Generation and interaction of intense counterpropagating plasma flows

Results are presented from experimental studies of the parameters of two counterpropagating (colliding) plasma flows generated by discharges in crossed electric and magnetic fields. It is shown that the conversion efficiency of the energy deposited in the discharges into the energy of directed plasma flows is 0.3–0.6. For discharge current pulses with a duration of ∼10 μs, the energy flux density in the plasma flow reaches ∼10 J/cm² and the total energy of the flow is on the order of 300 J. The density of deuterons in the flows is ∼10¹⁵ cm⁻³, and the flow velocity is ≤2×10⁷ cm/s. The total number of particles carried by the flows is about 10¹⁹. The possibility of using counterpropagating plasma flows to study reactions involving light nuclei (dd, pd, dt, and dHe reactions) in the range of ultralow collision energies is discussed. __________ Translated from Fizika Plazmy, Vol. 29, No. 8, 2003, pp. 714–721. Original Russian Text Copyright ? 2003 by Dudkin, Nechaev, Padalko, Bystritsky, Stolupin, Bystritskii, Voznyak.     

Volume flows across gallbladder epithelium induced by small hydrostatic and osmotic gradients

Summary The hydraulic conductivity of rabbit gallbladder epithelium has been studied using a continuous volumetric method based on capacitance measurements. The time resolution for measuring osmotic flows is in the range of seconds. Volume flows have been induced by osmotic gradients between 0 and 100 mosmol. In this range the flow-force relation is linear and theP _f value is 9.3×10^–3 cm/sec. After correction for solute polarization effects, theP _f value amounts to 0.05 cm/sec. The observed flow is constant between 5 sec up to 20 min after a sudden increase in the osmolarity of the mucosal solution. The wet weight of the gallbladder tissue decreases by 22% and increases by 30% during osmotic flows from serosa to mucosa and from mucosa to serosa, respectively. Volume flows induced by hydrostatic pressure gradients on the mucosal surface are linearly related to the driving forces between 0 and 40 mbar. TheP _f value is 0.15 cm/sec. The volume flows are constant between 2 sec and 15 min after pressure application. The flow-force relation for pressure gradients on the serosal surface is markedly nonlinear for gradients greater than 5 mbar. Below 5 mbar theP _f value is 4.5 cm/sec. From electrical measurements, e.g., resistance and streaming potentials, and from flux studies with inulin and polyethylene glycol 4000, it is concluded that hydrostatic and osmotic gradients are not comparable when they are applied to gallbladder epithelium. They induce volume flows across different pathways, e.g., osmosis predominantly across the cellular route and pressure filtration predominantly across paracellular routes.     

High-Power X-Ray Line Radiation of the Plasma Produced in a Collision of High-Energy Plasma Flows

Results are presented from experimental studies of a pulsed source of soft X-ray (SXR) emission with photon energies in the range of 0.4–1 keV and an output energy of 2–10 kJ. SXR pulses with a duration of 10–15 μs were generated in collisions of two plasma flows propagating toward one another in a longitudinal magnetic field. The plasma flows with velocities of (2–4) × 10⁷ cm/s and energy contents of 70–100 kJ were produced by two electrodynamic coaxial accelerators with pulsed gas injection. Nitrogen and neon, as well as their mixtures with deuterium, were used as working gases. The diagnostic equipment is described, and the experimental results obtained under different operating conditions are discussed. In particular, X-ray spectroscopy was used to study the high-temperature plasma produced in a collision of two plasma flows. The observed intensities of spectral lines are compared with the results of detailed kinetic calculations performed in a steady-state approximation. The calculations of the nitrogen and neon kinetics have shown that the electron temperature of a nitrogen plasma can be most conveniently determined from the intensity ratio of the resonance lines of He- and H-like nitrogen ions, while that of a neon plasma, from the intensity ratio between the resonance line of He-like Ne IX ions and the 3p?2s line of Li-like Ne VIII ions. In the experiments with plasma flows containing nitrogen ions, the electron temperature was found to be ≈120 eV, whereas in the experiments with plasma flows containing neon ions, it was 160–170 eV.     

Measurements of the electron density and degree of plasma ionization in a plasma target based on a linear electric discharge in hydrogen

Laser interferometry methods were used to measure the density of free electrons and degree of plasma ionization in a hydrogen target intended for experiments on determining energy losses of heavy ion beams in an ionized matter. It is shown that the linear electron density can be varied in the range from 3.3 × 10¹⁷ to 1.3 × 10¹⁸ cm^?2 by varying the initial plasma parameters (the hydrogen pressure in the target and the discharge current). The error in measuring the linear electron density in the entire range of the varied plasma parameters was less than 1%. The maximum degree of plasma ionization achieved at the initial gas pressure of 1 mbar was 0.62 ± 0.05.     

Volatile organic compounds evaporation chamber for the simulation of gas effluents in laboratory research

A device for mixing air with a pollutant (e.g., volatile organic compounds) is presented, which is based on principles of evaporation and diffusion. A wide-necked flask containing an aluminium cylindrical body, allows the evaporating area to be preset to 5.75 cm² or 23.03 cm². The distance from the evaporating surface to the region of passage of the air is adjustable between 0 and 8 cm, which allows to assay a wide range of evaporation flows (for toluene: 1.5 to 200 mg/minute).     

Equilibrium,stability, and estimate of plasma confinement in the L-5 compact torsatron

Possible parameters of a plasma in a compact torsatron that is to be constructed at the Prokhorov Institute of General Physics, Russian Academy of Sciences (the L-5 project) are discussed. The properties of the original vacuum configuration created by the external coils are described. The equilibrium of a plasma with a free boundary and the stability of local MHD modes are investigated. The effective magnetic field ripples and the structural factor of the bootstrap current in the 1/ν regime are calculated, as well as collisionless losses of trapped α-particles. The dependence of these properties on the relative plasma pressure is examined. It is shown that the maximum possible <β> (the ratio of the gas-kinetic plasma pressure to the magnetic field pressure, averaged over the volume of the plasma column) consistent with equilibrium exceeds 2.0%. The power of the external sources for plasma heating in the anticipated operating modes is estimated using the present-day scalings. The efficiency of different methods for calculating the magnetic fields and, accordingly, the magnetic surfaces created by the external coils is analyzed in the Appendix.     

Neutron emission generated in the collision of plasma flows in the presence of an external magnetic field

Results are presented from experimental studies of the neutron emission generated in the collision of deuterium plasma flows produced in discharges in crossed E × H fields and propagating in opposite directions in a neutral gas across an external magnetic field. It is shown that the interaction of oppositely propagating deuterium plasma flows gives rise to the generation of soft X-ray emission and neutron emission from the dd reaction (dd → ³He + n) and is accompanied by an almost complete depolarization of the flows and rapid variations in the magnetic field (at a rate of ～10¹¹ G/s). The measurements were performed at energies and velocities of the flows of up to 600 J and 3.5 × 10⁷ cm/s, respectively. The plasma density in each flow was ～10¹⁵ cm^?3. The upper estimates for the astrophysical S factor and the effective cross sections of the dd reaction obtained from our measurements are compared to theoretical calculations and to the results of experiments performed in the MIG high-current accelerator (Institute of High-Current Electronics, Russian Academy of Sciences, Tomsk).     

Peculiarities of the beam-plasma discharge development in high-pressure gas and prospects of its application

The dynamics of a stationary beam-plasma discharge at the neutral gas pressure of 10⁻³-1 Torr is investigated. Three discharge modes have been revealed: two of them are characterized by novel properties and have not been studied as of yet. Dissipative instabilities with different increments have been found. The generation of ion flows has been studied and the experiments on “dry” cleaning of the metal specimen surfaces using them have been carried out. The pressure ranges in a neutral gas at which the discharge can be efficiently applied in nonequilibrium plasma chemistry are given.     

Plasma decay in high-voltage nanosecond discharges in oxygen-containing mixtures

Plasma decay in high-voltage nanosecond discharges in CO₂: O₂ and Ar: O₂ mixtures at room gas temperature and a pressure of 10 Torr is studied experimentally and theoretically. The time dependence of the electron density during plasma decay is measured using microwave interferometry. The time evolution of the charged particle density, ion composition, and electron temperature is simulated numerically. It is shown that, under the given conditions, the discharge plasma is dominated for the most time by O ₂ ⁺ ions and plasma decay is determined by dissociative and three-body electron?ion recombination. As in the previous studies performed for air and oxygen plasmas, agreement between measurements and calculations is achieved only under the assumption that the rate of three-body recombination of molecular ions is much greater than that for atomic ions. The values of the rate constant of three-body recombination of electrons with О₂ ⁺ ions in a wide range of electron temperatures (500–5500 K), as well as for thermal (300 K) electrons, are obtained by processing the experimental results.     

Rapid quantitation of free fatty acids in human plasma by high-performance liquid chromatography

We report a rapid and sensitive method for separation and quantitation of free fatty acids (FFAs) in human plasma using high-performance liquid chromatography (HPLC). Two established techniques of lipid extraction were investigated and modified to achieve maximal FFA recovery in a reasonably short time period. A modified Dole extraction method exhibited greater recovery (90%) and short processing times (30 min) compared to the method of Miles et al. Reversed-phase HPLC using UV detection was used for plasma FFA separation and quantitation. Two phenacyl ester derivatives, phenacyl bromide and p-bromophenacyl bromide, were investigated in order to achieve optimal separation of individual plasma FFAs (saturated and unsaturated) with desirable detection limits. Different chromatographic parameters including column temperature, column type and elution profiles (isocratic and gradient) were tested to achieve optimal separation and recovery of fatty acids. Phenacyl bromide esters of plasma fatty acids were best resolved using an octadecylsilyl column with endcapped silanol groups. An isocratic elution method using acetonitrile–water (83:17) at 2 ml/min with UV detection at 242 nm and a column temperature of 45°C was found to optimally resolve the six major free fatty acids present in human plasma (myristic [14:0], palmitic [16:0], palmitoleic [16:1], stearic [18:0], oleic [18:1] and linoleic [18:2]), with a run time of less than 35 min and detection limits in the nmol range. The entire process including plasma extraction, pre-column derivatization, and HPLC quantitation can be completed in 90 min with plasma samples as small as 50 μl. Over a wide physiological range, plasma FFA concentrations determined using our HPLC method agree closely with measurements using established TLC–GC methods (r²≥0.95). In addition, by measuring [¹⁴C] or [³H] radioactivity in eluent fractions following HPLC separation of plasma FFA, this method can also quantitate rates of FFA turnover in vivo in human metabolic studies employing isotopic tracers of one or more fatty acids.     

Determination of the retinobenzoic acid derivative Am580 in rat plasma by high-performance liquid chromatography

A specific liquid chromatographic method for the determination of 4-[[(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)carbonyl]amino]benzoic acid (Am580) in rat plasma is described. The procedure includes one-step isolation of the compound and the internal standard (naphtol AS) from protein precipitated with acetonitrile, resolution on a reversed-phase column (Supelcosil LC18-DB, 5 μm) with water-acetonitrile-methanol-n-butanol (45:40:14:1, v/v) containing 65 mM ammonium acetate as elution system and UV absorbance detection at 280 nm. The assay was linear over a wide range (25–5000 ng ml⁻¹) and the limit of quantitation was 25 ng ml⁻¹ using 0.2 ml of plasma. It was precise and reproducible enough for pharmacokinetic studies. Application to a preliminary disposition study in the rat indicated that Am580 was characterized by a relatively large apparent volume of distribution (1.1–1.5 l kg⁻¹) and small clearance (8.8–9.7 ml min⁻¹ kg⁻¹). Its pharmacokinetic behaviour was linear within the dose range considered (2 and 10 mg kg⁻¹, i.p.).     

Symplasmic transport of water along the root depends on pressure

The gradient NMR method was applied to study intercellular water flows in root segments of maize (Zea mays L.) under disturbance of root hydrodynamic system by the increase in external pressure up to 4 MPa. The rate of intercellular water flows along the root symplast was found to depend on the magnitude and dynamics of pressure changes. Based on the previously predicted cupola-shaped dependency of water flow on the aperture of plasmodesmal neck constrictions, we assume that the external pressure stimulates (via cytosolic calcium) the activity of contractile structures localized in the neck regions of plasmodesmata. Cells of Chlorella vulgaris were taken for comparison since their water relations and cell structure differ strongly from the root cells of maize. The results show that the diffusional water flow in Chlorella is independent of external pressure both in intact cells and in algae, whose plasma membrane was artificially permeabilized.     

Measurement of plasma uracil using gas chromatography–mass spectrometry in normal individuals and in patients receiving inhibitors of dihydropyrimidine dehydrogenase

A sensitive gas chromatographic–mass spectrometric method is described for reliably measuring endogenous uracil in 100 μl of human plasma. Validation of this assay over a wide concentration range, 0.025 μM to 250 μM (0.0028 μg/ml to 28 μg/ml), allowed for the determination of plasma uracil in patients treated with agents such as eniluracil, an inhibitor of the pyrimidine catabolic enzyme, dihydropyrimidine dehydrogenase. Calibration standards were prepared in human plasma using the stable isotope, [¹⁵N₂]uracil, to avoid interference from endogenous uracil and 10 μM 5-chlorouracil was added as the internal standard.     

Microfluidic Mixers for Studying Protein Folding

The process by which a protein folds into its native conformation is highly relevant to biology and human health yet still poorly understood. One reason for this is that folding takes place over a wide range of timescales, from nanoseconds to seconds or longer, depending on the protein¹. Conventional stopped-flow mixers have allowed measurement of folding kinetics starting at about 1 ms. We have recently developed a microfluidic mixer that dilutes denaturant ~100-fold in ~8 μs². Unlike a stopped-flow mixer, this mixer operates in the laminar flow regime in which turbulence does not occur. The absence of turbulence allows precise numeric simulation of all flows within the mixer with excellent agreement to experiment^3-4.Laminar flow is achieved for Reynolds numbers Re ≤100. For aqueous solutions, this requires micron scale geometries. We use a hard substrate, such as silicon or fused silica, to make channels 5-10 μm wide and 10 μm deep (See Figure 1). The smallest dimensions, at the entrance to the mixing region, are on the order of 1 μm in size. The chip is sealed with a thin glass or fused silica coverslip for optical access. Typical total linear flow rates are ~1 m/s, yielding Re~10, but the protein consumption is only ~0.5 nL/s or 1.8 μL/hr. Protein concentration depends on the detection method: For tryptophan fluorescence the typical concentration is 100 μM (for 1 Trp/protein) and for FRET the typical concentration is ~100 nM.The folding process is initiated by rapid dilution of denaturant from 6 M to 0.06 M guanidine hydrochloride. The protein in high denaturant flows down a central channel and is met on either side at the mixing region by buffer without denaturant moving ~100 times faster (see Figure 2). This geometry causes rapid constriction of the protein flow into a narrow jet ~100 nm wide. Diffusion of the light denaturant molecules is very rapid, while diffusion of the heavy protein molecules is much slower, diffusing less than 1 μm in 1 ms. The difference in diffusion constant of the denaturant and the protein results in rapid dilution of the denaturant from the protein stream, reducing the effective concentration of the denaturant around the protein. The protein jet flows at a constant rate down the observation channel and fluorescence of the protein during folding can be observed using a scanning confocal microscope⁵.     

Parameters of radiation processes in the microwave resonant plasma

This work presents results of experimental studies of the spectral and photometric characteristics of optical radiation generated by a pulse-periodic microwave discharge close to ECR (2.45 GHz, average power of up to 200 W, argon pressure of 10^–4–10^–1 Torr). Under these conditions, dense (n _e = 10¹⁰–4 × 10¹¹ cm^–3) low-temperature (T _e = 3–5 eV) plasma is produced in the working volume at an ionization rate of 10^–3–5 × 10^–5. It is shown that the increase in the electron density near the upper boundary of the pressure range at a constant level of the input power leads to a drastic change in the type and spectral composition of plasma radiation and a jumplike increase in the light flux. The results of probe and optical measurements made it possible to determine the range of the operating parameters defining the character and parameters of the radiation processes under study.     

Imaging of spatial distributions of the millimeter wave intensity by using visible continuum radiation from a discharge in a Cs–Xe mixture. Part I: Review of the method and its fundamentals

The first part of the review is presented which is dedicated to the time-resolved method of imaging and measuring the spatial distribution of the intensity of millimeter waves by using visible continuum (VC) emitted by the positive column (PC) of a dc discharge in a mixture of cesium vapor with xenon. The review focuses on the operating principles, fundamentals, and applications of this new technique. The design of the discharge tube and experimental setup used to create a wide homogeneous plasma slab with the help of the Cs–Xe discharge at a gas pressure of 45 Torr are described. The millimeter-wave effects on the plasma slab are studied experimentally. The mechanism of microwave-induced variations in the VC brightness and the causes of violation of the local relation between the VC brightness and the intensity of millimeter waves are discussed. Experiments on the imaging of the field patterns of horn antennas and quasi-optical beams demonstrate that this technique can be used for good-quality imaging of millimeter-wave beams in the entire millimeter-wavelength band. The method has a microsecond temporal resolution and a spatial resolution of about 2 mm. Energy sensitivities of about 10 μJ/cm² in the Ka-band and about 200 μJ/cm² in the D-band have been demonstrated.     

Helicon plasma in a nonuniform magnetic field

The distributions of the electron density in a plasma produced by helicon waves and the correspond-ing wave amplitudes and phases are studied experimentally. The measurements were carried out in an argon plasma at a pressure of 3 mtorr and at an input RF power of up to 600 W. The magnetic field was caried in the range from 0 to 200 G. The efficiency of plasma production in both uniform and nonuniform fields is investigated. It is shown that, in a nonuniform magnetic field, the electron density can be substantially increased (up to 5×10¹² cm^?3) by placing an antenna in the region in which the magnetic field is weaker than in the main plasma.     

Validation of an analytical method for a potent antitumor agent, TZT-1027, in plasma using liquid chromatography–mass spectrometry

A sensitive and specific analytical method for a potent antitumor agent, TZT-1027, in plasma has been developed using liquid chromatography–mass spectrometry (LC–MS) with [²H₄]TZT-1027 as an internal standard (I.S.). A plasma sample was purified by solid-phase extraction on a C₁₈ cartridge, followed by solvent extraction with diethyl ether. The extract was then injected into the LC–MS system. Chromatography was carried out on a C₁₈ reversed-phase column using acetonitrile–0.05% trifluoroacetic acid (TFA) (55:45) as a mobile phase. Mass spectrometric analysis was performed in atmospheric pressure chemical ionization (APCI) mode with positive ion detection, and the protonated molecular ions ([M+H]⁺) of TZT-1027 and I.S. were monitored to allow quantitation. The method was applied to the determination of TZT-1027 in human, monkey, dog, rat and mouse plasma. As far as the sample preparation was concerned, good recoveries (73.5–99.1%) were obtained. The calibration curves were linear over the range of 0.25–100 ng per 1 ml of human, dog and rat plasma, per 0.5 ml of monkey plasma, and per 0.1 ml of mouse plasma. From the intra- and inter-day accuracy and precision, the present method satisfies the accepted criteria for bioanalytical method validation. TZT-1027 was stable when stored below −15°C for 6 months in human plasma and for 3 weeks in plasma from other species. TZT-1027 was also stable in plasma through at least three freeze–thaw cycles.     

Determination of ZD9583, a thromboxane receptor antagonist, in human plasma and urine by liquid chromatography atmospheric pressure chemical ionization tandem mass spectrometry

A liquid chromatography–atmospheric pressure chemical ionization tandem mass spectrometry (LC–APCI-MS–MS) method is described for the determination of a thromboxane receptor antagonist (4Z)-6-((2S,4S,5R)-2-(1-(2-cyano-4-methylphenoxy)-1-methylethyl)-4-(3-pyridyl)-3-dioxan-5-yl)hex-4-enoic acid (ZD9583, I) in human plasma and urine. Proteins in plasma and urine samples are precipitated using acidified acetonitrile. The resulting supernatant is chromatographed on a C₈ reversed-phase chromatography column. Following the diversion of the solvent front from the mass spectrometer by a switching valve, the column eluate is passed on to the mass spectrometer via a heated nebulizer interface where the analyte is detected by multiple reaction monitoring (MRM). The method has a chromatographic run time of less than 2 min, a linear calibration curve with a range of 1–500 ng ml⁻¹ and intra- and inter-day precision estimates of less than 10% over the calibration range.