Glow discharge with electrostatic confinement of electrons in a chamber bombarded by fast electrons

A metal substrate is immersed in plasma of glow discharge with electrostatic confinement of electrons inside the vacuum chamber volume V ≈ 0.12 m³ filled with argon or nitrogen at pressures 0.005–5 Pa, and dependence of discharge characteristics on negative substrate potential is studied. Emitted by the substrate secondary electrons bombard the chamber walls and it results in electron emission growth of the chamber walls and rise of gas ionization intensity inside the chamber. Increase of voltage U between the chamber and the substrate up to 10 kV at a constant discharge current I _d in the anode circuit results in a manifold rise of current I in the substrate circuit and decrease of discharge voltage U _d between the anode and the chamber from hundreds to tens of volts. At pressure p < 0.05 Pa nonuniformity of plasma density does not exceed ∼10%. Using the Child-Langmuir law, as well as measurement results of sheath width d between homogeneous plasma and a lengthy flat substrate dependent on voltage U ion current density j _i on the substrate surface and ion-electron emission coefficient γ _i are calculated. After the current in circuit of a substrate made of the same material is measured, the γ _i values may be used to evaluate the average dose of ion implantation. The rate of dose rise at a constant high voltage U is by an order of magnitude higher than in known systems equipped with generators of square-wave high-voltage pulses. Application to the substrate of 10-ms-wide sinusoidal high-voltage pulses, which follow each other with 100-Hz frequency, results in synchronous oscillations of voltage U and ion current I _i in the substrate circuit. In this case variation of the sheath width d due to oscillations of U and Ii is insignificant and d does not exceed several centimeters thus enabling substrate treatment in a comparatively small vacuum chamber.     

Filling the vacuum chamber of a technological system with homogeneous plasma using a stationary glow discharge

Experimental study of a glow discharge with electrostatic confinement of electrons is carried out in the vacuum chamber volume V ≈ 0.12 m³ of a technological system “Bulat-6” in argon pressure range 0.005–5 Pa. The chamber is used as a hollow cathode of the discharge with the inner surface area S ≈ 1.5 m². It is equipped with two feedthroughs, which make it possible to immerse in the discharge plasma interchangeable anodes with surface area S _a ranging from ∼0.001 to ∼0.1 m², as well as floating electrodes isolated from both the chamber and the anode. Dependences of the cathode fall U _c = 0.4−3 kV on the pressure p at a constant discharge current in the range I = 0.2−2 A proved that aperture of the electron escape out of the electrostatic trap is equal to the sum S _o = S _a + S _f of the anode surface S _a and the floating electrode surface S _f . The sum S _o defines the lower limit p _o of the pressure range, in which U _c is independent of p. At p < p _o the cathode fall U _c grows up dramatically, when the pressure decreases, and the pressure p tends to the limit p ^ex, which is in fact the discharge extinction pressure. At p ≈ p ^ex electrons emitted by the cathode and the first generation of fast electrons produced in the cathode sheath spend almost all their energy up to 3 keV on heating the anode and the floating electrode up to 600–800°C and higher. In this case the gas in the chamber is being ionized by the next generations of electrons produced in the cathode sheath, their energy being one order of magnitude lower. When S _a < (2m/M)^1/2 S, where m is the electron mass and M is the ion mass, the anode may be additionally heated by plasma electrons accelerated by the anode fall of potential U _a up to 0.5 kV.     

Experimental and theoretical studies of the spatial distribution of the ionization rate in a non-self-sustained discharge controlled by a fast electron beam

The spatial distribution of the current density of fast electrons and the ionization rate in a gap filled with atmospheric-pressure air under the conditions of a non-self-sustained discharge controlled by a fast electron beam were investigated. The experiments were carried out in a gas-discharge chamber with a grid electrode arranged in parallel to the exit window of the ionization source. Spatial variations in the current density of fast electrons resulting from the grid were measured. The propagation of the electron beam through the discharge system was simulated numerically by the Monte Carlo method in the so-called “effective collision” approximation. The calculated results agree well with the experimental data.     

Beams of fast neutral atoms and molecules in low-pressure gas-discharge plasma

Fast neutral atom and molecule beams have been studied, the beams being produced in a vacuum chamber at nitrogen, argon, or helium pressure of 0.1–10 Pa due to charge-exchange collisions of ions accelerated in the sheath between the glow discharge plasma and a negative grid immersed therein. From a flat grid, two broad beams of molecules with continuous distribution of their energy from zero up to e(U + U _c ) (where U is voltage between the grid and the vacuum chamber and U _c is cathode fall of the discharge) are propagating in opposite directions. The beam propagating from the concave surface of a 0.2-m-diameter grid is focused within a 10-mm-diameter spot on the target surface. When a 0.2-m-diameter 0.2-m-high cylindrical grid covered by end disks and composed of parallel 1.5-mm-diameter knitting needles spaced by 4.5 mm is immersed in the plasma, the accelerated ions pass through the gaps between the needles, turn inside the grid into fast atoms or molecules, and escape from the grid through the gaps on its opposite side. The Doppler shift of spectral lines allows for measuring the fast atom energy, which corresponds to the potential difference between the plasma inside the chamber and the plasma produced as a result of charge-exchange collisions inside the cylindrical grid.     

Diagnostics of plasma produced by femtosecond laser pulse impact upon a target with an internal nanostructure

X-ray diagnostics of the interaction of femtosecond laser pulses with intensities of 10¹⁶–10¹⁸ W/cm² with CO₂ clusters and frozen nanosize water particles is carried out. The stage of cluster expansion and the formation of a plasma channel, which governs the parameters of the formed X-ray radiation source and accelerated ion flows, is studied. The measurements are based on recording spatially resolved X-ray spectra of H- and He-like oxygen ions. Utilization of Rydberg transitions for spectra diagnostics makes it possible to determine plasma parameters on a time scale of t ∼ 10 ps after the beginning of a femtosecond pulse. The role of the rear edge of the laser pulse in sustaining the plasma temperature at a level of ∼100 eV in the stage of a nonadiabatic cluster expansion is shown. The analysis of the profiles and relative intensities of spectral lines allows one to determine the temperature and density of plasma electrons and distinguish the populations of “thermal” ions and ions that are accelerated up to energies of a few tens of kiloelectronvolts. It is shown that the use of solid clusters made of frozen nanoscale water droplets as targets leads to a substantial increase in the number of fast He-like ions. In this case, however, the efficiency of acceleration of H-like ions does not increase, because the time of their ionization in plasma exceeds the time of cluster expansion.     

Distribution of matter in the current-carrying plasma and dense core of the discharge channel formed upon electrical wire explosion

Distribution of matter in the discharge channel formed upon a nanosecond electrical explosion of a single wire in air and vacuum was studied experimentally. Simultaneous use of optical, UV, and X-ray diagnostics made it possible to distinguish qualitatively different regions of the discharge channel, such as the current-carrying layers and the region occupied by a weakly conducting cold plasma. Several series of experiments with 25-μm-diameter 12-mm-long wires made of different materials were performed. The charging voltage and the current amplitude were varied in the ranges of U ₀ = 10–20 kV and I _max ∼ 5–10 kA, respectively. Explosion regimes with a current pause and with and without current interruption, as well as with wire preheating in air and vacuum, were studied. Shadow and schlieren images of the discharge channel were obtained using optical probing at the second harmonic of a YAG: Nd⁺³ laser (λ = 0.532 μm, τ ∼ 10 ns). In the experiments carried out in vacuum, X-ray images of the discharge channel were also obtained using an X-pinch as a point source of probing radiation and UV images were recorded using a four-frame MCP camera.     

Study of the core-corona structure formed during the explosion of an aluminum wire in vacuum

The time evolution of the matter parameters and current distribution in the discharge channel formed during a nanosecond explosion of a 25-μm-diameter 12-mm-long aluminum wire was studied in a series of experiments with the following parameters: the discharge voltage was U ₀ = 20 kV, the current amplitude was I _max ∼ 8 kA, and the current rise rate was dI/dt ∼ 40 A/ns. Optical shadow and schlieren images of the discharge channel were obtained using the second harmonic of a YAG: Nd⁺³ laser, and UV images of the discharge channel self-radiation were recorded using a four-frame camera with a microchannel plate. The process of aluminum wire explosion was simulated numerically (including simulations performed from the “cold start”). The numerical results were compared with the experimental data.     

Heterothermy in an Australian passerine, the Dusky Woodswallow (Artamus cyanopterus)

Information regarding passerine heterothermy and torpor is scant, although many species are small and must cope with a fluctuating food supply and presumably would benefit from energy savings afforded by torpor. We studied whether insectivorous Dusky Woodswallows (Artamus cyanopterus; ∼35 g) enter spontaneous torpor (food ad libitum) when held outdoors as a pair in autumn/winter. Woodswallows displayed pronounced and regular daily fluctuations in body temperature (T _b) over the entire study period. The mean T _b ranged from ∼39°C to 40°C (photophase, day time) and ∼33°C to 36°C (scotophase, night time). However, on 88% of bird nights, nocturnal T _b minima fell to < 35°C. The lowest T _b observed in air was 29.2°C. However, when a bird fell into water its T _b dropped further to ∼22°C; this T _b was regulated for several hours and the bird survived. Our observations suggest that heterothermy is a normal part of the daily thermal regime for woodswallows to minimise energy expenditure. Spontaneous nocturnal torpor in captive woodswallows suggests that torpor in the wild may be more pronounced than recorded here because free-living birds are likely challenged by both low food availability and adverse weather.     

Compressive and rarefactive DIA solitons beyond the KdV limit

The modified Gardner equation (MGE), showing the existence of compressive and rarefactive dust-ion-acoustic (DIA) solitons in a nonplanar dusty plasma (containing inertial ions, Boltzmann electrons, and negatively charged stationary dust) beyond the KdV Korteweg-de Vries (KdV) limit, is derived and numerically solved. The basic features of the compressive and rarefactive cylindrical and spherical DIA solitons, which are found to exist beyond the KdV limit, i.e., exist for μ ∼ 2/3 (where μ = Z _n n _d0/n _i0, z _d is the number of electrons residing onto the dust grain surface, n _d0(n _i0) is the dust (ion) number density at equilibrium, and μ ∼ 2/3 means that μ is not equal to 2/3, but it is around 2/3) are identified. These solitons (which can be referred to as DIA Gardner solitons (DIA-GSs)) are completely different from the KdV solitons because μ = 2/3 corresponds to the vanishing of the nonlinear coefficient of the KdV equation, and μ ∼ 2/3 corresponds to extremely large amplitude KdV solitons for which the validity of the reductive perturbation method breaks down. It is also shown that the properties of the nonplanar (cylindrical and spherical) DIA-GSs are significantly different from those of the one dimensional planar ones.     

The effects of detergents DDM and β-OG on the singlet excited state lifetime of the chlorophyll a in cytochrome b6f complex from spinach chloroplasts

The singlet excited state lifetime of the chlorophyll a (Chi a) in cytochrome b6f (Cyt b6f) complex was reported to be shorter than that of free Chl a in methanol, but the value was different for Cyt b6f complexes from different sources (～200 and ～600 ps are the two measured results). The present study demonstrated that the singiet excited state lifetime is associated with the detergents n-dodecyl-β-D-maltoside (DDM) and n-octyl-β-D-glucopyranoside (β-OG), but has nothing to do with the different sources of Cyt b6f complexes. Compared with the Cyt b6f dissolved in β-OG, the Cyt b6f in DDM had a lower fluorescence yield, a lower photodegradation rate of Chl a, and a shorter lifetime of Chl a excited state. In short, the singlet excited state lifetime, ～200 ps, of the Chl a in Cyt b6f complex in DDM is closer to the true in vivo.     

The effects of detergents DDM and β-OG on the singlet excited state lifetime of the chlorophyll a in cytochrome b6f complex from spinach chloroplasts

The singlet excited state lifetime of the chlorophyll a (Chl a) in cytochrome b ₆ f (Cyt b ₆ f) complex was reported to be shorter than that of free Chl a in methanol, but the value was different for Cyt b ₆ f complexes from different sources (∼200 and ∼600 ps are the two measured results). The present study demonstrated that the singlet excited state lifetime is associated with the detergents n-dodecyl-β-D-maltoside (DDM) and n-octyl-β-D-glucopyranoside (β-OG), but has nothing to do with the different sources of Cyt b ₆ f complexes. Compared with the Cyt b ₆ f dissolved in β-OG, the Cyt b ₆ f in DDM had a lower fluorescence yield, a lower photodegradation rate of Chl a, and a shorter lifetime of Chl a excited state. In short, the singlet excited state lifetime, ∼200 ps, of the Chl a in Cyt b ₆ f complex in DDM is closer to the true in vivo.     

Calcium Channel Current in Rat Dental Pulp Cells

Voltage-gated Ca²⁺ currents in early-passage rat dental pulp cells were studied using whole-cell patch-clamp techniques. With Ba²⁺ as the charge carrier, two prominent inwardly-directed currents, I _f and I _s , were identified in these cells that could be distinguished on the basis of both kinetics and pharmacology. I _f was activated by membrane depolarizations more positive than −30 mV, and displayed fast inactivation kinetics, while I _s was activated by steeper depolarizations and inactivated more slowly. At peak current, time constants of inactivation for I _f and I _s were ∼17 vs.∼631 msec. Both I _f and I _s could be blocked by lanthanum. By contrast, only I _s was sensitive to either Bay-K or nifedipine, a specific agonist and antagonist, respectively, of L-type Ca²⁺ channels. I _s was also blocked by the peptide omega-Conotoxin GVIA. Taken together, results suggested that I _f was mediated by divalent cation flow through voltage-gated T-type Ca²⁺ channels, whereas I _s was mediated by L- and N-type Ca²⁺ channels in the pulp cell membrane. The expression of these prominent, voltage-gated Ca²⁺ channels in a presumptive mineral-inductive phenotype suggests a functional significance vis a vis differentiation of dental pulp cells for the expression and secretion of matrix proteins, and/or formation of reparative dentin itself. Received: 29 November 1999/Revised: 24 April 2000     

III. Ion Channel Expression in PMA-differentiated Human THP-1 Macrophages

Ion channel expression was studied in THP-1 human monocytic leukemia cells induced to differentiate into macrophage-like cells by exposure to the phorbol ester, phorbol 12-myristate 13-acetate (PMA). Inactivating delayed rectifier K⁺ currents, I _DR, present in almost all undifferentiated THP-1 monocytes, were absent from PMA-differentiated macrophages. Two K⁺ channels were observed in THP-1 cells only after differentiation into macrophages, an inwardly rectifying K⁺ channel (I _IR) and a Ca²⁺-activated maxi-K channel (I _BK). I _IR was a classical inward rectifier, conducting large inward currents negative to E _K and very small outward currents. I _IR was blocked in a voltage-dependent manner by Cs⁺, Na⁺, and Ba²⁺, block increasing with hyperpolarization. Block by Na⁺ and Ba²⁺ was time-dependent, whereas Cs⁺ block was too fast to resolve. Rb⁺ was sparingly permeant. In cell-attached patches with high [K⁺] in the pipette, the single I _IR channel conductance was ∼30 pS and no outward current could be detected. I _BK channels were observed in cell-attached or inside-out patches and in whole-cell configuration. In cell-attached patches the conductance was ∼200–250 pS and at potentials positive to ∼100 mV a negative slope conductance of the unitary current was observed, suggesting block by intracellular Na⁺. I _BK was activated at large positive potentials in cell-attached patches; in inside-out patches the voltage-activation relationship was shifted to more negative potentials by increased [Ca²⁺]. Macroscopic I _BK was blocked by external TEA⁺ with half block at 0.35 mm. THP-1 cells were found to contain mRNA for Kv1.3 and IRK1. Levels of mRNA coding for these K⁺ channels were studied by competitive PCR (polymerase chain reaction), and were found to change upon differentiation in the same direction as did channel expression: IRK1 mRNA increased at least 5-fold, and Kv1.3 mRNA decreased on average 7-fold. Possible functional correlates of the changes in ion channel expression during differentiation of THP-1 cells are discussed. Received: 19 September 1995/Revised: 14 March 1996     

Parameters of a supershort avalanche electron beam generated in atmospheric-pressure air

Conditions under which the number of runaway electrons in atmospheric-pressure air reaches ∼5 × 10¹⁰ are determined. Recommendations for creating runaway electron accelerators are given. Methods for measuring the parameters of a supershort avalanche electron beam and X-ray pulses from gas-filled diodes, as well as the discharge current and gap voltage, are described. A technique for determining the instant of runaway electron generation with respect to the voltage pulse is proposed. It is shown that the reduction in the gap voltage and the decrease in the beam current coincide in time. The mechanism of intense electron beam generation in gas-filled diodes is analyzed. It is confirmed experimentally that, in optimal regimes, the number of electrons generated in atmospheric-pressure air with energies T > eU _m , where U _m is the maximum gap voltage, is relatively small.     

Ni2+ Slows the Activation Kinetics of High-Voltage-Activated Ca2+ Currents in Cortical Neurons: Evidence for a Mechanism of Action Independent of Channel-Pore Block

The effects of Ni²⁺ were evaluated on slowly-decaying, high-voltage-activated (HVA) Ca²⁺ currents expressed by pyramidal neurons acutely dissociated from guinea-pig piriform cortex. Whole-cell, patch-clamp recordings were performed with Ba²⁺ as the charge carrier. Ni²⁺ blocked HVA Ba²⁺ currents (I _Bas) with an EC₅₀ of approximately 60 μm. Additionally, after application of nonsaturating Ni²⁺ concentrations, residual currents activated with substantially slower kinetics than both total and Ni²⁺-sensitive I _Bas. None of the pharmacological components of slowly decaying, HVA currents activated with kinetics significantly different from that of total currents, indicating that the effect of Ni²⁺ on I _Bas kinetics cannot be attributed to the preferential inhibition of a fast-activating component. The effect of Ni²⁺ on I _Ba amplitude was voltage-independent over the potential range normally explored in our experiments (−60 to +20 mV), hence the Ni²⁺-dependent decrease of I _Ba activation rate is not due to a voltage- and time-dependent relief from block. Moreover, Ni²⁺ significantly reduced I _Ba deactivation speed upon repolarization, which also is not compatible with a depolarization-dependent unblocking mechanism. The dependence on Ni²⁺ concentration of the I _Ba activation-rate reduction was remarkably different from that found for I _Ba block, with an EC₅₀ of ∼20 μm and a Hill coefficient of ∼1.73 vs.∼1.10. These results demonstrate that Ni²⁺, besides inhibiting the I _Bas under study probably by exerting a blocking action on the pore of the underlying Ca²⁺ channels, also interferes with Ca²⁺-channel gating kinetics, and strongly suggest that the two effects depend on Ni²⁺ occupancy of binding sites at least partly distinct. Received: 13 July 2000/Revised: 9 November 2000     

Low dose of dopamine may stimulate prolactin secretion by increasing fast potassium currents

Dopamine (DA) released from the hypothalamus tonically inhibits pituitary lactotrophs. DA (at micromolar concentration) opens potassium channels, hyperpolarizing the lactotrophs and thus preventing the calcium influx that triggers prolactin hormone release. Surprisingly, at concentrations ∼1000 lower, DA can stimulate prolactin secretion. Here, we investigated whether an increase in a K⁺ current could mediate this stimulatory effect. We considered the fast K⁺ currents flowing through large-conductance BK channels and through A-type channels. We developed a minimal lactotroph model to investigate the effects of these two currents. Both I _BK and I _A could transform the electrical pattern of activity from spiking to bursting, but through distinct mechanisms. I _BK always increased the intracellular Ca²⁺ concentration, while I _A could either increase or decrease it. Thus, the stimulatory effects of DA could be mediated by a fast K⁺ conductance which converts tonically spiking cells to bursters. In addition, the study illustrates that a heterogeneous distribution of fast K⁺ conductances could cause heterogeneous lactotroph firing patterns. Action Editor: Christiane Linster     

Regulation of Cl− Secretion by Extracellular ATP in Cultured Mouse Endometrial Epithelium

The present study explored regulation of electrogenic ion transport across cultured mouse endometrial epithelium by extracellular ATP using the short-circuit current (I _SC ) and the patch-clamp techniques. The cultured endometrial monolayers responded to apical application of ATP with an increase in I _SC in a concentration-dependent manner (EC₅₀ at 3 μm). Replacement of Cl⁻ in the bathing solution or treatment of the cells with Cl⁻ channel blockers, DIDS and DPC, markedly reduced the I _SC , indicating that a substantial portion of the ATP-activated I _SC was Cl⁻-dependent. Amiloride at a concentration (10 μm) known to block Na⁺ channels was found to have no effect on the ATP-activated I _SC excluding the involvement of Na⁺ absorption. Adenosine was found to have little effect on the I _SC excluding the involvement of P₁ receptors. The effect of UTP, a potent P_2U receptor agonist on the I _SC was similar to that of ATP while potent P_2X agonist, α-β-Methylene adenosine 5′-triphosphate (α-β-M-ATP) and P_2Y agonist, 2-methylthio-adenosine triphosphate (2-M-ATP), were found to be ineffective. The effect of ATP on I _SC was mimicked by the Ca²⁺ ionophore, ionomycin, indicating a role of intracellular Ca²⁺ in mediating the ATP response. Confocal microscopic study also demonstrated a rise in intracellular Ca²⁺ upon stimulation by extracellular ATP. In voltage-clamped endometrial epithelial cells, ATP elicited a whole-cell Cl⁻ current which exhibited outward rectification and delayed activation and inactivation at depolarizing and hyperpolarizing voltages, respectively. The results of the present study demonstrate the presence of a regulatory mechanism involving extracellular ATP and P_2U purinoceptors for endometrial Cl⁻ secretion.     

GISH reveals different levels of meiotic pairing with wheat for individual <Emphasis Type="Italic">Aegilops biuncialis</Emphasis> chromosomes

The Triticum aestivum — Aegilops biuncialis (2n=4x=28; U^bU^bM^bM^b) disomic addition lines 2M^b, 3M^b, 7M^b and 3U^b were crossed with the wheat cv. Chinese Spring ph1b mutant genotype in order to induce homoeologous pairing, with the final goal of introgressing Ae. biuncialis chromatin into cultivated wheat. Wheat-Aegilops homoeologous chromosome pairing was studied in metaphase I of meiosis in the F₁ hybrid lines. Using U and M genomic probes, genomic in situ hybridization (GISH) demonstrated the occurrence of wheat-Aegilops homoeologous pairing in the case of chromosomes 2M^b, 3M^b and 3U^b, but not in the case of 7M^b. The wheat-Aegilops pairing frequency decreased in the following order: 2M^b > 3M^b > 3U^b > 7M^b, which may reflect differences in the wheat-Aegilops homoeologous relationships between the examined Aegilops chromosomes. The selection of wheat-Aegilops homoeologous recombinations could be successful in later generations.     

Partial purification and characterization of an ascorbate-reducible b-type cytochrome from the plasma membrane of Arabidopsis thaliana leaves

Summary.  The plant plasma membrane (PM) contains more than one b-type cytochrome. One of these proteins has a rather high redox potential (can be fully reduced by ascorbate) and is capable of transporting electrons through the PM. Four genes encoding proteins with considerable homology to the sequences of cytochrome b ₅₆₁ proteins in the animal chromaffin granule membrane have recently been identified in the genome of Arabidopsis thaliana. In order to characterize the cytochrome b ₅₆₁ located in the Arabidopsis PM, first PM vesicles were purified by aqueous polymer two-phase partitioning from the leaves of 9-week-old A. thaliana. PM proteins were solubilized by nonionic detergent, and the fully ascorbate-reducible b-type cytochrome was partially purified by anion-exchange chromatography steps. Potentiometric redox titration of the fraction, containing the fully ascorbate-reducible b-type cytochrome after the first anion-exchange chromatography step, revealed the presence of two hemes with redox potentials of 135 mV and 180 mV, respectively. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the fractions containing the fully ascorbate-reducible b-type cytochrome after the second anion-exchange chromatography step revealed the presence of a single polypeptide band at about 120 kDa. However, heat treatment (15 min, 90 °C) before electrophoresis was able to split the 120 kDa band into two bands with molecular masses of about 23 and 28 kDa. These values are lower than the apparent molecular mass for the fully ascorbate-reducible b-type cytochrome purified from Phaseolus vulgaris hypocotyls (about 52 kDa) but are in good agreement with those characteristic for the cytochrome b ₅₆₁ proteins purified from chromaffin granule membranes (about 28 kDa) and the four polypeptides predicted from the Arabidopsis genome (24–31 kDa). Received May 4, 2002; accepted July 26, 2002; published online May 21, 2003 RID="*" ID="*" Correspondence and reprints: Institute of Biophysics, BRC, Hungarian Academy of Sciences, POB 521, 6701 Szeged, Hungary.