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Dynamic plasma pinches occur in a variety of devices, as Z-pinches and plasma focus. In this paper, a lumped parameter model of a dynamic plasma pinch produced in a plasma focus discharge is presented. The model is based in Von Karman approximations of the radial density and velocity profiles, which leads to the reduction to a system of ordinary differential equations describing the dynamic evolution of the pinch compression and expansion. The model was coupled with a fusion kernel to produce an estimate of the neutron yield per pulse. The calculations were tested against available data of the pressure–yield curve of seven experimental devices ranging from 1 to 250 kJ, showing excellent agreement, particularly regarding the curvature of the pressure–yield curve. Fil: Gonzalez, Jose Hector. Comision Nacional de Energia Atomica. Gerencia D/area Invest y Aplicaciones No Nucleares. Gerencia Proyecto Lasie.; Argentina Fil: Brollo, Fabricio Raul. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina Fil: Clausse, Alejandro. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Grupo de Plasmas Densos Magnetizados. Provincia de Buenos Aires. Gobernación. Comision de Investigaciones Científicas. Grupo de Plasmas Densos Magnetizados; Argentina

La región de cultivo de girasol en la Argentina presenta una fuerte variabilidad ambiental, tanto estacional como espacial. En consecuencia, las combinaciones sitio-año en que se establecen ensayos comparativos de rendimiento pueden complicar la elección de híbridos de girasol a través de fuertes interacciones genotipo × ambiente (G×E). El objetivo de este trabajo es establecer criterios que mejoren la respuesta a la selección de híbridos de girasol en ensayos oficiales. Para ello se analizó un conjunto de ensayos correspondientes a la RNG del INTA. Se estimaron los componentes de varianza, se compararon estrategias de selección en función de la heredabilidad en sentido amplio y se aplicaron análisis de patrones sobre matrices de genotipos × ambientes. Para rendimiento de aceite, la interacción G×E explicó 3.46 veces más variabilidad que el efecto genotípico. Con pocos años y localidades se alcanzan bajos valores de heredabilidad, lo que resulta en falta de certeza en las decisiones de selección. Un adecuado muestreo de la región girasolera se lograría más eficientemente aumentando el número de localidades en lugar del número de años de evaluación. Si el objetivo de una estrategia de evaluación fuera trabajar con una heredabilidad promedio superior al 80%, deberían conducirse ensayos durante más de 4 años y en más de 14 localidades. El análisis de clasificación reveló 4 grupos genotípicos de respuestas relativas variables a lo largo de 3 grupos ambientales y confirmó la necesidad de un adecuado muestreo de la región girasolera para evitar seleccionar genotipos de respuesta impredecible. El análisis de componentes principales confirmó observaciones previas acerca de considerar a las regiones central y norte como diferentes megaambientes para el cultivo de girasol.

Alfalfa plants grown in soil at different growth stages were exposed to separate batches of Cr(VI) at 100 mg/l, and Cd(II), Cu(II), Ni(II), or Zn(II) at 500 mg/l. Four days after germination, all metals, except Zn(II), had lethal effects on the alfalfa seedlings. Furthermore, when applied 16 days after germination, Cr(VI) and Ni(II) still had lethal effects on the seedlings and Cd(II) and Cu(II) destroyed more than 50% of the plant population. While approximately 90% of the plants exposed to Cd(II), Cu(II) and Zn(II) were able to grow without apparent negative effects 20 days after germination, Cr(VI) and Ni(II) still showed lethal effects. The concentration of heavy metals in shoot dry tissues was 1209 mg/kg for Cd, 887 mg/kg for Cu and 645 mg/kg for Zn. These results demonstrated that the tolerance of alfalfa plants to Cd, Cu and Zn was positively correlated with the age of the plants. Also, these results opened the possibility of using alfalfa plants, via transplant, to clean up soils where the concentration of Cd, Cu or Zn is high enough to avoid alfalfa seed germination.

Europium(III) is a common product found in nuclear wastes. Recent investigations into the use of europium compounds as cancer therapy treatments have proven promising. In this study, europium(III) nitrate binding studies were performed using unmodified and esterified alfalfa biomass. Batch experiments included pH profile studies and X-ray absorption spectroscopy (XAS) inspection to determine the functional groups responsible for the binding of europium(III) nitrate on alfalfa. Results from the pH profile study showed that approximately 80% of the europium(III) nitrate bound to the native alfalfa biomass while the esterified biomass showed approximately 40% binding at pH 5. XAS consists of two complementary components: X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The XAS experiments were performed using the europium LIII edge which had an energy of 6.977 KeV. The XANES spectra showed that there were some changes in the characteristics of the europium(III) nitrate when bound to the modified and unmodified alfalfa biomass. No change in the europium(III) oxidation state was observed after europium(III) binding to the alfalfa biomass. EXAFS spectra showed that europium(III) nitrate binds to the alfalfa biomass via a nitrogen or oxygen ligand with bond lengths ranging from 2.44 to 2.49 A. However, chemical esterification experiments show that oxygen may be the primary ligand for coordination. The coordination numbers for all samples and compounds tested were approximately 9.

Previous laboratory batch experiments of Medicago sativa (Alfalfa) indicated that the African shoots population had an appreciable ability to bind copper(II) and nickel(II) ions from aqueous solution. Batch laboratory pH profile, time dependency and capacity experiments were performed to determine the binding ability of the African shoots for cadmium(II), chromium(III), chromium(VI), lead(II), and zinc(II). Batch pH profile experiments for the mentioned ions indicated that the optimum pH for metal binding is approximately 5.0. Time dependency experiments for all the metals studied showed that metal binding to the African alfalfa shoots occurred within 5 min. Binding capacity experiments revealed the following amounts of metal ions bound per gram of biomass: 7.1 mg Cd(II), 7.7 mg Cr(III), 43 mg Pb(II), and 4.9 mg Zn(II). However, no binding occurred for chromium(VI). Nearly all of the metals studied were recoverable by treatment with 0.1 M HCl. Column experiments were performed to study the binding of Cd(II), Cr(III), Cr(VI), Pb(II) and Zn(II) to silica-immobilized African alfalfa shoots under flow conditions. These experiments showed that the silica immobilized African alfalfa shoots were effective for removing metal ions from solution, and over 90% of the bound Pb(II), Cu(II), Ni(II), and Zn(II), and over 70%Cd(II), were recovered after treatment with 10 bed volumes of 0.1 M HCl. The results from these studies will be useful for a novel phytofiltration technology to remove and recover heavy metal ions from aqueous solution.

Previous batch laboratory experiments performed to determine the potential ability of seven different varieties of Medicago sativa (Alfalfa, African variety) revealed that the shoots tissue-derived population was able to efficiently bind copper(II) and nickel(II) from aqueous solutions. Batch laboratory interference studies were performed with various calcium and magnesium concentrations (0.1 mM–1 M) in order to ascertain the effects of these ions on the heavy metal binding ability of African alfalfa shoots. Results from these studies have shown that calcium and magnesium did not seriously reduce the binding of copper(II), lead(II), to African alfalfa shoot tissues. However, high concentrations of calcium and magnesium, to some extent, reduced chromium(III), cadmium(II), nickel(II), and zinc(II) binding to African shoot tissues. In addition, all these experiments were repeated maintaining constant ionic strength, and similar results were obtained. Interference studies were also conducted in order to determine the effects of hard cations under flow conditions with silica immobilized African alfalfa shoots. Column experiments under flow conditions produced similar results than batch laboratory experiments. The information obtained from these studies will be useful for an innovative method to remove and recover heavy metal ions from contaminated waters.

Agronomic efficiency (kg grain yield kg−1 N applied) is conditioned by environmental factors and nitrogen availability during the growing period. Hence, a fertilization model that considers environmental factors affecting wheat crop growth and effective N supply should be based on crop N demand. In this work, a simple model based on N balance during the growing season is used as the frame to simulate both the demand and the availability of N, and to determine grain yield. Fertilization experiments were conducted under different environments (50 sites, 8 y) of the Southern Pampa of Argentina. Nitrogen fertilization rates ranged between 25 and 125 kg N ha−1. Soil initial conditions and water balance during the crop cycle were found to modify both N demand and soil N supply. The amount of N taken up by crops, water balance during the crop growth period and mean maximum temperature during grain filling, all affected grain yield components. The proposed model provided a good agreement between observed independent data sets and simulated values of grain yield (root mean square error = 9% of the mean value). Model operation was performed for one site within the region using climatic records to estimate annual grain yield variability under three levels of N availability.

The characteristics of the roots and shoots from seven different populations of Medicago sativa (alfalfa) were examined for their ability to bind nickel ions from aqueous solution. Batch laboratory experiments were performed to determine the optimal pH for nickel binding to the alfalfa plant tissues which was between pH 5 and 6. From these experiments, pH profiles were performed to gain information about the chemical functional groups in the alfalfa plant tissues responsible for the nickel binding. Binding time dependency studies determined that approximately 80% of the nickel ions bound to the alfalfa plant tissues in less than 5 min. Binding capacity experiments showed that nickel binding was as much as 4.1 mg of nickel per gram of alfalfa biomass. Nickel recovery experiments showed that more than 90% of the bound nickel was removed from the alfalfa biomass. Column experiments were conducted to examine the binding of nickel to silica immobilized alfalfa plant tissues under flow conditions. Results from these experiments showed that more than 90% of the retained nickel was recovered after four bed volumes of 0.1 M HC1 solution were passed through the column. After 12 cycles on the same column, the efficiency for nickel removal and recovery from solution was stable.

Preliminary screening laboratory batch experiments to determine the binding ability of seven different populations of Medicago sativa (alfalfa) showed good copper binding characteristics of the biomasses studied. All seven populations examined had similar trends for binding copper as a function of pH. The copper binding by the different alfalfa populations occurred within 5 min. All the alfalfa biomasses showed high copper binding, but the capacities varied according to the alfalfa sample studied. The pH dependence of the copper ion binding to the alfalfa biomasses suggested that it might be possible to recycle the system much like an ion-exchange resin. However, the alfalfa cells cannot be packed into a column because the cells clump together and restrict the flow. We immobilized the cells of Malone alfalfa shoots in a silica matrix. Column experiments for copper binding by the silica immobilized alfalfa demonstrated that the alfalfa tissues were capable of removing considerable amounts of copper ions under flow conditions. After every copper binding cycle most of the copper was desorbed with a few bed volumes of 0.1 M HCl. Our work indicates that the Malone-silica preparations are highly durable. We subjected the biomaterial to as many as 10 cycles of binding and elution without observing any significant decrease in copper binding capacity.

Seven different varieties of alfalfa plant tissues were tested for their ability to uptake copper ions from solution. Laboratory experiments were performed to determine the pH profiles, time dependency, capacity of copper uptake and desorption of the metal bound. Also, optimal biomass drying conditions (oven dried and lyophilized) as well as buffering effects on the copper uptake were examined. Differences in the roots and shoots were examined to determine the metal binding properties of seven alfalfa populations. Protein and crude fiber content was determined for all biomasses studied. Most of the biomasses studied showed a high affinity for copper ions as the pH increased from 2 to 6 with optimum copper binding around pH 5.0. Time dependency experiments for copper binding showed a very rapid adsorption of the copper ions by the various alfalfa species. Binding capacity experiments for copper binding showed that the capacities of the shoots are very similar, with African and Ladak germplasms bei...

Experimental results have shown that the desert plant species mesquite (Prosopis spp.) is capable of accumulating high levels of lead in the roots, translocating it to the aerial portion of the plant. One-week-old mesquite seedlings were treated for 7 d in a hydroponic culture using a modified Hoagland solution. Six treatments were used; three treatments contained only Pb [as Pb(NO3)2] at 25-, 50-, and 75-mg L(-1) levels and three treatments contained the same levels of Pb, but with equimolar concentrations of disodium ethylenediamine tetraacetic acid (EDTA). Our results showed that the plants exposed to 25-, 50-, and 75-mg Pb L(-1) treatments without EDTA concentrated in stems 524, 3726, and 1417 mg kg(-1), respectively. However, the plants treated with Pb-EDTA concentrated in stems 480-, 607-, and 1247-mg Pb kg(-1) for the 25-, 50-, and 75-mg Pb L(-1) treatments, respectively. Results for the roots followed a similar trend; without EDTA the Pb levels ranged from 16,055, 89,935, and 63,396 for the 25-, 50-, and 75-mg Pb L(-1) treatments, respectively, and with EDTA these levels were 9,562, 49,902, and 39,181 mg kg(-1) for the three treatments. However, the addition of EDTA increased lead movement to the leaves. The levels of Pb without EDTA were 20, 35, and 51 mg kg(-1) for the 25-, 50-, and 75-mg Pb L(-1) levels, respectively. Treatments with EDTA showed uptake levels of 105, 124, and 313 for the 25-, 50-, and 75-mg Pb L(-1) treatments. Further, the percent Pb in dry leaf tissues for all EDTA treatments were greater than 0.1%. However, only the 25-mg Pb L(-1) treatment was greater than 0.1%, compared to 0.04 and 0.08% for the 50- and 75-mg Pb L(-1) treatments, respectively. Preliminary transmission and scanning electron microscopy corroborate the presence of lead.

The effect of pH on Cd(II) binding capacity of saltbush biomass was determined. Metal quantification performed using ICP/OES showed that Cd binding increased as pH increased from 2.0 to 5.0. The highest percentage of Cd bound ranged from 74-81%, 22-40%, and 70-80% for the native, esterified, and hydrolysed biomass. XAS studies showed that cadmium was present as Cd(II) and oxygen was the nearest neighbouring atom with bond lengths of approximately 2.3 A and coordination numbers ranging between 4 and 5. Results indicated that carboxyl groups may be the primary ligand involved in the Cd binding by saltbush biomass.

The formation and reduction of anodic films on Os electrodes in 2 M HCl and HClO4 solutions were studied by anodic and cathodic charging curves. The galvanostatic oxidation of Os in HClO4 shows the formation of OsO2 as an intermediate step to OsO4 that goes in the solution. The cathodic charging curves at Os electrodes previously oxidized at constant potential reveal the anodic film to be made up of a reversibly desorbed oxygen layer and an oxide phase reduced irreversibly. Both layers increase with time under potentiostatic conditions following a logarithmic equation until a constant value is reached. At all times, the content of OsO2 in the anodic film at high potentials is larger than that of chemisorbed oxygen. In HCl solutions only the reversible reduction of an oxygen layer is observed. The growth of this film also complies with a direct logarithmic law before attaining a limiting coverage. The charge involved in the reduction increases linearly with the potential at a given time of formation. The results are discussed in terms of a Temkin-type isotherm and a place-exchange mechanism.

Anodic film formation and reduction on electrodeposited Os was studied in strong HCl and HClO4 solutions. Significant voltammograms were obtained only after long pre-reduction of the electrode and at slow potential sweeps. The potentiodynamic curves reveal strong adsorption of oxygen with formation of OsO2 and further oxidation to OsO4 which goes into solution. In strong HCl solutions a corrosion step at high potential with formation of OsO2Cl42− is detected. The influence of scan rate on peak potential and current and the charge capacity of the electrode surface was investigated. Anion adsorption and increase in acid concentration was found to reduce the extent of the anodic film. The results are discussed in terms of the formation of thick surface oxides and compared with those for Ir and Ru.

The anodic dissolution of Os in acidic solutions was studied under potentiostatic conditions. The results show high dissolution rates that increase markedly at rising potential. The presence of chloride ions and to a greater extent the increase in acidity of the solutions inhibit the anodic corrosion process. The nature of the dissolution products did depend on the solution pH and the concentration of the complexing anion. Thus, in HClO 4 acid and in chloride solutions at low concentration or acidity, Os goes into solution as OsO 4 ; in concentrated HCl solution, tetraoxide and chloro-osmyl anions are formed. No OsCl 6 2− complex was detected in solution even at high HCl concentration.