Analytical and experimental studies of thermionically emitting electrodes in contact with dense, seeded plasmas

Interactions are considered between a moving, alkali-metal seeded, dense plasma and a metallic electrode whose surface properties are influenced by the absorption of seed particles. The plasma behavior is governed by a set of differential equations, which are coupled to the surface through the boundary conditions. These conditions are obtained by utilizing the particle desorption rate expressions of Levine and Gyftopoulos. The solution of the problem yields the state of the surface as well as the spatial distribution of plasma properties. In particular, electrode voltage drops are predicted, which indicate whether the electrode operates in a thermionic or arc mode. The method has been applied to a potassiwn-seeded argon plasma in contact with a tungsten electrode in a stagnation flow geometry. The results show that the plasma - surface interaction may lead to large electrode currents at moderate voltage drops. These currents can be up to an order of magnitude greater than what the random electron current would be at the surface under conditions of perfect thermodynamic equilibrium at the surface temperature. R.esults of a comparable experiment show reasonably good agreement with the theory

Development of an Experimental Data Base to Validate Compressor-Face Boundary Conditions Used in Unsteady Inlet Flow Computations

The ability to predict the dynamics of integrated inlet/compressor systems is an important part of designing high-speed propulsion systems. The boundaries of the performance envelope are often defined by undesirable transient phenomena in the inlet (unstart, buzz, etc.) in response to disturbances originated either in the engine or in the atmosphere. Stability margins used to compensate for the inability to accurately predict such processes lead to weight and performance penalties, which translate into a reduction in vehicle range. The prediction of transients in an inlet/compressor system requires either the coupling of two complex, unsteady codes (one for the inlet and one for the engine) or else a reliable characterization of the inlet/compressor interface, by specifying a boundary condition. In the context of engineering development programs, only the second option is viable economically. Computations of unsteady inlet flows invariably rely on simple compressor-face boundary conditions (CFBC's). Currently, customary conditions include choked flow, constant static pressure, constant axial velocity, constant Mach number or constant mass flow per unit area. These conditions are straightforward extensions of practices that are valid for and work well with steady inlet flows. Unfortunately, it is not at all likely that any flow property would stay constant during a complex system transient. At the start of this effort, no experimental observation existed that could be used to formulate of verify any of the CFBC'S. This lack of hard information represented a risk for a development program that has been recognized to be unacceptably large. The goal of the present effort was to generate such data. Disturbances reaching the compressor face in flight may have complex spatial structures and temporal histories. Small amplitude disturbances may be decomposed into acoustic, vorticity and entropy contributions that are uncoupled if the undisturbed flow is uniform. This study is focused on the response of an inlet/compressor system to acoustic disturbances. From the viewpoint of inlet computations, acoustic disturbances are clearly the most important, since they are the only ones capable of moving upstream. Convective and entropy disturbances may also produce upstream-moving acoustic waves, but such processes are outside the scope of the present study

Functional diversity investigation of bacterial communities in distinct soil types with RISA after preculturing (RISA-APC) method

Microorganisms play a leading role in soil development and preservation; moreover, they could indicate the soil health and conditions. In this study, we analyzed the bacterial composition of three different soil types with a newly developed RISA-APC method. A novelty of this method is the pre-culturing step: this preculturing of the bacterial communities were performed on solid media supplemented with different carbon sources (e.g.: carboxy-methyl cellulose, xylan, chitin, starch, tributyrin, casein and protocatechuic acid). For the investigation of heavy metal tolerant bacteria, a preculturing on YEG media containing CuSO4 or CdCl2 were used. The mini-colonies developed after a short incubation time was investigated. This RISA-APC method proved to be a useful tool for the comparison of different soil types, and for the examination of changes in the soil bacterial community structure. It was clearly shown that the most diverse functional diversity values occurred in the forest soil and the less diverse bacterial community was detected in sandy soil samples

Extracellular enzyme systems of antagonistic Bacillus strains isolated from tomato rhizosphere

Chitinolytic, proteolytic and lipolytic enzymes could be important in the biological control of soil borne plant-pathogenic microorganisms by antagonistic microbes and in this way besides antibiotic production, the secretion of certain extracellular enzymes also could have great importance in the effectiveness of biocontrol bacilli. Some of these enzymes could directly promote the inhibition processes, while others could help the competition of the bacilli against other rhizosphere microbes. In case of five Bacillus strains, which showed excellent antagonistic effects against phytopathogenic fungi and bacteria, the secretion of some components of the protease, chitinase, cellulase, lipase and β-1,3-glucanase enzyme systems were investigated under inductive and non-inductive circumstances. Enzyme activities were measured both with classical methods and with other experimental approaches based on chromogenic enzyme substrates. The best biocontrol strains constitutively secreted chymotrypsin-like proteases and/or trypsin-like proteases, and lipases. On the contrary, the chitinase components were only secreted in chitin containing media. Cellulases and β-1,3- glucanases were produced only at very low level either in inductive media

Unsteady flow in a supercritical supersonic diffuser

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77051/1/AIAA-10045-786.pd

Comparative characterization of some fungal laccases

Laccase producing fungi were isolated from environmental samples. They were identified on the basis of ITS (Internal Transcribed Spacer) sequence analysis. The laccase production of the isolates were investigated and compared with those of other strains deriving from the Szeged Microbiological Collection and from mushroom producer’s spawn. The enzyme production were examined in various (e.g. basic, mineral and inducer containing) liquid media. The pH optimum determinations for laccase activities were carried out in cell free ferment broths, at pH 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7 and 8, applying 25 mM succinate buffer. The investigations were based on ABTS [2,2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate)] substrate measurement method. The results showed that under these conditions, among the ascomycetes strains investigated the best laccase producer was a Rhizoctonia solani isolate (the SzMC 6252J strain). Among the basidiomycetes tested, the best laccase producer was a Ganoderma isolate (HM3)

Antidermatophytic effect of Bacillus mojavensis SZMC 22228 and its secreted chymotrypsin-like protease

The aim of the present study was to investigate the antifungal effect of Bacillus mojavensis SZMC 22228 against different dermatophytes and to isolate the antidermatophytic compound from the bacterial ferment broth. B. mojavensis SZMC 22228 and its cell-free ferment broth effectively inhibited the growth of clinical reference strain of Microsporum canis, Microsporum gypseum, Trichophyton mentagrophytes, Trichophyton rubrum and Trichophyton tonsurans in agar diffusion test in vitro. An antidermatophytic, ~25 kDa protein (B. mojavensis SZMC 22228 antidermatophyitc protein, BMAP) was purified from the antifungally active, cell-free ferment broth using size exclusion and ion-exchange chromatography. BMAP showed antifungal effect against all of the investigated dermatophytes both in agar diffusion and broth microdilution susceptibility tests. M. gypseum proved to be the most susceptible dermatophyte to BMAP (MIC=40 μg/ml), all the other investigated fungi were less susceptible (MIC=80 μg/ml). The enzymatic activity of this protein was investigated in microtiter plate assay using hydrolase specific chromogenic substrates. BMAP showed high proteolytic activity towards N-Succ-Ala-Ala-Pro-Phe-pNA, and proved to be a chymotrypsin-like protease. These results suggest that the antidermatohytic activity of B. mojavensis SZMC 22228 correlates with its chymotrypsin-like protease production. After further investigations, the purified BMAP could be a promising base of a novel antidermatophytic strategy

Influence of culture conditions on the antibiotic production of antagonistic Bacillus strains isolated from tomato rhizosphere

Many phytopathogenic bacteria and fungi attack tomato plants both in seedling (e.g. Rhizoctonia solani, Pythium debaryanum) and in developed foliar state (e.g. Phytophthora infestans, Botrytis cinerea, Alternaria solani, Xanthomonas vesicatoria, Pseudomonas syringae pv. tomato, Clavibacter michiganensis). It would be desirable to find an efficient biocontrol approach for preventing the destructive effect of these pathogens. In the frame of this study, more than 250 bacteria with antagonistic properties were isolated and characterized. Results of the preliminary antagonism tests revealed that the strains belonging into the genus Bacillus were the most efficient agents against the tomato pathogenic bacteria and fungi. The Bacillus strains with the best antagonistic traits were investigated in detail. The antibiotics present in the cell-free ferment broths were detected and analysed by thin layer chromatography. Specific PCR-based approach was developed and used for the detection of the distinct antibiotic-synthesis gene clusters (iturin, surfactin, fengycin, bacillomycin and mycosubtilin) in the genomes of the strains. Our investigation revealed that the best antagonistic strains produced high amount of surfactin and/or fengycin antibiotics. On the basis of these experiments two strains were selected for further investigations. The influence of the Cu2+ and Fe2+ ions and the quality of carbon and nitrogen sources were tested in liquid culture for the antibiotic production levels by the strains. Both copper and iron highly elevated the production rate at least of the tyrosine containing antibiotics. The applied carbon and nitrogen sources highly influenced both the quantity and quality of the antibiotic mixture secreted by the strain B23 of Bacillus subtilis