Electron sources for plasma electronics and different technological application

There are the following advantages of applying electron guns with plasma cathodes in devices exciting microwave radiation: stability of their parameters, high density of current, relative insensitivity to ion bombardment and the possibility of operating over a wide range of pressure values of a plasma-generating gas [1-5]. The given work aims at constructing the guns with the parameters necessary for the excitation of microwaves of high amplitudes in the slow-wave structures: the beam energy is 20-30 kV, the current is up to 5 A, and the pulse duration is 0,11÷1 ms. The principal problem arising during construction of heavy-current electron sources with plasma emitters consists in the following: it is necessary to provide such conditions of the gas volume, under which the discharge firing would be stable and the emissive plasma generation be effective, whereas a gas breakdown in the accelerating gap must be eliminated

Compositional, spectroscopic and rheological analyses of mucilage isolated from taro (Colocasia esculenta L. Schott) corms

Please help us populate SUNScholar with the post print version of this article. It can be e-mailed to: [email protected]

Profiling the main cell wall polysaccharides of tobacco leaves using high-throughput and fractionation techniques

Nicotiana species are used to study agriculturally and industrially relevant processes, but limited screening methods are available for this species. A tobacco leaf cell wall preparation was fractionated using both chemical and enzymatic methods; the fractions obtained were subsequently analysed using rapid high-throughput wall profiling tools. The results confirmed previous data showing that mature tobacco leaf cell walls are predominantly composed of pectic homogalacturonans with lesser amounts of hemicellulosic arabinoxyloglucan and glucuronoxylan polymers. This confirmation provided proof that the profiling methods could generate good-quality results and paves the way for high-throughput screening of tobacco mutants where a range of biological processes, where the cell wall profile is important, are studied. A novel enzymatic oligosaccharide fingerprinting method was optimized to rapidly analyse the structure of XXGG-rich arabinoxyloglucans characteristic of Solanaceae species such as tobacco. Digestion profiles using two available xyloglucanase-specific endoglucanases: Trichoderma reseei EGII and Paenibacillus sp. xyloglucanase were compared showing that the latter enzyme has a higher specificity toward tobacco arabinoxyloglucans, and is better-suited for screening. This methodology would be suitable for species, such as tomato (Solanum lycopersicum) or potato (Solanum tuberosum), with similar XXGG-type motifs in their xyloglucan structure. © 2012 Elsevier Ltd. All rights reserved

Profiling the main cell wall polysaccharides of tobacco leaves using high-throughput and fractionation techniques

AgriwetenskappeInstituut Vir WynbiotegnologiePlease help us populate SUNScholar with the post print version of this article. It can be e-mailed to: [email protected]

Molecular-level modes of As binding to Fe(III) (oxyhydr)oxides precipitated by the anaerobic nitrate-reducing Fe(II)-oxidizing Acidovorax sp. strain BoFeN1

International audienceSorption of contaminants such as arsenic (As) to natural Fe(III) (oxyhydr)oxides is very common and has been demonstrated to occur during abiotic and biotic Fe(II) oxidation. The molecular mechanism of adsorption- and co-precipitation of As has been studied extensively for synthetic Fe(III) (oxyhydr)oxide minerals but is less documented for biogenic ones. In the present study, we used Fe and As K-edge X-ray Absorption Near Edge Structure (XANES), extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Mössbauer spectroscopy, XRD, and TEM in order to investigate the interactions of As(V) and As(III) with biogenic Fe(III) (oxyhydr)oxide minerals formed by the nitrate-reducing Fe(II)-oxidizing bacterium Acidovorax sp. strain BoFeN1. The present results show the As immobilization potential of strain BoFeN1 as well as the influence of As(III) and As(V) on biogenic Fe(III) (oxyhydr)oxide formation. In the absence of As, and at low As loading (As:Fe ≤ 0.008 mol/mol), goethite (Gt) formed exclusively. In contrast, at higher As/Fe ratios (As:Fe = 0.020-0.067), a ferrihydrite (Fh) phase also formed, and its relative amount systematically increased with increasing As:Fe ratio, this effect being stronger for As(V) than for As(III). Therefore, we conclude that the presence of As influences the type of biogenic Fe(III) (oxyhydr)oxide minerals formed during microbial Fe(II) oxidation. Arsenic-K-edge EXAFS analysis of biogenic As-Fe-mineral co-precipitates indicates that both As(V) and As(III) form inner-sphere surface complexes at the surface of the biogenic Fe(III) (oxyhydr)oxides. Differences observed between As-surface complexes in BoFeN1-produced Fe(III) (oxyhydr)oxide samples and in abiotic model compounds suggest that associated organic exopolymers in our biogenic samples may compete with As oxoanions for sorption on Fe(III) (oxyhydr)oxides surfaces. In addition HRTEM-EDXS analysis suggests that As(V) preferentially binds to poorly crystalline phases, such as ferrihydrite, while As(III) did not show any preferential association regarding Fh or Gt

Arsenic(III) and Arsenic(V) Speciation during Transformation of Lepidocrocite to Magnetite

Bioreduction of As­(V) and As-bearing iron oxides is considered to be one of the key processes leading to arsenic pollution in groundwaters in South and Southeast Asia. Recent laboratory studies with simple aqueous media showed that secondary Fe­(II)-bearing phases (e.g., magnetite and green rust), which commonly precipitate during bioreduction of iron oxides, captured arsenic species. The aim of the present study was to follow arsenic speciation during the abiotic Fe­(II)-induced transformation of As­(III)- and As­(V)-doped lepidocrocite to magnetite, and to evaluate the influence of arsenic on the transformation kinetics and pathway. We found green rust formation is an intermediate phase in the transformation. Both As­(III) and As­(V) slowed the transformation, with the effect being greater for As­(III) than for As­(V). Prior to the formation of magnetite, As­(III) adsorbed on both lepidocrocite and green rust, whereas As­(V) associated exclusively with green rust, When magnetite precipitated, As­(III) formed surface complexes on magnetite nanoparticles and As­(V) is thought to have been incorporated into the magnetite structure. These processes dramatically lowered the availability of As in the anoxic systems studied. These results provide insights into the behavior of arsenic during magnetite precipitation in reducing environments. We also found that As­(V) removal from solution was higher than As­(III) removal following magnetite formation, which suggests that conversion of As­(III) to As­(V) is preferred when using As-magnetite precipitation to treat As-contaminated groundwaters