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.     

Plasma electronics and plasma acceleration of charged particles

Preliminary results are summarized from studies on plasma electronics and plasma acceleration of charged particles, recent advances in this field are analyzed, and the challenging problems are outlined.     

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.     

The affinity of the FimH fimbrial adhesin is receptor-driven and quasi-independent of Escherichia coli pathotypes

Type-1 fimbriae are important virulence factors for the establishment of Escherichia coli urinary tract infections. Bacterial adhesion to the high-mannosylated uroplakin Ia glycoprotein receptors of bladder epithelium is mediated by the FimH adhesin. Previous studies have attributed differences in mannose-sensitive adhesion phenotypes between faecal and uropathogenic E. coli to sequence variation in the FimH receptor-binding domain. We find that FimH variants from uropathogenic, faecal and enterohaemorrhagic isolates express the same specificities and affinities for high-mannose structures. The only exceptions are FimHs from O157 strains that carry a mutation (Asn135Lys) in the mannose-binding pocket that abolishes all binding. A high-mannose microarray shows that all substructures are bound by FimH and that the largest oligomannose is not necessarily the best binder. Affinity measurements demonstrate a strong preference towards oligomannosides exposing Manalpha1-3Man at their non-reducing end. Binding is further enhanced by the beta1-4-linkage to GlcNAc, where binding is 100-fold better than that of alpha-d-mannose. Manalpha1-3Manbeta1-4GlcNAc, a major oligosaccharide present in the urine of alpha-mannosidosis patients, thus constitutes a well-defined FimH epitope. Differences in affinities for high-mannose structures are at least 10-fold larger than differences in numbers of adherent bacteria between faecal and uropathogenic strains. Our results imply that the carbohydrate expression profile of targeted host tissues and of natural inhibitors in urine, such as Tamm-Horsfall protein, are stronger determinants of adhesion than FimH variation.     

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.     

Analysis of lipid transfer activity between model nascent HDL particles and plasma lipoproteins: implications for current concepts of nascent HDL maturation and genesis

The specifics of nascent HDL remodeling within the plasma compartment remain poorly understood. We developed an in vitro assay to monitor the lipid transfer between model nascent HDL (LpA-I) and plasma lipoproteins. Incubation of α-¹²⁵I-LpA-I with plasma resulted in association of LpA-I with existing plasma HDL, whereas incubation with TD plasma or LDL resulted in conversion of α-¹²⁵I-LpA-I to preβ-HDL. To further investigate the dynamics of lipid transfer, nascent LpA-I were labeled with cell-derived [³H]cholesterol (UC) or [³H]phosphatidylcholine (PC) and incubated with plasma at 37°C. The majority of UC and PC were rapidly transferred to apolipoprotein B (apoB). Subsequently, UC was redistributed to HDL for esterification before being returned to apoB. The presence of a phospholipid transfer protein (PLTP) stimulator or purified PLTP promoted PC transfer to apoB. Conversely, PC transfer was abolished in plasma from PLTP^−/− mice. Injection of ¹²⁵I-LpA-I into rabbits resulted in a rapid size redistribution of ¹²⁵I-LpA-I. The majority of [³H]UC from labeled r(HDL) was esterified in vivo within HDL, whereas a minority was found in LDL. These data suggest that apoB plays a major role in nascent HDL remodeling by accepting their lipids and donating UC to the LCAT reaction. The finding that nascent particles were depleted of their lipids and remodeled in the presence of plasma lipoproteins raises questions about their stability and subsequent interaction with LCAT.