Nutrient uptake relationship to root characteristics of rice

Data on root parameters and distribution are important for an improved understanding of the factors influencing nutrient uptake by a crop. Therefore, a study was conducted on a Crowley silt loam at the Rice Research and Extension Center near Stuttgart, Arkansas to measure root growth and N, P and K uptake by three rice (Oryza sativa L.) cultivars at active tillering (36 days after emergence (DAE)), maximum tillering (41 DAE), 1.25 cm internode elongation (55 DAE), booting (77 DAE) and heading (88 DAE). Soil-root core samples were taken to a depth of 40 cm after plant samples were removed, sectioned into 5 cm intervals, roots were washed from soil and root lengths, dry weights and radii were measured. Root parameters were significantly affected by the soil depth × growth stage interaction. In addition, only root radius was affected by cultivar. At the 0- to 5-cm soil depth, root length density ranged from 38 to 93 cm cm^-3 throughout the growing season and decreased with depth to about 2 cm cm^-3 in the 35- to 40-cm depth increment. The increase in root length measured with each succeeding growth stage in each soil horizon also resulted in increased root surface area, hence providing more exposed area for nutrient uptake. About 90% of the total root length was found in the 0- to 20-cm soil depth throughout the season. Average root radius measured in the 0- to 5-cm and 35- to 40-cm depth increments ranged from 0.012 to 0.013 cm and 0.004 to 0.005 cm, respectively throughout the season. Total nutrient uptake by rice differed among cultivars only during vegetative growth. Differences in total nutrient uptake among the cultivars in the field appear to be related to absorption kinetics of the cultivars measured in a growth chamber study. Published with permission of the Arkansas Agricultural Experiment Station.     

Studies of the structure of C pellet ablation clouds in W7-AS

The structure of the ablation clouds surrounding carbon pellets injected into the ECR-heated Wendelstein 7-AS plasma has been studied. Snapshot and integrated photographs obtained in the spectral ranges containing the CII (720 ± 5 nm and 723 ± 1 nm) and CIII (770 ± 5 nm) spectral lines were analyzed over a wide range of the bulk plasma parameters. It is found that the cloud luminosity profile along the magnetic field is exponential with either one or two characteristic decay lengths of about a few millimeters and a few centimeters. The smaller length corresponds to the zone closer to the pellet. There is good agreement between the characteristic decay lengths deduced from snapshot and integrated photographs. The characteristic decay lengths were obtained along the entire pellet trajectory and were found to change weakly in the central region and to grow at the plasma periphery (generally, in inverse proportion to the plasma electron density). In the central region, the characteristic decay lengths are about a few millimeters and 1 cm. They depend weakly on the bulk plasma temperature and decrease with increasing bulk plasma density. These lengths agree fairly well with estimates of the ionization length of carbon ions into the C²⁺, C³⁺, and C⁴⁺ charge states, respectively, assuming that ionization is provided by the hot electrons of the bulk plasma and that the cloud expands with the ion-acoustic velocity at a temperature of ～1 eV. The results obtained prove that the cloud structure in the vicinity of the pellet is mainly determined by the bulk plasma electrons.     

Diagnostics of soft X-ray emission from the plasma of a fast capillary discharge

Results are presented from time-resolved measurements of the soft X-ray emission in the 10-to 40-eV spectral range from the plasma of a pulsed capillary discharge in argon at current pulse amplitudes of up to 26 kA and a current rise time of ～10¹² A/s. The experiments were carried out with 0.3-cm-diameter 15.7-cm-long ceramic capillaries filled with argon at a pressure of 0.25–0.5 Torr in the SIGNAL electrophysical facility. The experimental data are interpreted via computer simulations of the magnetohydrodynamics and level-by-level ion kinetics of an argon plasma. The results obtained indicate that soft X-ray laser pulses with a photon energy of 26.4 eV and duration of 1–2 ns are generated ≈33 ns after the beginning of the discharge current pulse.     

Diagnostics of MHD instability in the Globus-M spherical tokamak

The paper describes a diagnostic system for studying MHD plasma perturbations in the Globus-M spherical tokamak (a major radius of 0.36 m, a minor radius of 0.24 m, and an aspect ratio of 1.5). The system includes a poloidal and a toroidal array consisting of 28 and 16 Mirnov probes, respectively, as well as a 32-channel proportional soft X-ray detector. Methods are described for calculating the poloidal and toroidal numbers of the dominant helical perturbations by using data from probe measurements. Results are presented of processing the experimental data from some tokamak discharges with a plasma current of 150–250 kA, an average electron density of up to 10²⁰ m^?3, and a toroidal magnetic field of 0.4 T. Specific features of MHD perturbations and their influence on the parameters of the plasma column in different stages of a discharge are briefly discussed.     

Investigation of the electron energy distribution function in hollow-cathode glow discharges in nitrogen and oxygen

The mechanism for the formation of the inverse electron distribution function is proposed and realized experimentally in a nitrogen plasma of a hollow-cathode glow discharge. It is shown theoretically and experimentally that, for a broad range of the parameters of an N₂ discharge, it is possible to form a significant dip in the profile of the electron distribution function in the energy range ε=2–4 eV and, accordingly, to produce the inverse distribution with df(ε)/d?>0. The formation of a dip is associated with both the vibrational excitation of N₂ molecules and the characteristic features of a hollow-cathode glow discharge. In such a discharge, the applied voltage drops preferentially across a narrow cathode sheath. In the main discharge region, the electric field E is weak (E<0.1 V/cm at a pressure of about p～0.1 torr) and does not heat the discharge plasma. The gas is ionized and the ionization-produced electrons are heated by a beam of fast electrons (with an energy of about 400 eV) emitted from the cathode. A high-energy electron beam plays an important role in the formation of a dip in the profile of the electron distribution function in the energy range in which the cross section for the vibrational excitation of nitrogen molecules is maximum. A plasma with an inverted electron distribution function can be used to create a population inversion in which more impurity molecules and atoms will exist in electronically excited states.     

Study of the plasma parameters in a high-current pulsed magnetron sputtering system

Results are presented from experimental studies of the current-voltage characteristics and spatial and temporal parameters of the plasma in a high-current pulsed magnetron sputtering system with a 10-cm-diameter plane disk cathode. It is shown that the plasma density in such a system is three orders of magnitude higher than that in conventional dc magnetron discharges and reaches 10¹³ cm⁻³ at a distance of 250 mm from the cathode at a peak discharge current of 500 A. The plasma propagates from the cathode region at a velocity of 1 cm/μs in the axial direction and 0.25 cm/μs in the radial direction. Optical emission spectroscopy shows that the degree of plasma ionization increases severalfold with increasing discharge current, mainly at the expense of the sputtered material.     

Numerical simulations of spark channels propagating along the ground surface: Comparison with high-current experiment

A numerical model of a spark discharge propagating along the ground surface from the point at which an ∼100-kA current pulse is input into the ground has been developed based on experiments in which the velocity of a long leader was measured as a function of the leader current. The results of numerical simulations are in good agreement with the measured characteristics of creeping discharges excited in field experiments by using a high-power explosive magnetic generator. The reason why the length of a spark discharge depends weakly on the number of simultaneously developing channels is found. Analysis of the influence of the temporal characteristics of the current pulse on the parameters of the creeping spark discharge shows that actual lighting may exhibit similar behavior.     

Capillary discharges for guiding of laser pulses

The dynamics of a capillary discharge is studied to achieve optimum conditions for the guiding of ultrashort intense laser pulses. A dynamic regime is revealed in which, after a short transient process, the discharge plasma is in dynamic and thermal equilibrium. Such plasma configuration is stable against MHD perturbations. It is shown that the radial inhomogeneity of the discharge plasma composition can provide the improvement of the focusing properties of a plasma waveguide. The radius of the region where electromagnetic radiation is localized is governed by a contact discontinuity between the plasma that initially fills the channel and the plasma that is produced due to ablation of the capillary wall material.     

Generation of uniform low-temperature plasma in a pulsed non-self-sustained glow discharge with a large-area hollow cathode

Generation of plasma in a pulsed non-self-sustained glow discharge with a hollow cathode with an area of ≥2 m² at gas pressures of 0.4–1 Pa was studied experimentally. At an auxiliary arc-discharge current of 100 A and a main discharge voltage of 240 V, a pulse-periodic glow discharge with a current amplitude of 370 A, pulse duration of 340 μs, and repetition rate of 1 kHz was obtained. The possibility of creating a uniform gas-discharge plasma with a density of up to 10¹² cm^?3 and an electron temperature of 1 eV in a volume of >0.2 m³ was demonstrated. Such plasma can be efficiently used to treat material surfaces and generate pulsed ion beams with a current density of up to 15 mA/cm².     

Experimental investigation of the shock wave in a fast discharge with cylindrical geometry

The work is devoted to the registration and the study of the properties of cylindrical shock waves generated in the fast discharge (dI/dt ～ 10¹² A/s) inside the ceramic tube (Al₂O₃) filled by argon at pressures of 100 and 300 Pa. The shock wave appears at the inner wall of the insulator and moves to the discharge axis with a velocity of about (3?4) × 10⁶ cm/s with subsequent cumulation. The plasma behind the front is heated enough to produce radiation in the vacuum ultraviolet (VUV) region, which makes it possible to study its structure by means of a pinhole camera with a microchannel plate detector. The time resolution of the registration system was 10 ns. The analysis of VUV spectra of the plasma shows that the electron temperature behind the shock wave front is about several eV; after the moment of cumulation, its temperature increases to 20–30 eV.     

Determination of the electron density and electric field in the plasma of a low-pressure microwave electrode discharge in hydrogen from the measured spectral line intensities

The parameters of the plasma of a microwave electrode discharge in hydrogen at pressures of 1–8 torr and incident powers of 20–80 W are measured by the so-called “relative intensity” method. The method allows one to determine the electron density and electric field in plasma by measuring the relative intensities of the H_α, H_β, and 763.5-nm Ar line emission and calculating the electron-impact rate constants from the homogeneous Boltzmann equation. The measurements show that there are regions in the discharge where the electron density is higher (a bright electrode sheath) and lower (a spherical region) than the critical density for the frequency 2.45 GHz (n_cr～7×10¹⁰ cm^?3). Inside the spherical region, the electric field varies slightly over the radius and the electron density increases as the discharge boundary is approached. The observed discharge structure can be attributed to the presence of a self-sustained discharge zone (electrode sheath); a non-self-sustained discharge zone (spherical region); and a decaying plasma region, which is separated from the active discharge zone by an electric double layer.     

Metabolism,Gas Exchange,and Carbon Spiraling in Rivers

Ecosystem metabolism, that is, gross primary productivity (GPP) and ecosystem respiration (ER), controls organic carbon (OC) cycling in stream and river networks and is expected to vary predictably with network position. However, estimates of metabolism in small streams outnumber those from rivers such that there are limited empirical data comparing metabolism across a range of stream and river sizes. We measured metabolism in 14 rivers (discharge range 14–84 m³ s^?1) in the Western and Midwestern United States (US). We estimated GPP, ER, and gas exchange rates using a Lagrangian, 2-station oxygen model solved in a Bayesian framework. GPP ranged from 0.6–22 g O₂ m^?2 d^?1 and ER tracked GPP, suggesting that autotrophic production supports much of riverine ER in summer. Net ecosystem production, the balance between GPP and ER was 0 or greater in 4 rivers showing autotrophy on that day. River velocity and slope predicted gas exchange estimates from these 14 rivers in agreement with empirical models. Carbon turnover lengths (that is, the distance traveled before OC is mineralized to CO₂) ranged from 38 to 1190 km, with the longest turnover lengths in high-sediment, arid-land rivers. We also compared estimated turnover lengths with the relative length of the river segment between major tributaries or lakes; the mean ratio of carbon turnover length to river length was 1.6, demonstrating that rivers can mineralize much of the OC load along their length at baseflow. Carbon mineralization velocities ranged from 0.05 to 0.81 m d^?1, and were not different than measurements from small streams. Given high GPP relative to ER, combined with generally short OC spiraling lengths, rivers can be highly reactive with regard to OC cycling.     

Plasma creatinine and creatine quantification by capillary electrophoresis diode array detector

Traditional clinical assays for nonprotein nitrogen compounds, such as creatine and creatinine, have focused on the use of enzymes or chemical reactions that allow measurement of each analyte separately. Most of these assays are mainly directed to urine quantification, so that their applicability on plasma samples is frequently hard to perform. This work describes a simple free zone capillary electrophoresis method for the simultaneous measurement of creatinine and creatine in human plasma. The effect of analytical parameters such as concentration and pH of Tris-phosphate running buffer and cartridge temperature on resolution, migration times, peak areas, and efficiency was investigated. Good separation was achieved using a 60.2-cm x 75-microm uncoated silica capillary, 75 mmol/L Tris-phosphate buffer, pH 2.25, at 15 degrees C, in less than 8 min. We compared the present method to a validated capillary electrophoresis assay, by measuring plasma creatinine in 120 normal subjects. The obtained data were compared by the Passing-Bablok regression and the Bland-Altman test. Moreover the performance of the developed method was assessed by measuring creatine and creatinine in 16 volunteers prior to and after a moderate physical exercise.     

Microwave Electromagnetic Field Affects the Corona Discharge Pattern of Water

We investigated the influence of microwave irradiation (cw; 10 GHz) on water by means of corona discharge electrography. Water drops from previously irradiated and control water were exposed to a high-voltage, high-frequency electric field on a photographic plate. Electrographs of the corona discharge around control and irradiated drops were taken simultaneously, and the images obtained were analyzed by computer. Several parameters relating to the luminosity, shape, and streamers of the image were calculated and tested nonparametrically. The results show a distinct, nonlinear behavior of corona discharge patterns (both radially and angularly) in water drops exposed to different microwave power densities (5 × 10^?1-5 × 10^?8 mWcm^?2).     

Hydrodynamic model of a dielectric-barrier discharge in pure chlorine

A one-dimensional hydrodynamic model of a dielectric-barrier discharge (DBD) in pure chlorine is developed, and the properties of the discharge are modeled. The discharge is excited in an 8-mm-long discharge gap between 2-mm-thick dielectric quartz layers covering metal electrodes. The DBD spatiotemporal characteristics at gas pressures of 15–100 Torr are modeled for the case in which a 100-kHz harmonic voltage with an amplitude of 8 kV is applied to the electrodes. The average power density deposited in the discharge over one voltage period is 2.5–5.8 W/cm³. It is shown that ions and electrons absorb about 95 and 5% of the discharge power, respectively. In this case, from 67 to 97% of the power absorbed by electrons is spent on the dissociation and ionization of Cl₂ molecules. Two phases can be distinguished in the discharge dynamics: the active (multispike) phase, which follows the breakdown of the discharge gap, and the passive phase. The active phase is characterized by the presence of multiple current spikes, a relatively high current, small surface charge density on the dielectrics, and large voltage drop across the discharge gap. The passive phase (with no current spikes) is characterized by a low current, large surface charge density on the dielectrics, and small voltage drop across the discharge gap. The peak current density in the spikes at all pressures is about 4 mA/cm². In the multispike phase, there are distinct space charge sheaths with thicknesses of 1.5–1.8 mm and a mean electron energy of 4.3–7 eV and the central region of quasineutral plasma with a weak electric field and a mean electron energy of 0.8–3 eV. The degree of ionization of chlorine molecules in the discharge is ~0.02% at a pressure of 15 Torr and ~0.01% at 100 Torr. The DBD plasma is electronegative due to the fast attachment of electrons to chlorine atoms: e + Cl₂ → Cl + Cl^–. The most abundant charged particles are Cl ₂ ⁺ and Cl^? ions, and the degree of ionization during current spikes in the active phase is (4.1–5.5) × 10^–7. The mechanism of discharge sustainment is analyzed. The appearance of a series of current spikes in the active phase of the discharge is explained.     

Experiments with small-size dynamic loads in the S-300 high-power pulsed generator

Results are presented from experimental studies of promising output units for high-current pulsed generators within the framework of the program on inertial confinement fusion research with the use of fast Z-pinches. The experiments were carried out on the S-300 facility (4 MA, 70 ns, 0.15 Ω). Specifically, sharpening systems similar to plasma flow switches but operating in a nanosecond range were investigated. Switching rates to a load as high as 2.5 MA per 2.5 ns, stable switching of a 750-kA current to a low-size Z-pinch, and the radiative temperature of the load cavity wall of up to 50 eV were achieved.     

Ionization fraction of the sputtered metal flux in a hollow cathode magnetron

Results from studies of the parameters of a novel type of plasma source—a hollow cathode magnetron—are presented. The magnetron operates at a gas pressure of 5–20 mTorr, the discharge power being in the range of 0.5–4 kW. At discharge powers exceeding 2 kW, a plasma flow with a density of higher than 10¹¹ cm^?3 and length of up to 30 cm forms at the magnetron output. Using a grid quartz crystal microbalance, the ionized copper flux fraction was measured as a function of the gas pressure, discharge power, and distance from the target. At gas pressures of higher than 15 mTorr, the degree of ionization at a distance of 31 cm exceeds 50%.     

Plasma electron-emitting source in a low-pressure beam-plasma discharge in a stationary plasma thruster

A new type of plasma electron-emitting source capable of increasing the temperature of plasma electrons behind the edge of a stationary plasma thruster (SPT) to 7–15 eV has been developed and investigated experimentally. For the same parameters of the main discharge, the thrust, the thrust efficiency, the mass use factor, and the lifetime of the “SPT anode unit-plasma electron-emitting source” assembly are found to increase substantially as compared to a thruster equipped with a conventional cathode compensator. Simultaneously, the neutral particle pressure required for the existence of self-consistent distributions of the electric field and charged particle density in the drift space of the neutralized ion beam decreases appreciably. It is shown that the volume of the region in which primary slow ions are produced increases with increasing ionization frequency. Three additional channels for discharge control are implemented. The ranges in which the discharge parameters can be controlled are extended.     

Plasma and ion beam injection into an FRC

Experiments on the transverse injection of intense (5–20 A/cm²), wide cross-section (10-cm), neutralized, ～100-eV H⁺ plasma and 100-keV H⁺ ion beams into a preformed B-field reversed configuration (FRC) are described. The FRC background plasma temperature was ～5 eV with densities of ～10¹³ cm^?3. In contrast to earlier experiments, the background plasma was generated by separate plasma gun arrays. For the startup of the FRC, a betatron-type “slow” coaxial source was used. Injection of the plasma beam into the preformed FRC resulted in a 30–40% increase of the FRC lifetime and the amplitude of the reversed magnetic field. As for the ion beam injection experiment into the preformed FRC, there was evidence of beam capture within the configuration.     

Double layer in a cylindrical hollow-cathode discharge

A dc cylindrical coaxial glow discharge with an inner grid anode has been studied. The region between the two electrodes is seen dark, while a brightly glowing region forms inside the grid anode up to the center. The current-voltage characteristic of a dc cylindrical glow discharge in nitrogen is similar to that of a normal glow discharge, while the normal glow discharge voltage decreases with increasing pressure. The minimum plasma potentials are observed in the hollow cathode region due to the accumulation of electrons at the back of the grid anode. At the center, some of the passed electrons are converged, so their potential is decreased. These electrons have a sufficient time to be redistributed to form one group with a Maxwellian electron energy distribution function. The electron temperature measured by electric probes varies from 1.6 to 3.6 eV, while the plasma density varies from 3.9 × 10¹⁶ to 7 × 10¹³ m⁻³, depending on the discharge current and probe position. The plasma density increases as the electrons move radially from the grid toward the central region, while their temperature decreases.