Fluctuation approach to description of nonideal plasma. I: Equilibrium plasma

A model capable of describing the kinetics of collisional recombination in nonideal plasmas by the methods of molecular dynamics is developed. The dependence of the collisional recombination rate on the coupling parameter is found to differ substantially from the extrapolation of the three-body recombination rate in nonideal plasmas. A sharp decrease in the recombination rate in strongly nonideal plasmas is revealed. As the coupling parameter decreases, collisional recombination transforms into three-body recombination.     

Determination of pair interaction potential of particles in nonideal dissipative systems

A new method is proposed for reconstructing physical characteristics of nonideal systems by solving of an inverse problem in which the motion of interacting particles is described by a set of Langevin equations. The method allows one to simultaneously determine the interaction potential between dust grains, the friction coefficients, and the external confining potential. The method was verified by solving the problem numerically in a wide range of parameters typical of laboratory dusty plasmas.     

Transport properties of nonideal systems with isotropic pair interactions between particles

Results are presented from numerical investigations of the mass transfer and pair correlation in systems of interacting grains for different types of isotropic interaction potentials. The parameters are determined that govern the transport properties of nonideal dissipative systems with a large variety of model potentials. An analytic approximation for the dust grain diffusion coefficient in strongly nonideal systems is obtained.     

Fluctuation approach to description of nonideal plasma. II: Collisional recombination in nonequilibrium plasma

A model capable of describing the kinetics of collisional recombination in nonideal plasmas by the methods of molecular dynamics is developed. The dependence of the collisional recombination rate on the coupling parameter is found to differ substantially from the extrapolation of the three-body recombination rate in nonideal plasmas. A sharp decrease in the recombination rate in strongly nonideal plasmas is revealed. As the coupling parameter decreases, collisional recombination transforms into three-body recombination.     

Molecular dynamic simulations of electric microfield distributions in a nonideal electron-positron plasma

A symmetric model of a two-component plasma is considered and the distributions of electric microfields acting on charged and neutral particles are calculated using the method of molecular dynamics at a fixed temperature of T = 30000 K and different values of the coupling parameter 0.2 ≤ Γ ≤ 1.2. Changes in these distributions with varying Γ are discussed. Special attention is paid to the behavior of the distribution tails. The behavior of these tails at a neutral point is shown to agree with the tails of the Holtsmark distribution, whereas the tails of the distribution at a charge are considerably heavier and are characterized by the exponent that varies within the range from −2.2 up to −1.8 as Γ increases.     

Features of the chemical models of a nonideal atomic plasma at high temperatures

The equation of state for a hydrogen plasma at high temperatures is considered in a physical and a chemical model. A simple expression is obtained that relates the pressure correction in chemical models to the high-temperature limit of the atom partition function. This expression ensures a correct asymptotic behavior of the equation of state in the high-temperature limit. It is explained why the familiar astrophysical model of Hummer, Mihalas, and Däppen, as applied to helioseismology, yields worse results than a physical model. A modification of the astrophysical model is proposed that makes it possible to use the nearest neighbor approximation to calculate the atom partition function in chemical models in solving astrophysical problems and problems concerning low-temperature plasmas.     

Fluorescent probe--a cholesterol analog: localization in plasma lipoproteins and in model lipid particles

The absorption spectrum of fluorescent probe--a cholesterol analog cholesta-5,7, 9(11)-trien-3 beta-ol has a vibrational structure with the maximum 326 nm. Its fluorescence spectra maximum is 370 nm. The localization of the probe in lipoproteins of high, low and very low density and in lipid spheres is studied. There are measured the areas, which occupied one molecule of cholesterol and phosphatidyl choline on the surface of lipid spheres and the radius of the lipid spheres. The localization of the probe in lipoproteins and lipid spheres is determined. The areas which occupied one molecule of phosphatidyl choline on the surface of lipid sphere is equal to the same area in mono- and bilayers. Cholesterol has the same condensing action on phosphatidyl choline in lipid spheres as in mono- and bilayers. All the probe molecules are localized on the surface of lipid spheres and lipoproteins and the B-ring of the molecule is immersed on 1.3 +/- 0.2 nm relative to polar groups. The hydroxyl group of cholesterol is arranged near the carbonyl group of phospholipid and the formation of the H-bond between these groups is possible.     

Investigation of the mechanisms for stark broadening and shift of the spectral lines in a nonideal plasma

Abstrac A method for calculating the Stark broadening and shift of the spectral lines was developed based on a combination of the ion plasma model and new theoretical and computational methods for taking the Stark effect into account. Theoretical results are compared with experimental data on the broadening and shift of the spectral lines in a strongly nonideal plasma. __________ Translated from Fizika Plazmy, Vol. 30, No. 10, 2004, pp. 944–947. Original Russian Text Copyright ? 2004 by Denisov, Orlov, Fortov, Kulish, Gryaznov, Mintsev.     

Fluorescence correlation spectroscopy and nonideal solutions

The information that may be obtained from a fluorescence correlation spectroscopic study of a nonideal solution is considered. If all of the macromolecules in a two-component solution are fluorescently labeled, the mutual diffusion coefficient will be measured. If only a few of the macromolecules in a solution are fluorescently labeled, the tracer diffusion coefficient will be obtained. Two nonideal systems that probably may usefully be studied with fluorescence correlation spectroscopy are proposed. The application of fluorescence correlation spectroscopy to studies of lateral diffusion in biological membranes is discussed; the form of the contribution to the fluorescence correlation spectrum of bulk motion within a membrane is noted.     

Formation of phospholipid-rich HDL: a model for square-packing lipoprotein particles found in interstitial fluid and in abetalipoproteinemic plasma

The major bovine HDL subfraction, fraction I-HDL, was incubated with increasing amounts of dimyristoylphosphatidylcholine (DMPC). HDL size, as determined by gradient gel electrophoresis and electron microscopy, increased with increasing HDL-phospholipid to DMPC mole ratios. Control fraction I-HDL were spherical, hexagonally-packing particles with a peak on gradient gel electrophoresis at 12.3 +/- 0.1 nm; at a ratio of 1:0.5, larger, mainly spherical particles with a peak at 12.9 +/- 0.08 nm were formed. At a ratio of 1:1, occasional square-shaped particles were seen by electron microscopy; by gradient gel analysis, the mean diameter of the HDL-product increased to 13.7 +/- 0.1 nm. At the 1:2 ratio, extensive domains of square-packing particles were noted; the major size peak of this product was 14.6 +/- 0.08 nm. In all incubations with DMPC, a small 9.4 +/- 0.08 nm product was formed; it was most pronounced at the 1:2 ratio. The large, less dense particles generated by incubation contained apolipoprotein A-I and small molecular weight proteins. The 9.4 nm product contained only apolipoprotein A-I. The less dense product formed during incubation at the 1:2 ratio had a decreased protein-to-lipid ratio relative to control HDL and a 2-fold increase in percent phospholipid. At a 1:2 ratio, incorporation of DMPC into fraction I-HDL results in the loss of one molecule of apolipoprotein A-I; the resultant particle is a stable phospholipid-rich and protein-poor HDL which has a square-packing geometry. These phospholipid-laden HDL are morphologically similar to lipoproteins isolated from interstitial fluid or from plasma of abetalipoproteinemic patients. Our data suggest that the unusual morphological properties of the latter biologically formed particles may be due to increases in the polar lipid contents, and concomitant decreases in surface protein.     

Stochastic compartmental model with branching particles

A multi-compartmental model with particles producing offspring according to the Markov branching process has been studied. Explicit results are given for the two-compartmental system and for irreversible general multicompartmental systems. The known models in stochastic compartmental analysis are shown to be particular cases of this model and applications are cited.     

Rectangular arrays of intramembranous particles on freeze-fractured chlamydomonas plasma membranes

In unfixed, freeze-fractured Chlamydomonas eugametos large numbers of rectangular ‘plaques’ are present on the plasma membrane (pm) external face (EF) in the region of the pm overlying the chloroplast. Fixation for 15 min in 1.5% glutaraldehyde (GA) cause displacement of these plaques to the complementary protoplasmic face (PF) where they occured as tightly packed arrays of intramembranous particles (IMPs). Increasing the fixation period up to 90 min produced a gradual return of array IMPs to the EF and by 24 h there was little difference in appearance between fixed and unfixed membranes. These observations indicate that plaques and rectangular arrays are different manifestations of the same basic structure. Fixation with formaldehyde (FA) failed to produce arrays on the PF but reduced the amount of material adherent to the surface of the membrane overlying arrays. Array IMPs extend to the cytoplasm and are closely packed with a centre to centre spacing of approximately 9 nm.     

Preparation of UHMWPE particles and establishment of inverted macrophage cell model to investigate wear particles induced bioactivites

Total joint replacement surgery has been widely applied to patients with severe osteoarthritis. Aseptic loosening induced by wear particles generated during joint movement is the major reason causing the failure of joint implants. Interaction of ultra-high molecular weight polyethylene (UHMWPE) wear particles with macrophages stimulates the release of inflammatory cytokines and leads to bone resorption and osteolysis. Effect of UHMWPE particle size and shape on the bioactivities remains unclear due to the lack of particles with controlled morphology as well as adequate in-vitro cell culture models for further investigations. We have developed a micro-cutting procedure to generate UHMWPE particles with desired sizes and shapes by rubbing UHMWPE with microfabricated surfaces. A narrow distribution and sterility of the generated particles was achieved. An inverted cell culturing apparatus and procedures were created and the contact between particles and macrophage cells was observed. No significant difference of the cell proliferations under normal and inverted positions further demonstrates the feasibility of the system. This newly developed platform can assist in the further understanding of the mechanism and therapy strategies of osteolysis induced by polyethylene particles.     

Radial electric field and rotation of the ensemble of plasma particles in tokamak

The velocity of macroscopic rotation of an ensemble of charged particles in a tokamak in the presence of an electric field has been calculated in a collisionless approximation. It is shown that the velocity of toroidal rotation does not reduce to a local velocity of electric drift and has opposite directions on the inner and outer sides of the torus. This result is supplemented by an analysis of the trajectories of motion of individual particles in the ensemble, which shows that the passing and trapped particles of the ensemble acquire in the electric field, on the average, different toroidal velocities. For the trapped particles, this velocity is equal to that of electric drift in the poloidal magnetic field, while the velocity of passing particles is significantly different. It is shown that, although the electric-field-induced shift of the boundaries between trapped and passing particles in the phase space depends on the particle mass and charge and is, in the general case, asymmetric, this does not lead to current generation.     

Stochastic model of localized adsorption of particles on membranes

A stochastic model of localized adsorption of particles on the membrane was constructed. In the model, the transitional processes were neglected, and adsorption was represented as a stationary Markov process. In the framework of this approach, stationary values of average numbers of particles, there dispersion, correlation function, and spectral density were estimated. It was shown that the comparison of theoretical and experimental correlation functions (or spectral density) enables one to obtain new information about the adsorption parameters, namely: formation and decomposition rate constants for a complex of an adsorbed particle with the absorption center.     

Effect of urea on the plasma membrane particles in yeast cells and protoplasts

Summary Urea in 4 to 8 M concentrations causes aggregation of the plasma membrane particles in yeast cells. Particle counting and the direction of the thread-like deformed particles indicates the translational movement of the particles along the supporting membrane. The aggregation of the particles was prevented by fixation of the cells with glutaraldehyde. Urea changed also the splitting characteristics of the membranes: faces of the plasma membrane covered with the particles were exposed less often. Yeast protoplasts were mostly desintegrated by urea solutions. In resistant protoplasts the particles were normally dispersed. Due to a strong hypertony of the urea solutions profound changes in plasma membrane invaginations were induced in yeast cells.     

Analysis of sedimentation equilibrium distributions reflecting nonideal macromolecular associations

A rigorous statistical-mechanical approach is adopted to derive general quantitative expressions that allow for the effects of thermodynamic nonideality in equilibrium measurements reflecting interaction between dissimilar macromolecular reactants. An analytical procedure based on these expressions is then formulated for obtaining global estimates of equilibrium constants and the corresponding reference thermodynamic activities of the free reactants in each of several sedimentation equilibrium experiments. The method is demonstrated by application to results from an ultracentrifugal study of an electrostatic interaction between ovalbumin and cytochrome c (Winzor, D. J., M. P. Jacobsen, and P. R. Wills. 1998. Biochemistry. 37:2226-2233). It is demonstrated that reliable estimates of relevant thermodynamic parameters are extracted from the data through statistical analysis by means of a simple nonlinear fitting procedure.