus-Lushnikov stochastic scheme. The evolution equation for the generating functional of the probability to find in the system a given set of occupation numbers (the numbers of particles containing m and n monomers of each component) at time t is formulated and solved exactly. The expression for the particle composition spectrum is derived and analyzed in the thermodynamic limit. It is shown that after a critical time a giant single particle (the gel) appears. The time evolution of its composition is found. Special attention is given to the transition point, where the gel is appearing. The time dependencies of the gel composition, the number concentration, and the second moments of the particle composition spectrum are found.

Journal Article↗

PubMed2005

Exact kinetics of the sol-gel transition.

The formation of a gel in a disperse system wherein binary coagulation alone governs the temporal changes of particle mass spectra is studied under the assumption that the coagulation kernel is proportional to the product of masses of coalescing particles. This model is known to reveal the sol-gel transition, i.e., the formation of one giant cluster with the mass comparable to the total mass of the whole system. This paper reports on the exact solution of this model for a finite total mass of the coagulating system. The evolution equation for the generating functional defining all properties of coagulating systems is solved exactly for this particular kernel. The final output is the exact expression for the single-particle mass spectrum as a function of time. The analysis of the spectrum in the thermodynamic limit shows that after a critical time a giant single particle (the gel) appears. Although the concentration of this giant gel particle is zero in the thermodynamic limit, it actively interacts with smaller particles "eating" them and thus growing in mass. Special attention is given to the transition point, where the gel is appearing. It is demonstrated that the sol-gel transition reminds the second-order phase transition. The time dependencies of the gel mass, the number concentration, and the second moment of the particle mass spectrum are found.

Journal Article↗

PubMed2004

From sol to gel exactly.

The time evolution of a disperse system wherein the binary coagulation alone governs the temporal changes of particle mass spectra is studied under the assumption that the coagulation kernel is proportional to the product of masses of the coalescing particles. This model is known to reveal the sol-gel transition, i.e., the formation of a cluster with mass comparable to the total mass of the whole system. This Letter reports on the exact solution of this model. The single-particle mass spectrum is analyzed in the thermodynamic limit and it is demonstrated explicitly how the gel appears in the system.

Journal Article↗

PubMed2004

Flux-matching theory of particle charging.

A new flux-matching theory is formulated and applied to the study of particle charging by ions. Assuming that the ion-particle interaction includes the Coulomb + polarization forces the collisionless kinetic equation is solved and the ion concentration profile in the free-molecule zone (at the distances less than the ion mean free path) is found. This profile is then matched to that derived from the solution of the diffusion equation, which describes the ion transport outside the free-molecule zone. Three matching parameters are introduced: the ion flux, the matching distance, and the ion density at the matching distance; and three conditions are formulated for fixing these parameters: (i) the constancy of the total ion flux, (ii) the continuity of the ion concentration profile, and (iii) the continuity of the derivative of the ion concentration profile. The charging efficiencies are expressed in terms of their free-molecule values, the ion diffusivity in the carrier gas, and the ion thermal velocity. This approach is applied for calculating the efficiencies of particle charging in the transition regime (the particle size is comparable to the ion mean free path and the Coulomb length). The corrections due to ion-carrier gas interaction to the particle-ion recombination rate are shown to remain finite even for very small particles, whereas in the case of particle-ion repulsion the contribution of ion-molecular collisions to the rate of particle charging is suppressed in the free-molecule regime.

Journal Article↗

PubMed2002

Singular self-preserving regimes of coagulation processes.

The late stages of the time evolution of disperse systems when either coagulation alone governs the temporal changes of particle mass spectra or simultaneous condensation complicates the evolution process are studied under the assumption that the condensation efficiencies and coagulation kernels are homogeneous functions of the particle masses, with gamma and lambda being their homogeneity exponents, respectively. In considering the asymptotic behavior of the particle mass distributions the renormalization-group approach is applied to three types of coagulating systems: free coagulating systems in which coagulation alone is responsible for disperse particle growth; source-enhanced coagulating systems, where an external spacially uniform source permanently adds fresh small particles, with the particle production being a power function of time; and coagulating-condensing systems in which a condensation process accompanies the coagulation growth of disperse particles. The particle mass distributions of the form N(A)(g,t)=A(t)psi(gB(t)) are shown to describe the asymptotic regimes of particle growth in all the three types of coagulating systems (g is the particle mass). The functions A(t) and B(t) are normally power functions of time whose power exponents are found for all possible regimes of coagulation and condensation as the functions of lambda and gamma. The equations for the universality function psi(x) are formulated. It is shown that in many cases psi(x) proportional, variant x(-sigma) (sigma > 1) at small x, i.e., the particle mass distributions are singular. The power exponent sigma is expressed in terms of lambda and gamma. Two exactly soluble models illustrate the general theoretical consideration.

Journal Article↗

PubMed2001

Nonsingular self-preserving regimes of coagulation-condensation process.

Growth of disperse particles is considered assuming that the preexisting disperse particles coagulate and grow simultaneously by condensing a low volatile substance (vapor, in what follows) whose concentration is permanently refreshed by a spatially uniform and constant in time source. The kinetics of the condensation-coagulation process is studied under the assumption that the condensation rate and coagulation kernels are homogeneous functions of the particle masses. The power exponents characterizing these functions define the asymptotic self-preserving regimes of the particle growth. Four such regimes are detected: (i) the mass of the disperse phase consumes all vapor and grows linearly with time, while the vapor concentration grows (or even drops) with time as its power s<1; (ii) the mass of the disperse phase grows slower than a linear function of time, while the vapor concentration grows asymptotically as time; (iii) the mass of disperse phase remains finite; and (iv) both, the mass of disperse phase and the vapor concentration grow linearly with time. For all above regimes the equations are derived defining the shape of the asymptotic mass distribution. The latter is shown to depend on a combination of the particle mass and time. The theory is illustrated by two exactly soluble models, and numerical results for the condensation-coagulation growth of aerosol particles in free molecular regime.

Journal Article↗

PubMed2001

Kinetics of nucleation controlled formation and condensational growth of disperse particles.

The kinetics of nucleation controlled formation and condensational growth of disperse particles is considered under the assumptions that: (i) only a small amount of condensable substance nucleates and forms the particles that grow by condensing the rest of the substance. (ii) The condensation efficiency is a power function of the particle mass. A nontrivial perturbation theory with respect to the smallness parameter mu= (the mass of nucleated matter)/(the total mass of condensable matter) is developed allowing one to describe the source-enhanced and free (no source) condensation processes in terms of universal functions: the particle-mass spectrum and the concentration of condensable matter. The theory relies upon a scaling transformation that removes at all the smallness parameter from the evolution equations (if the nucleation rate is a power function of the concentration of condensable matter) or leaves it in the expression for the nucleation rate where this parameter defines only a concentration scale of the nucleation process (for the nucleation rates of general form). The theory is illustrated by the exact analytical solutions of the nucleation-condensation kinetic equations for three practically important cases: (i) gas-to-particle conversion in the free-molecular regime, (ii) formation and diffusion controlled condensational growth of islands on surfaces, and (iii) formation and diffusion controlled growth of disperse particles in the continuum regime. The analytical expressions for the mass spectra of growing particles are found in the case of free condensing particles. The final mass spectra in free condensing systems display rather unusual behavior: they are either singular at small particle masses or not, depending on the value of the power exponent in the mass dependence of the condensation rate.

Journal Article↗

PubMed1986

The kanamycin resistance gene expression in Escherichia coli as affected by specific yeast sequences.

It was shown that the transcription initiation of the kanamycin resistance gene (the Km gene) from transposon Tn5 in E.coli HB101 strain can be provided by specific yeast sequences. To localize a region of the yeast DNA involved in transcription initiation, a number of hybrid plasmids containing promoterless part of the Km gene fused with DNA sequences from chromosome III of the yeast Saccharomyces cerevisiae was constructed. Comparison of nucleotide sequences lying in the LTR of the yeast transposon Tyl-17 with the consensus bacterial promoter revealed strong similarities.

Base Sequence↗

PubMed1986

Yeast centromeric plasmids as shuttle vectors between Escherichia coli, Bacillus subtilis and Saccharomyces cerevisiae.

A number of hybrid plasmids which can autonomously replicate in E. coli, B. subtilis and S. cerevisiae was constructed. Replication of these plasmids both in yeast and in B. subtilis starts on a sequences originating from Staphylococcus aureus plasmids pC194 and pE194. In yeast these hybrids are unstable like those yeast vectors which contain eukaryotic ARSs, but their stability has been increased by addition of yeast centromeric sequence. Both pC194 and pE194 DNAs contain sequences which reveal strong similarities with the yeast ARS consensus. Nevertheless the replication efficiences of these plasmids in yeast are different.

Bacillus subtilis↗

PubMed1985

Bacterial vectors which confer resistance to kanamycin.

On the base of plasmid pLD720 (a deletion derivative of the cosmid vector pHC79) a number of hybrid plasmids which confer in Escherichia coli cells the kanamycin resistance was constructed. All hybrid plasmids contain the promoterless part of kanamycin resistance gene (which codes for aminoglycoside 3'-phosphotransferase II) from transposon Tn5. The Km gene expression is driven by a promoters situated on pLD720. The hybrid plasmids pLD723, pLD724 and pLD728 contain a complete DNA sequences of plasmids pC194 or pE194 from Staphylococcus aureus that permits them to replicate into Bacillus subtilis as well. However, no expression of the Km gene in Bacillus subtilis was observed. There is a unical Bgl II site on pLD728 is front of the beginning of a Km gene structural part. This property of pLD728 may be useful when cloning in this plasmid a promoter sequences of different species.

Bacillus subtilis↗

PubMed1985

Shuttle vector for Escherichia coli, Pseudomonas putida, and Pseudomonas aeruginosa.

A hybrid plasmid capable of replication in 2 different genera, Escherichia and Pseudomonas, was constructed. This plasmid DNA can be used as a cloning vector in E. coli and pseudomonades cells. The described hybrid plasmid pLD411 has been constructed on the basis of 2 small E. coli vector R-plasmids used in our laboratory and cryptic plasmid pWW2 or P. putida MT1. Plasmid pLD411 DNA was mapped with restrictases; its biological activity in transformations of different bacterial strains was studied, and the characteristics of transformed cells were also described.

Cloning, Molecular↗

PubMed1982

[Molecular size of plasmid R18 and its substituted variants in Escherichia coli cells].

R-substituted plasmids (R18Arg) obtained from plasmid R18 and capable to convert Arg- strains E coli to Arg+ strains at the expense of genetic material mobilized from P. aeruginosa chromosome are physically unstable and exist as molecules of different size. It was shown that the physical size of plasmid R18Arg is 3--5 megadaltons greater than those of plasmid R18.

Crosses, Genetic↗

PubMed1977

[Heterologous transformation in Bacillus subtilis. 1. Transmission of DNA of the R1drd19 plasmid].

Bac. subtilis 168 (BD-25) cells were infected with DNA of plasmide R1drd19 isolated from E. coli strain; transformants resistant to streptomycin (500 microgram/ml) and kanamycin (40 microgram/ml) appeared with the frequency of 2.10(-6). These transformants retained resistance to the mentioned antibiotics stably. A satellite DNA peak was revealed in centrifugation in the density gradient of cesium chloride with ethidium bromide. It was possible to infect cells of Bac. subtilis 168 (BD-25) with plasmide DNA isolated from the transformants. Plasmide transduction with the aid of phages AR9 and PBSI multiplied on the transformant strains was also effected. Physico-chemical analysis of the transformed plasmide DNA was conducted; its molecular weight was determined.

Bacillus subtilis↗

PubMed1973