Place In Plasma Research Articles

Axial Structure of Gas Discharge Sustained by the Eigen Dipolar Wave of The Metal Waveguide with Varying Radius Filled by Magnetized Nonuniform Plasma

The article presents the results of the theoretical study of the plasma density axial distribution in a stationary gas discharge sustained by the eigen dipolar wave that propagates in a long cylindrical plasma-metal structure. The discharge structure consists of a column of magnetized non-uniform plasma placed in the metal waveguide of variable radius. The study of the gas discharge is carried out within the framework of the electrodynamic model, in which the main attention is paid to the electrodynamic part of the model. To describe the processes that take place in plasma, the model equations are used. The influence of the metal waveguide inhomogeneity along the structure and the plasma density radial non-uniformity on the phase characteristics of the dipolar wave, its spatial attenuation, the field components radial distribution, the axial distribution of the plasma density sustained by this mode are determined. It is also analysed the condition for the discharge stability and find the regions, where dipolar mode can sustain the stable discharge. The obtained results can be useful for various technological applications.

Oxygen and magnesium mass-independent isotopic fractionation induced by chemical reactions in plasma

Enrichment or depletion ranging from -40 to +100% in the major isotopes 16O and 24Mg were observed experimentally in solids condensed from carbonaceous plasma composed of CO2/MgCl2/Pentanol or N2O/Pentanol for O and MgCl2/Pentanol for Mg. In NanoSims imaging, isotope effects appear as micrometer-size hotspots embedded in a carbonaceous matrix showing no isotope fractionation. For Mg, these hotspots are localized in carbonaceous grains, which show positive and negative isotopic effects so that the whole grain has a standard isotope composition. For O, no specific structure was observed at hotspot locations. These results suggest that MIF (mass-independent fractionation) effects can be induced by chemical reactions taking place in plasma. The close agreement between the slopes of the linear correlations observed between δ25Mg versus δ26Mg and between δ17O versus δ18O and the slopes calculated using the empirical MIF factor η discovered in ozone [M. H. Thiemens, J. E. Heidenreich, III. Science 219, 1073-1075; C. Janssen, J. Guenther, K. Mauersberger, D. Krankowsky. Phys. Chem. Chem. Phys 3, 4718-4721] attests to the ubiquity of this process. Although the chemical reactants used in the present experiments cannot be directly transposed to the protosolar nebula, a similar MIF mechanism is proposed for oxygen isotopes: at high temperature, at the surface of grains, a mass-independent isotope exchange could have taken place between condensing oxides and oxygen atoms originated form the dissociation of CO or H2O gas.

Do Redox Balance and Inflammatory Events Take Place in Mild Bronchiectasis? A Hint to Clinical Implications.

We hypothesized that in mild bronchiectasis patients, increased systemic inflammation and redox imbalance may take place and correlate with clinical parameters. In plasma samples from patients with very mild bronchiectasis, inflammatory cells and molecules and redox balance parameters were analyzed. In the patients, lung function and exercise capacity, nutritional status, bacterial colonization, and radiological extension were assessed. Correlations between biological and clinical variables were determined. Compared to healthy controls, levels of acute phase reactants, neutrophils, IgG, IgA, myeloperoxidase, protein oxidation, and GSH increased and lung function and exercise capacity were mildly reduced. GSH levels were even greater in ex-smoker and Pseudomona-colonized patients. Furthermore, radiological extension inversely correlated with airway obstruction and, disease severity, and positively correlated with neutrophil numbers in mild bronchiectasis patients with no nutritional abnormalities. In stable patients with mild bronchiectasis, several important inflammatory and oxidative stress events take place in plasma. These findings suggest that the extension of bronchiectasis probably plays a role in the development of redox imbalance and systemic inflammation in patients with mild bronchiectasis. These results have therapeutic implications in the management of bronchiectasis patients.

Development of Zeff diagnostic system on the Globus-M (M2) tokamak and the first experimental results

Studying the behavior of effective ion charge Zeff, which indicates the degree of pollution of plasma and can provide valuable information about many processes taking place in plasma, mechanisms of the releasing impurities, transport, etc is of great interest. This paper describes the development of the Zeff diagnostic system for the Globus-M2 tokamak. The effective ion charge is determined on the basis of measurements of the bremsstrahlung intensity and Thomson scattering data—Te and ne profiles. The results of the first Zeff measurements obtained for several discharges on the Globus-M tokamak are presented in this paper. The results have been validated by simulation using the ASTRA transport code for the same discharges, and it has demonstrated a good agreement with the experimental results.

Optical Emission Spectroscopy of Magnethron Discharge Ar/Cu Plasma

Plasma parameters (excitation temperature and electron density) of pulsing magnetron discharge is studied by optical emission spectroscopy. Such discharges are usually used as effective sources in sputtering or deposition processes. Vapor admixtures in argon plasma define mainly the temperature and electron density in such discharges. This is the feature, which is typically takes place in plasma of discharge between contacts/electrodes in switching devices of electric technology circuits.

Low-Frequency Kinetic Waves in Plasmas of Magnetic Loops at the Early Stage of a Flare Process in an Active Region

The process of the rise and development of low-frequency instability of kinetic Alfven waves (KAW) and kinetic ion-acoustic waves (KIAW) in preflare solar plasma near the footpoints of magnetic loops, i.e., in the area that corresponds to the height of low-middle chromosphere, has been studied. The observational data obtained in the framework of international missions Hinode, SDO, and IRIS demonstrate that a magnetic field’s amplitude can vary in the interval from a few dozen up to few hundred gausses. The existence of large-scale weak electric fields (“sub-Dreicer” in generally accepted terminology) during a long enough time (with respect to the time of instability development) can be considered in the framework of the used concept as the main source of the wave generation. One more source of instability is slow drift motions of plasma, which are the result of spatial inhomogeneties of temperature and density of a medium. Our former investigations of the obtained solutions of dispersive relation for low-frequency kinetic waves, which are generated due to the development of correspond instabilities, have established an important fact: for some semiempirical models of the solar atmosphere, the kinetic waves generated during the linear stage of the development are members of the family of kinetic Alfven waves and the family of kinetic ion-acoustic waves. It has been proven that the considered wave generation can take place in plasma with pure Coulomb conductivity as well as in plasma with saturated, small-scale Bernstein turbulence. The latter can appear in the investigated area as result of natural evolution of instability of the first harmonics of quasi-Bernstein modes. This mode has much lower threshold with respect to the amplitude of a sub-Dreicer field than low-frequency kinetic waves. Besides this fact, the waves considered have a low enough degree of plasma nonisothermality, which is needed for the appearance of instability. The principal possibility for excitation of nondamped kinetic waves with small amplitudes in the area under investigation has also been proven. It is very important for the increase in the probability for realization of the process of three-wave interaction and appearance of the spikes of microwave emission in the preflare state of the active region and, correspondingly, for making the combined short-term prediction of a flare in it.

Particle acceleration by beating of two intense cross-focused cosh-Gaussian laser beams in plasma

AbstractThe effect of two intense cross-focused cosh-Gaussian laser (CGL) beams on the generation of electron plasma wave (EPW) and particle acceleration in collisionless plasma has been investigated under the relativistic–ponderomotive regime. Due to mutual interaction of two laser beams, cross-focusing takes place in plasma. The EPW is generated by the beating of two cross-focused CGL beams of frequencies ω1 and ω2. An analytical expression for the beamwidth of laser beams and EPW as well as the power of the generated EPW has been evaluated using Wentzel–Kramers–Brillouin and paraxial approximations. The energy of the accelerated electrons by the beat-wave process has also been calculated. Numerical simulations have been carried out to investigate the effect of typical laser plasma parameters on the power of excited EPW and acceleration of electrons. The results are compared with only relativistic nonlinearity and the Gaussian profile of laser beams. It is observed that CGL beams focused earlier than Gaussian beams, which significantly affected the dynamics of plasma wave excitation and particle acceleration. Numerical results indicate that there is a remarkable change in the power of generated EPW and electron acceleration in the relativistic–ponderomotive case in comparison with only relativistic case.

Contribution of Linker Stability to the Activities of Anticancer Immunoconjugates

The linker component of antibody-drug conjugates (ADC) is a key feature in developing optimized therapeutic agents that are highly active at well tolerated doses. For maximal intratumoral drug delivery, linkers are required that are highly stable in the systemic circulation, yet allow for efficient drug release at the target site. In this respect, amide bond-based technologies constitute a technological advancement, since the linker half-lives in circulation ( t 1/2 approximately 7 days) are much longer than earlier generation linkers that break down within 1-2 days. The amide linkers, some of which contain peptides, are appended to the mAb carriers through thioether/maleimide adducts. Here, we describe that use of a bromoacetamidecaproyl (bac) in place of the maleimidocaproyl (mc) increases the plasma stability of resulting thioether ADCs. One such ADC, 1F6-C4v2-bac-MMAF, which is directed against the CD70 antigen on lymphomas and renal cell carcinoma, was prepared containing a bac thioether spacer between the drug (MMAF) and the mAb carrier (1F6-C4v2). There was no measurable systemic drug release from this ADC for 2 weeks postadministration in mice. In order to assess the impact of improving linker stability beyond mc containing ADCs, a series of mc and bac-linked 1F6-MMAF conjugates were compared for tolerability, intratumoral drug delivery, and therapeutic efficacy in nude mice with renal cell carcinoma xenografts. There were no statistically significant efficacy differences between sets of mc and bac containing ADCs, although the bac linker technology led to 25% higher intratumoral drug exposure over a 7 day period compared to the corresponding mc linker. The mechanism of drug release from maleimide-adducts likely involves a retro-Michael reaction that takes place in plasma, based on in vitro studies demonstrating that some of the released drug-maleimide derivative became covalently bound to cysteine-34 of serum albumin. In summary, the data indicate that new linkers can be obtained with improved in vivo stability by replacing the maleimide with an acetamide, but the resulting ADCs had similar tolerability and activity profiles.

Computational study of plasma-solid interaction in DC glow discharge in argon plasma at medium pressures

In the presented contribution two groups of techniques of computational physics-fluid modelling and non self-consistent particle technique were used to study plasma-solid interaction in argon plasma. We focused both on the physical processes taking place in the sheath at various pressures and on the problems of computational physics. The attention was given to preparation of two-dimensional fluid models with realistic assumptions about physical processes taking place in plasma during the plasma-solid interaction, further to improvement of the non self-consistent technique of particle modelling, where the external electric field was obtained either from the fluid model or directly from the trajectories of charged particles and finally to efficiency of individual algorithms.

Influence of intralipid on free propofol fraction assayed in human serum albumin solutions and human plasma

It is generally assumed that only unbound drugs can reach the site of action by diffusing across the membranes and exerting pharmacological effects by interacting with receptors. Recent research has shown that the percentage of free drugs may depend on the total drug concentration. The aim of the paper is to verify whether the mentioned dependence reported for propofol also takes place in plasma and human serum albumin samples in the presence of intralipid-the medium used as a vehicle for propofol infusions and a parenteral nutrition agent. Artificial plasma samples and human plasma were spiked with intralipid or ethanolic solutions of propofol. The samples were then assayed for free propofol concentration using ultrafiltration and high performance liquid chromatography with fluorimetric detection. The decrease of the total drug concentration results in free propofol fraction increase, irrespectively of the used type of propofol solvent and sample type. The addition of intralipid causes the lowering of the overall free drug fraction with respect to the samples spiked with ethanolic solutions of the drug. The presence of intralipid does not influence the phenomenon of free propofol fraction rise at low total drug concentration. Such a rise cannot be ignored in clinical conditions when the drug is applied for sedative, antiemetic or other low-dosage purposes.

Current status of plasma emission electronics: I. Basic physical processes

This paper reviews the physical phenomena that accompany the emission of electrons and ions from plasma. The development of plasma emission electronics as an independent research field is closely associated with the name of its founder, Professor Kreindel Yu. E. The well-known advantages of plasma electron emitters (plasma cathodes) are the higher emission current density, the pulsed emission capability, and the wider range of residual gas pressures. A peculiar property of the plasma cathode is the possibility of extracting practically all electrons from plasma. The parameters of an ion and electron beam extracted from plasma carry information about the physical processes occurring in the plasma. This makes it possible to invoke emission methods to study the fundamental phenomena that take place in plasma of vacuum arc and low-pressures gas discharges.

Human plasma trans-sialidase donor and acceptor specificity.

Earlier we have isolated from human plasma desialylated low density lipoproteins (dLDL) and showed that, first, dLDL induce cholesterol esters accumulation--the main process accompanying atherosclerosis development. Second, the process of lipoprotein desialylation took place in plasma, and, finally, sialic acids removed from LDL are transferred to other serum glycoconjugates. In this study we have isolated from human plasma an enzyme transferring sialic acid residues (trans-sialidase) by affinity chromatography and studied its donor and acceptor specificity. Isolated enzyme in the presence of saccharide-acceptor can remove sialic acids from different lipoproteins, glycoproteins (fetuin, transferrin), and gangliosides (GM3, GD3, GM1, GD1a, GD1b). Plasma enzyme translocates alpha2-6, alpha2-3 and to a lower extent alpha2-8 bonded sialic acids. Sialoglycoconjugates of human serum erythrocytes, serum lipoproteins, glycoproteins, and gangliosides can serve as donors of sialic acid for trans-sialidase. Desialylated lipoproteins, especially dLDL, are more preferable sialic acid acceptors. Transferred sialic acid is found to be alpha2-6, alpha2-3, and alpha2-8 connected.

Observation of thermonuclear neutrons emitted from dense femtosecond plasma at moderate intensities

We report on the observation of neutrons resulting from a thermonuclear reaction D + D = 3He(0.82 MeV) + n(2.45 MeV), taking place in plasma created on the surface of a modified solid-state target. The plasma was produced by a 200-fs laser pulse with intensity in excess of 1016 W/cm2 and energy of only 0.3 mJ.

New kinetic instability: Oblique Alfvén fire hose

Two instabilities could take place in plasma with a bi‐Maxwellian proton distribution function with Tp‖ > Tp⊥, where Tp‖ and Tp⊥ are proton temperatures, parallel and perpendicular, respectively, to the background magnetic field. The first instability is the fire hose (or whistler fire hose), generating low‐frequency whistler waves at parallel propagation. We found a new, second instability, the Alfvén fire hose, that generates zero‐frequency waves of the Alfvén branch at strongly oblique propagation. The Alfvén fire hose has a linear growth rate comparable to or even greater than that of the whistler fire hose. The two instabilities with the same initial plasma parameters are examined via one‐dimensional hybrid simulations and turn out to have behavior very different from each other. The whistler fire hose has an overall quasi‐linear evolution, while the evolution of the Alfvén fire hose is more complicated: Initially, unstable zero‐frequency waves are gradually transformed into propagating Alfvén waves; during this process the waves are strongly damped and heat protons in a perpendicular direction. Consequently, the Alfvén fire hose is very efficient at destroying proton anisotropy.

High speed plasma diagnostics for laser plasma interaction and fusion studies

Laser plasma interaction and fusion studies involve many high speed plasma diagnostics to determine the various parameters for explaining the physical processes taking place in plasma. Detection and analysis of short-term or transient radiations (X-ray and visible) are the bases for diagnosing the physical processes occurring during laser-plasma interaction or similar radiation-emitting processes. This paper reviews the development of various high speed plasma diagnostics which are not only applicable in determining the temporal, spatial and spectral properties of X-rays for this purpose but also have wide use in various other fields of research.

From megakaryocytes to platelets: platelet morphogenesis takes place in the bloodstream.

We studied megakaryocyte processes formed in rat bone marrow and spleen, using both the transmission and scanning electron microscopes. Some processes were bulky, others slender and beaded. The bulky megakaryocyte processes developed a specialized arrangement of organelles at the site at which they entered the lumen: filaments present around the outside of the process seemed to support a central cylinder in which organelles flowed along microtubules. Megakaryocyte processes were present in platelet-rich plasma from both human and rat blood. When followed in living preparations, bulky processes developed pointed tips, elongated, and became slender and beaded. Fusiform proplatelets also were present in the platelet rich plasma, with pointed tips at both ends of what appeared to be single "beads"; we assume that the long, beaded megakaryocyte processes would have fragmented were we to have had proper culture conditions. The straight, shorter fusiform proplatelets in living preparations underwent characteristic curving and bending motions, eventually forming disk-shaped cells which sometimes had appendages. This behaviour suggests that the entire process of platelet morphogenesis takes place in plasma: megakaryocyte processes first elongate, then bead and fragment, and then curve and fuse to form disk-shaped platelets. This interpretation is strengthened by finding in freshly isolated plasma many of the shapes seen in the transformations studied in living cell preparations. The megakaryocyte processes and the proplatelets seemed to appear in plasma with a periodicity related to light and dark cycles--that is, with a circadian rhythm. In particular, megakaryocyte processes appear in human blood within a few hours after sunrise; we argue that this might be related to similar peak periods for heart attacks.

Immunohistochemical localization of lipoperoxidation products in normal human placenta

4-Hydroxynonenal (4-HNE) is a major propagation product of lipid peroxidation that is supposed to be responsible for some of the effects associated with oxidative stress in tissues. We have investigated the possible occurrence and distribution of 4-HNE-immunoreactivity in human normal placenta using immunocytochemistry. Specific immunostaining was observed in cytotrophoblast cells, syncytiotrophoblast, some cells of the villous mesenchyme and some endothelial cells of first trimester and term placentae. The detection of 4-HNE-immunoreactivity in placenta raises the question whether lipoperoxidation products are produced locally in placental cells or represent exogenous products that derive from maternal blood flow. Since trophoblastic cells and villous macrophages are provided by a scavenger receptor, it is conceivable that these cells may play a protective role with regard to the diffusion of lipoperoxidation products from the mother to the embryo. However, since a significant degree of lipid oxidative modification does not take place in plasma, it is presumed that 4-HNE is a local product of placental metabolism. In line with this hypothesis, it is proposed that maternal low density lipoproteins, which are the major source of cholesterol for placental steroid synthesis, might be oxidized by villous cells during their traversal through the villous wall.

Effect of Heparin on the Activation of Factor XI by Fibrin-bound Thrombin

Fibrin-bound thrombin is protected from inactivation by antithrombin III, while its coagulant potential is retained. In the presence of heparin, ternary complexes between thrombin, fibrin and heparin are formed. In these complexes the coagulant activity of thrombin is retained, whereas the anticoagulant activity of fibrin-bound heparin is neutralized. The limited effectiveness of heparin in the prevention of both venous thrombosis and coronary reocclusion is probably related to the protective effect of fibrin on the inactivation of thrombin by anti-thrombin III. Recently, it has been shown that factor XI can be activated by thrombin, resulting in the generation of additional thrombin via the intrinsic pathway. This additional thrombin is capable of stabilizing the clot by protecting it from fibrinolysis. We studied the effect of heparin on the activation of factor XI by fibrin-bound thrombin. First, we used fibrin monomers coupled to Sepharose to which thrombin and unfractionated heparin (UFH) were bound. Factor XI activation by thrombin was the same in the presence of fibrin-Sepharose or control-Sepharose. The addition of heparin (0.1 U/ml) resulted in a 91 and 15-fold enhancement in the presence of control-Sepharose and fibrin-Sepharose, respectively. Next, we added complexes of heparin, thrombin and fibrin monomer to factor XII and XI double-deficient plasma in the presence or absence of a reconstituting amount of factor XI. In the presence of factor XI, additional fibrin formation was observed indicating that factor XI activation by thrombin in complex with fibrin and heparin can take place in plasma. We then studied the effect of other heparin-like anticoagulants on the thrombin-mediated factor XI activation. UFH enhanced thrombin-mediated factor XI activation 68-fold, LMWH (low molecular weight heparin, Fragmin) 12-fold, danaparoid (Orgaran) 3-fold, while the pentasaccharide ORG 31540 did not result in an enhancement. Binding studies of these anticoagulants to fibrin-Sepharose showed that LMWH bound with approximately the same affinity as UFH, while danaparoid and the pentasaccharide did not bind to fibrin. We conclude that fibrin-bound thrombin is capable of factor XI activation. Furthermore, heparin bound in a complex with fibrin can act as a cofactor for this activation. This factor XI activation capacity may play a role in the limited effectiveness of heparin. Provided that thrombin-mediated factor XI activation plays an important role in vivo, danaparoid and especially the pentasaccharide may be better anticoagulants than UFH and LMWH.

Feedback Activation of Factor XI by Thrombin in Plasma Results in Additional Formation of Thrombin That Protects Fibrin Clots From Fibrinolysis

Recently, an alternative pathway for factor XI activation has been described in which factor XI is activated by thrombin. Patients with a factor XI deficiency bleed mostly from tissues with high local fibrinolytic activity. Therefore, the role of thrombin-mediated factor XI activation in both fibrin formation and fibrinolysis was studied in a plasma system. Clotting was induced by the addition of tissue factor or thrombin to recalcified plasma in the presence or absence of tissue-type plasminogen activator, after which clot formation and lysis were measured using turbidimetry. Thrombin-mediated activation of factor XI was found to take place in plasma under physiologic conditions in the absence of a dextran sulfate-like cofactor. At high tissue factor concentrations, no effect of factor XI was seen on the rate of fibrin formation. Decreasing amounts of tissue factor resulted in a gradually increasing contribution of factor XI to the rate of fibrin formation. In addition, thrombin-mediated factor XI activation resulted in an inhibition of tissue-type plasminogen activator-induced lysis of the clot. This inhibition occurred even at tissue factor concentrations at which no effect of factor XI was observed on fibrin formation. Trace amounts of activated factor XI (1.25 pmol/L, representing 0.01% activation) were capable of completely inhibiting fibrinolysis in our system. The inhibitory effect was found to be mediated by thrombin that is additionally generated in a factor XI-dependent manner via the intrinsic pathway and is capable of protecting the clot against lysis. We also observed that formation of additional thrombin continued after the clot had been formed. We conclude that thrombin-mediated factor XI activation can take place in plasma. The presence of factor XI during coagulation results in the formation of additional thrombin within the clot capable of protecting this clot from fibrinolytic attack. The large amounts of thrombin that are formed by the intrinsic pathway via factor XI may play an important role in the procoagulant and thrombogenic state of clots and may therefore have important clinical and therapeutic implications.

Feedback activation of factor XI by thrombin in plasma results in additional formation of thrombin that protects fibrin clots from fibrinolysis

Recently, an alternative pathway for factor XI activation has been described in which factor XI is activated by thrombin. Patients with a factor XI deficiency bleed mostly from tissues with high local fibrinolytic activity. Therefore, the role of thrombin-mediated factor XI activation in both fibrin formation and fibrinolysis was studied in a plasma system. Clotting was induced by the addition of tissue factor or thrombin to recalcified plasma in the presence or absence of tissue-type plasminogen activator, after which clot formation and lysis were measured using turbidimetry. Thrombin-mediated activation of factor XI was found to take place in plasma under physiologic conditions in the absence of a dextran sulfate-like cofactor. At high tissue factor concentrations, no effect of factor XI was seen on the rate of fibrin formation. Decreasing amounts of tissue factor resulted in a gradually increasing contribution of factor XI to the rate of fibrin formation. In addition, thrombin-mediated factor XI activation resulted in an inhibition of tissue-type plasminogen activator-induced lysis of the clot. This inhibition occurred even at tissue factor concentrations at which no effect of factor XI was observed on fibrin formation. Trace amounts of activated factor XI (1.25 pmol/L, representing 0.01% activation) were capable of completely inhibiting fibrinolysis in our system. The inhibitory effect was found to be mediated by thrombin that is additionally generated in a factor XI-dependent manner via the intrinsic pathway and is capable of protecting the clot against lysis. We also observed that formation of additional thrombin continued after the clot had been formed. We conclude that thrombin-mediated factor XI activation can take place in plasma. The presence of factor XI during coagulation results in the formation of additional thrombin within the clot capable of protecting this clot from fibrinolytic attack. The large amounts of thrombin that are formed by the intrinsic pathway via factor XI may play an important role in the procoagulant and thrombogenic state of clots and may therefore have important clinical and therapeutic implications.