Vacancy formation in a 1D chain of dust particles in a DC discharge.

The paper presents the first experimental observation of an atypical phenomena during self-organization of dust particles into a one-dimensional chain structure levitated vertically in the plasma of a DC glow discharge. Using a laser, the third (middle) dust particle was removed from the chain of five particles so that the positions of the remaining particles did not significantly change, and a vacancy occurred in the place of the removed particle. This state of the chain turned out to be very stable, which is confirmed by the observation of the subsequent exchange of places of the fourth and the fifth particles of the chain upon the action of the laser on the forth particle. After the exchange process, vertical positions of all particles (first, second, fourth and fifth) in the chain remained almost the same as before the exchange, and the vacancy at the position of the third particle was preserved. The experimental data and the video record of the observed phenomena as well as the estimates of the plasma parameters are presented. An assumption has been made about the mechanism of the discovered phenomena that at present discharge conditions both the vacancy formation and the dust particles positions exchange are possible due to a strong ion wakes which are formed behind the upstream dust particles of the chain.

Structural properties of a chain of dust particles in a field of external forces.

This paper presents a numerical study of the structural parameters of a one-dimensional chain of three dust particles levitating in the near-electrode layer of an rf discharge or in the stratum of a dc discharge. The model considers the motion of dust particles under the action of gravity, external electric field, the Coulomb repulsion, and the electrostatic force from the space charge surrounding the dust particles. Particular attention is paid to the effect of plasma polarization around dust particles and the wake formation under the action of the external electric field. Calculations showed that the charge of the first dust particle in the chain and the total charge of the entire chain, as well as the length of the chain, grow linearly with the external electric field strength. Obtained data are in qualitative agreement with the experimental and numerical data presented in the literature. It was shown that for a certain large value of the external electric field, the charge of the third dust particle is the smallest of all the particles in the chain. It was found that with an increase in the mean value of the external electric field, the chain of dust particles is displaced as a whole in the direction opposite to the action of the electrostatic force on them.

Strain specific motility patterns and surface adhesion of virulent and probiotic Escherichia coli.

Bacterial motility provides the ability for bacterial dissemination and surface exploration, apart from a choice between surface colonisation and further motion. In this study, we characterised the movement trajectories of pathogenic and probiotic Escherichia coli strains (ATCC43890 and M17, respectively) at the landing stage (i.e., leaving the bulk and approaching the surface) and its correlation with adhesion patterns and efficiency. A poorly motile strain JM109 was used as a control. Using specially designed and manufactured microfluidic chambers, we found that the motion behaviour near surfaces drastically varied between the strains, correlating with adhesion patterns. We consider two bacterial strategies for effective surface colonisation: horizontal and vertical, based on the obtained results. The horizontal strategy demonstrated by the M17 strain is characterised by collective directed movements within the horizontal layer during a relatively long period and non-uniform adhesion patterns, suggesting co-dependence of bacteria in the course of adhesion. The vertical strategy demonstrated by the pathogenic ATCC43890 strain implies the individual movement of bacteria mainly in the vertical direction, a faster transition from bulk to near-surface swimming, and independent bacterial behaviour during adhesion, providing a uniform distribution over the surface.

Laser-induced melting of two-dimensional dusty plasma system in RF discharge.

We present a detailed analysis of experimental study, which shows clear evidence of a two-stage melting process of a quasi-two-dimensional dusty plasma system in a high-frequency gas discharge. We accurately calculated global parameters of the orientational and translational order, as well as their susceptibilities to determine two critical points, related to "solid-to-hexatic" and "hexatic-to-liquid" phase transitions. The nature of the emerging defects and changes in their mutual concentration, in addition to the estimate of core energy of free dislocations also counts in favor of the formation of an intermediate hexatic phase. These results are fully consistent with the Berezinsky-Kosterlitz-Thouless theory.

Experimental study of the nonreciprocal effective interactions between microparticles in an anisotropic plasma.

There is a variety of cases in nature when the action-reaction symmetry is broken. In particular, suitable conditions for this are realized in colloidal suspensions and complex plasmas. Since the first theories and simulations of the nonreciprocal effective interactions between microparticles in complex plasmas were published in 1995-1996, there have been hundreds of studies in the theoretical development of this theme. However, despite such a rich theoretical background, one of the important unsolved problems is a direct experimental determination of the nonreciprocal interparticle interaction forces. Here, we studied experimentally in detail the forces of the nonreciprocal effective interaction between microparticles suspended a radio-frequency produced plasma sheath. For this purpose, an experimental method based on an analysis of the spectral density of random processes in an open dissipative two-particle system was developed. In contrast to previous investigations, the proposed method takes into account random and dissipative processes in the system, does not require a special design of the experimental setup and any external perturbations, pre-measurements of external fields and any assumptions about the type of interaction. We found that even small charge changes of one particle, caused by its thermal motion in a wake field of another particle, can lead to a significant change in the effective (measurable) interaction between the particles.

Dust-acoustic soliton breaking and the associated acceleration of charged particles.

The breaking of a plane self-excited dust-acoustic soliton in a dust cloud formed in stratified dc glow discharge plasma is studied. Both macroscopic and kinetic parameters of the dust component near the soliton are experimentally obtained. It is shown that the breaking of a soliton can accelerate charged particles to supersonic speeds. The theoretical interpretation of the experimental results is performed in the framework of the hydrodynamic plasma approach, as well as the single-particle approximation. Both dissipative and nondissipative cases are considered.

Plasma anisotropy around a dust particle placed in an external electric field.

A self-consistent model of plasma polarization around an isolated micron-sized dust particle under the action of an external electric field is presented. It is shown that the quasineutral condition is fulfilled and the formed volume charge totally screens the dust particle. The ion focusing and wake formation behind the dust particle are demonstrated for different ion mean free paths and the external electric fields. It is obtained that at low values of the external electric field the trapped ions play the main role in the screening of the dust particle charge. For high external electric fields, the density of trapped ions decreases and the dust particle is screened mainly by the free ions.

[The clinical laboratory features of toxoplasmosis шт women with gynecological diseases.]

The article presents the results of clinical laboratory examination of women (n=104) with gynecological diseases for detection of Toxoplasma gondii. The antibodies to T. gondii were detected in 39.42% of women using enzyme-linked immunosorbent assay and indirect immuno-fluorescence test. In women with various gynecological diseases the toxoplasmosis is detected against the background of concomitant extra-genital pathology. This disease takes its course mostly latent together with urogenital infections being accompanied by hemostasis changes. The detection of antibodies to T. gondii in most cases of inflammation process in oviducts, uterus, ovaries can indicate the role of toxoplasma in development of inflammation diseases of female genitals.

Nonthermal plasma affects viability and morphology of Mycoplasma hominis and Acholeplasma laidlawii.

AIM: To study the effects exerted by argon microwave nonthermal plasma (NTP) on cell wall-lacking Mollicutes bacteria. METHODS AND RESULTS: 10(8) CFU ml(-1) agar plated Mycoplasma hominis and Acholeplasma laidlawii were treated with the nonthermal microwave argon plasma for 30-300 s. The maximal 10- and 100-fold drop was observed for A. laidlawii and Myc. hominis, respectively. Similarly treated Escherichia coli and Staphylococcus aureus demonstrated the 10(5) and 10(3) drop, respectively. Removal of cholesterol affected resistance of A. laidlawii. 10 mmol l(-1) antioxidant butylated hydroxytoluene decreased mortality by a factor of 25-200. UV radiation alone caused 25-85% mortality in comparison with the whole NTP. Exogenously added hydrogen peroxide H2O2 did not cause mortality. NTP treatment of Myc. hominis triggered growth of microcolonies, which were several tenfold smaller than a typical colony. CONCLUSIONS: Despite the lack of cell wall, A. laidlawii and Myc. hominis were more resistant to argon microwave NTP than other tested bacteria. Mycoplasma hominis formed microcolonies upon NTP treatment. A role of UV and active species was demonstrated. SIGNIFICANCE AND IMPACT OF THE STUDY: The first study of NTP effects on Mollicutes revealed importance of a membrane composition for bacterial resistance to NTP. New specific Myc. hominis morphological forms were observed. The study confirmed importance of the concerted action of reactive oxygen species (ROS) with UV and other plasma bioactive agents for NTP bactericidal action.

Non-thermal Plasma Causes p53-Dependent Apoptosis in Human Colon Carcinoma Cells.

Non-thermal plasma (NTP) consists of a huge amount of biologically active particles, whereas its temperature is close to ambient. This combination allows one to use NTP as a perspective tool for solving different biomedical tasks, including antitumor therapy. The treatment of tumor cells with NTP caused dose-dependent effects, such as growth arrest and apoptosis. However, while the outcome of NTP treatment has been established, the molecular mechanisms of the interaction between NTP and eukaryotic cells have not been thoroughly studied thus far. In this work, the mechanisms and the type of death of human colon carcinoma HCT 116 cells upon application of non-thermal argon plasma were studied. The effect of NTP on the major stress-activated protein p53 was investigated. The results demonstrate that the viability of HCT116 cells upon plasma treatment is dependent on the functional p53 protein. NTP treatment caused an increase in the intracellular concentration of p53 and the induction of the p53-controlled regulon. The p53-dependent accumulation of active proapoptotic caspase-3 was shown in NTP-treated cells. The study was the first to demonstrate that treatment of human colon carcinoma cells with NTP results in p53-dependent apoptosis. The results obtained contribute to our understanding of the applicability of NTP in antitumor therapy.

Coulomb clusters of dust particles in a cusp magnetic trap under microgravity conditions.

We have performed experimental and theoretical investigation of the formation and behavior of Coulomb clusters of charged diamagnetic particles in a cusp magnetic trap under microgravity conditions aboard the International Space Station. Graphite particles of 100-400 µm in size were used in experiments due to the highest specific magnetic susceptibility. We have observed the formation of clusters in the shape of an oblate ellipsoid of revolution and their oscillations after dynamical action by changing the magnetic field. Observing the excitation and damping of oscillations we have made some estimations. Molecular dynamics simulations of the observed processes have been made. Their results are in reasonable agreement with experiments. Some differences are evidently due to some unaccounted-for reasons.