Biomedical subjects

D Samsonov

Publications and source records attributed to D Samsonov.

11 recordsLinked to original sources

PubMed2003

Kinetic measurements of shock wave propagation in a three-dimensional complex (dusty) plasma.

"Complex plasmas" consist of electrons, ions, and charged microparticles. The latter are individually observable, allowing kinetic measurements in plasmas. Using a sudden gas pulse, a traveling perturbation was initiated in such a complex plasma and its propagation, acceleration, and steepening-possibly into a shock was followed. The experiment was performed in the PKE-Nefedov laboratory under microgravity conditions on the international space station, i.e., in a complex plasma cloud with very little stored (potential or free) energy and thus free of, e.g., parametric instabilities. The perturbation front remained remarkably smooth, with a microroughness of the order of the interparticle distance. The observations are presented and interpreted.

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PubMed2002

Anisotropic plasma crystal solitons.

An analytical two-dimensional model for weakly dispersive and weakly nonlinear longitudinal and transverse shear waves propagating in an ideal two-dimensional hexagonal Yukawa crystal is presented. The model takes into account the nonlinear terms up to the third order. Both compressional and shear soliton solutions are found in the long-wavelength approximation. It is shown that the compressional solitons are always supersonic and weakly anisotropic. The shear solitons, on the other hand, exhibit strong anisotropy and can be both subsonic and supersonic, depending on the direction of propagation. In the model, shear solitons cannot propagate along the main axes. The role of weak damping as well as formation of multiple solitons is analyzed. The results are discussed in connection with wave and Mach cone experiments in a monolayer hexagonal plasma crystal, and a diagnostic method is proposed to measure both the charge of the microparticles and the lattice parameter.

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PubMed2002

Dissipative longitudinal solitons in a two-dimensional strongly coupled complex (dusty) plasma.

Solitary waves are experimentally studied in a monolayer hexagonal dust lattice which is formed from monodisperse plastic microspheres and levitated in the sheath of an rf discharge. It is found that the product of the soliton amplitude and the square of the soliton width is constant as the soliton propagates. The analytical theory describing the experiment is based on the equations of motion written for a linear chain. It takes into account damping, dispersion, and nonlinearity. The numerical simulation of a linear chain produces double solitons like those observed in the experiment.

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PubMed2001

Long-range attractive and repulsive forces in a two-dimensional complex (dusty) plasma.

An interaction of a negatively biased wire with a monolayer lattice of negatively charged particles has been studied experimentally. The particles levitated at the height of the wire in a sheath of an rf discharge. It was found that the particles close to the wire were repelled from it electrostatically, while the far particles were attracted due to the drag of the ion flow deflected toward the wire. The ion drag force prevails far from the wire, whereas the electrostatic force is stronger close to the wire. The range of the forces is one to two orders of magnitude greater than the screening length.

Journal Article↗

PubMed2001

Pregnancy rate and embryo loss in the NK1.1+ T cell-depleted mouse.

OBJECTIVE: To determine the role of natural killer cell (NK) 1.1+ T cells in pregnancy and in embryo loss. STUDY DESIGN: Four groups of C57 mice, consisting of 20 animals each, were studied. Groups A and B included pregnant females treated with anti-NK1.1 monoclonal antibodies until they gave birth or non-NK1.1-depleted antibodies, respectively. In order to evaluate the role of NK1.1+ T cells in pregnancy, female mice in group C were treated with anti-NK1.1 monoclonal antibodies every seven days starting seven days prior to mating until they gave birth. Control mice in group D were not NK1.1-depleted. NK1.1+ T cell depletion was determined by flow cytometric analysis. RESULTS: Depletion of NK1.1+ T cells did not significantly change the pregnancy rate, nor did it significantly alter the number of live births. Numbers of live births tended to decrease in NK1.1-depleted mice, with a mean number of live births of 4.66 as compared with 6.09 in NK1.1-depleted and nondepleted mice, respectively. Similarly, mice treated with anti-NK1.1 monoclonal antibodies every seven days starting seven days prior to mating became pregnant at a rate of 40% as compared with 60% in non-NK1.1-depleted controls. A comparable trend was observed in the number of live births, with a mean number of live births of 5.0 as compared with 6.1 in NK1.1-depleted and non-NK1.1-depleted mice, respectively. CONCLUSION: In the NK1.1-depleted mouse model, NK1.1+ T cells do not have any direct effect on pregnancy rate or on early embryo loss.

Animals↗

PubMed2000

Transverse waves in a two-dimensional screened-coulomb crystal (Dusty plasma)

Transverse shear waves were observed experimentally in a two-dimensional screened Coulomb crystal. They were excited by applying a chopped laser beam to a 2D dusty plasma, i.e., a monolayer of charged microspheres levitated in a plasma. Measurements of the dispersion relation reveal an acoustic, i.e., nondispersive, character over the entire range of wave numbers measured, 0.2<k(r)a/pi<0.7, where a is the interparticle spacing. Comparison to theory provides a measurement of the particles' charge.

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PubMed2000

Enhancement of immune tolerance via induction of NK1.1 positive liver-associated-lymphocytes under immunosuppressive conditions.

BACKGROUND/AIMS: The liver was previously shown to play a critical role in oral tolerance induction. A subset of liver-associated-lymphocytes expressing NK1.1 marker (NK1.1+ LAL) have killing activities and it has been suggested that they play a role in immune modulation. FK506 is a powerful immunosuppressive agent affecting T-cell differentiation and function. The exact pathway involved in peripheral tolerance induction using this drug remains unknown. The aim of the present study was to determine the interaction between FK506 and NK1.1+ LAL in induction of peripheral immune tolerance in the experimental colitis model. METHODS: Colitis was induced in C57 mice by intracolonic instillation of trinitrobenzenesulfonic acid (TNBS). Mice received five oral doses of colonic proteins extracted from TNBS-colitis colonic wall with and without FK506 treatment. The effect of FK506 treatment on NK1.1+ LAL was tested by cell-sorting and cytotoxicity assay. Colitis was assessed by standard clinical, macroscopic and histologic scores. RESULTS: Both FK506 treatment and oral tolerance induced a significant increase in NK1.1+ LAL number and cytotoxicity function. FK506 treatment enhanced the effect of oral tolerance on amelioration of disease activity. Orally tolerized mice treated with FK506 had no mortality nor increase in body weight, and manifested significant improvement in disease macroscopic and microscopic scores. CONCLUSIONS: This study shows for the first time that immune tolerance induced by both oral administration of an antigen and by FK506 treatment may be mediated via enhancement of NK1.1+ LAL. This subset of lymphocytes may play an immunoregulatory role in immune tolerance induction.

Animals↗

PubMed2000

Rigid and differential plasma crystal rotation induced by magnetic fields

Observations show that plasma crystals, suspended in the sheath of a radio-frequency discharge, rotate under the influence of a vertical magnetic field. Depending on the discharge conditions, two different cases are observed: a rigid-body rotation (all the particles move with a constant angular velocity) and sheared rotation (the angular velocity of particles has a radial distribution). When the discharge voltage is increased sufficiently, the particles may even reverse their direction of motion. A simple analytical model is used to explain qualitatively the mechanism of the observed particle motion and its dependence on the confining potential and discharge conditions. The model takes into account electrostatic, ion drag, neutral drag, and effective interparticle interaction forces. For the special case of rigid-body rotation, the confining potential is reconstructed. Using data for the radial dependence of particle rotation velocity, the shear stresses are estimated. The critical shear stress at which shear-induced melting occurs is used to roughly estimate the shear elastic modulus of the plasma crystal. The latter is also used to estimate the viscosity contribution due to elasticity in the plasma liquid. Further development is suggested in order to quantitatively implement these ideas.

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PubMed2000

Mach cone shocks in a two-dimensional Yukawa solid using a complex plasma

Mach cones were studied experimentally in a two-dimensional Yukawa solid consisting of charged micrometer particles suspended as a layer in a plasma. These cones were V-shaped shocks produced spontaneously by a supersonic particle moving below the main two-dimensional particle layer. The cones had a double structure. The first cone was compressional and particles moved forward, and it was followed by a second cone, which was rarefactional, where particles moved backward. Over the limited range of speed V attained by the supersonic particles in this experiment, the angle mu of the cone was found to obey the Mach cone rule sin mu = c/V, where c is the medium's sound speed. The cones caused only elastic deformations in the crystal lattice, except in a narrow track behind the cone's vertex. The wings of the cones can be analyzed as linear shocks in two dimensions. Using spatially resolved measurements of the particle number density and velocity and applying the Hugoniot relations for shocks in two dimensions, we found that the pressure inside the first Mach cone was greater than in the undisturbed medium by a factor of 1.3-1.6. The cone angle was also used to measure the charge in this experiment.

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PubMed2000

Laser-excited mach cones in a dusty plasma crystal

Experimental studies of the formation and structure of Mach cones in a plasma crystal are presented. Plasma crystals are ordered structures of charged microspheres trapped in the sheath of an rf discharge plasma. Using a monolayer crystal with a hexagonal lattice, Mach cones were excited by the radiation pressure of a focused laser beam. The beam was swept at a supersonic speed through the crystal, in a controlled and repeatable manner. A multiple Mach cone structure was observed, with at least three distinct Mach cones. The Mach angle relation was verified over a wide range of Mach numbers, for both the first and second cones. The sound speed, measured from the first Mach angle, was found to increase with the particle number density. Two methods of determining the particle charge and screening distance are developed, making use of the sound speed and an assumption of a Yukawa interparticle potential. Molecular-dynamics simulations of the experiment were carried out, using a monolayer of particles interacting through a Yukawa potential, and these show close agreement with the experiment.

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PubMed1999

Liver-associated lymphocytes expressing NK1.1 are essential for oral immune tolerance induction in a murine model.

Oral tolerance is the induction of immunological hyporesponsiveness towards orally administered antigens. Tolerance initiation involves induction of anti-inflammatory (Th2) lymphocytes, with downregulation of pro-inflammatory (Th1) lymphocytes. The liver was previously shown to play a critical role in oral tolerance induction. The aim of the present study was to test whether liver-associated-lymphocytes expressing the NK1.1 marker (NK1.1+ LAL) are substantial for induction of oral tolerance in an experimental colitis model. Colitis was induced in C57 mice by intracolonic instillation of trinitrobenzensulfonic acid (TNBS). Mice received five oral doses of colonic proteins extracted from TNBS-colitis colonic wall. Anti-NK1.1 monoclonal antibodies were injected before tolerance induction. Colitis was assessed by standard clinical, macroscopic, and microscopic scores. Serum IFN-gamma, TGF-beta1, and IL4 levels were measured by enzyme-linked immunosorbent assay. To evaluate the role of NK1.1+ LAL in keeping the balance between immunogenic and tolerogenic subsets of cells, we tested whether peripheral lymphocytes harvested from tolerized and NK1.1-depleted nontolerized mice can adoptively transfer the tolerance into naive irradiated rats. Depletion of NK1.1+ LAL prevented immune tolerance induction in the experimental colitis model. NK1.1+ LAL-depleted nontolerized mice, disclosed severe clinical, macroscopic, and microscopic parameters of colitis. These mice had significantly lower TGF-beta1, IL4, and higher IFN-gamma serum levels, and their lymphocytes failed to transfer the tolerance into naive animals. In contrast, the feeding of colitis-extracted proteins, without NK1.1+ LAL depletion, markedly alleviated the disease. Tolerized mice had higher IL4 and TGF-beta1 and lower IFN-gamma serum levels, and adoptive transfer of their suppressor splenocytes markedly alleviated colitis in naive recipients. NK1.1+ LAL plays a critical role in oral tolerance induction. Depletion of this subset of LAL prevents a shift from Th1 to a Th2 type of immune response, hindering the ability to induce immune tolerance.

Administration, Oral↗