Cloning, mapping and identification of the Aeromonas salmonicida fstA, fepA and irpA genes, encoding the 86, 82 and 74 kDa iron-regulated outer membrane proteins, respectively

Three iromps (iron-regulated outer membrane proteins) of Aeromonas salmonicida were identified by the use of specific antibodies together with Southern hybridization analysis and limited nucleotide sequencing of their genes. The results of these experiments together with a search of the international database for homologous sequences led to their identification as follows: -86 kDa iromp (FstA) as a Vibrio anguillarum Fat A homologue -82 kDa iromp (FepA) as an Escherichia coli FepA homologue -74 kDa iromp (IrpA) as an Escherichia coli Cir homologue.

Studies on the outer membrane of Pseudomonas aeruginosa and associated resistance properties

The aim of this thesis was to investigate antibacterial agents for use in disinfectant formulation in conjunction with benzalkonium chloride (BKC), and if possible, to synthesise novel agents based upon successful structures. Development of resistance to antibacterial agents following long-term exposure of P. aeruginosa to BKC was also investigated, examining cross-resistance to clinically relevant antibiotics and determining mechanisms of resistance. In this study over 50 compounds were examined for antibacterial action against P. aeruginosa, both alone and in conjunction with BKC. Successful compounds were used to design novel agents, based upon the acridine ring structure, some of which showed synergy with BKC. In 15 of the 16 strains exposed to increasing concentrations of BKC, resistance to the disinfectant arose. Strains PAO1 and OO14 were examined further, each showing stable BKC resistance and a slightly varying profile of cross-resistance. In strain PAO1 alterations in the fatty acids of the cytoplasmic membrane, increase in expression of OprG, decrease in susceptibility to EDTA as an outer membrane permeabilising agent and an increase in negativity of the cell surface charge were observed as cells became more resistant to BKC. In strain OO14 a decrease in whole cell phosphatidylcholine content, a decrease in binding/uptake of BKC and an increase in cell surface hydrophobicity were observed as cells became more resistant to BKC. Resistance to tobramycin in strain OO14 was initially high, but fell as cells were adapted to BKC, this coincided with a quantitative reduction of plasmid DNA in the cells.

The effect of haem limitation and iron restriction on outer membrane proteins and on respiratory systems of non typable Haemophilus influenzae

The effects of haem limitation and iron restriction on cells of non typable Haemophilus influenzae were investigated. Haem limitation was achieved by adding concentrations of haem to growth media which resulted in substantial decreases in final cell yields. Iron restriction was achieved by substituting protoporphyrin IX (PPIX) for haem in the growth medium and adding an iron chelator to the system. The effect of these nutrient limitations on a) outer membrane composition, and b) respiratory systems of non typable H.influenzae was investigated. Several of the strains examined produced new PPIX-specific outer membrane proteins when cultured utilising PPIX as a porphyrin source. The immune response of patients with bronchiectasis to outer membrane antigens of H.influenzae cultured under iron-restricted conditions was analysed by ELISA and immunoblotting techniques. ELISA analysis revealed that individuals with severe bronchiectasis had high titres of antibodies directed against H.influenzae OMs in both serum and sputum. Immunoblotting with homologous serum showed that where PPIX-specific OMPs were produced they were antigenic and were recognised by patients' serum. This suggested that these H.influenzae OMPs may be expressed in vivo. Additionally, the development of the immune responses to non typable H.influenzae outer membrane antigens was investigated using a rat lung model. Bacteria encased in agar beads were inoculated intratracheally into rat lungs, infection was established, and the immune response monitored for 6 weeks. The animals developed antibodies to PPIX-specific OMPs during the course of infection, providing further evidence that H.influenzae express these novel OMP antigens when growing in vivo. Studies in vitro on respiratory systems of phenotypically altered H.influenzae showed that bacteria grown utilising PPIX as a porphyrin source, or under conditions of iron-restriction produced ten fold fewer cytochromes than cells grown in nutrient excess, while haem limited H.influenzae produced no detectable cytochromes. Respiration of various substrates was depressed in haem limited and in PPIX-grown cultures as compared with cells grown in nutrient excess.

Laser beam self-focusing in the atmosphere

We propose to exploit a self-focusing effect in the atmosphere to assist delivering powerful laser beams from orbit to the ground. We demonstrate through numerical modeling that when the self-focusing length is comparable with the atmosphere height the spot size on the ground can be reduced well below the diffraction limits without beam quality degradation. The density variation suppresses beam filamentation and provides the self-focusing of the beam as a whole. The use of light self-focusing in the atmosphere can greatly relax the requirements for the orbital optics and ground receivers.

The influence of a coal gasifier atmosphere on fatigue crack growth rates in BS 4360 steel

Fatigue crack growth tests have been carried out in a number of gaseous environments in order to assess their effects on the crack propagation resistance of BS 4360 grade 50EE, a weldable structural steel. Crack growth rates at 25 °C are up to 20 times higher in hydrogen than in air, but there is no effect when hydrogen is present as a 30% constituent of a simplified product gas (SPG). Indeed, crack growth rates in such a mixture are slightly lower than those measured in air, being comparable with those observed in an inert environment. The other gases present in the SPG are CO, CO2 and CH4, and it is probable that the carbon monoxide is responsible for nullifying the embrittling effects of hydrogen, by preferentially adsorbing on to the surface of the steel and thus blocking hydrogen entry. Experimental observations suggest that oxygen has the same effect when small quantities are allowed to diffuse into a non-flowing hydrogen environment around a propagating crack. The results are encouraging in terms of the suitability of conventional structural steels such as BS 4360 for gas plant applications. The gas mixtures present in such an environment would not have the severe detrimental effects on fatigue crack growth resistance which result from the presence of 'pure' hydrogen. © 1993.

Influence of reaction atmosphere (H2O, N2, H2, CO2, CO) on fluidized-bed fast pyrolysis of biomass using detailed tar vapor chemistry in computational fluid dynamics

Secondary pyrolysis in fluidized bed fast pyrolysis of biomass is the focus of this work. A novel computational fluid dynamics (CFD) model coupled with a comprehensive chemistry scheme (134 species and 4169 reactions, in CHEMKIN format) has been developed to investigate this complex phenomenon. Previous results from a transient three-dimensional model of primary pyrolysis were used for the source terms of primary products in this model. A parametric study of reaction atmospheres (H2O, N2, H2, CO2, CO) has been performed. For the N2 and H2O atmosphere, results of the model compared favorably to experimentally obtained yields after the temperature was adjusted to a value higher than that used in experiments. One notable deviation versus experiments is pyrolytic water yield and yield of higher hydrocarbons. The model suggests a not overly strong impact of the reaction atmosphere. However, both chemical and physical effects were observed. Most notably, effects could be seen on the yield of various compounds, temperature profile throughout the reactor system, residence time, radical concentration, and turbulent intensity. At the investigated temperature (873 K), turbulent intensity appeared to have the strongest influence on liquid yield. With the aid of acceleration techniques, most importantly dimension reduction, chemistry agglomeration, and in-situ tabulation, a converged solution could be obtained within a reasonable time (∼30 h). As such, a new potentially useful method has been suggested for numerical analysis of fast pyrolysis.

Light self-focusing in the atmosphere:thin window model

Ultra-high power (exceeding the self-focusing threshold by more than three orders of magnitude) light beams from ground-based laser systems may find applications in space-debris cleaning. The propagation of such powerful laser beams through the atmosphere reveals many novel interesting features compared to traditional light self-focusing. It is demonstrated here that for the relevant laser parameters, when the thickness of the atmosphere is much shorter than the focusing length (that is, of the orbit scale), the beam transit through the atmosphere in lowest order produces phase distortion only. This means that by using adaptive optics it may be possible to eliminate the impact of self-focusing in the atmosphere on the laser beam. The area of applicability of the proposed "thin window" model is broader than the specific physical problem considered here. For instance, it might find applications in femtosecond laser material processing.

Outer rotor mechanical and dynamic performance analysis for high-speed machine

Due to high-speed rotation, the problems about rotor mechanics and dynamics for outer rotor high-speed machine are more serious than conventional ones, in view of above problems the mechanical and dynamics analysis for an outer rotor high-speed permanent magnet claw pole motor are carried out. The rotor stress analytical calculation model was derived, then the stress distribution is calculated by finite element method also, which is coincided with that calculated by analytical model. In addition, the stress distribution of outer rotor yoke and PMs considering centrifugal force and temperature effect has been calculated, some influence factors on rotor stress distribution have been analyzed such as pole-arc coefficient and speed. The rotor natural frequency and critical speed were calculated by vibration mode analysis, and its dynamics characteristics influenced by gyroscope effect were analyzed based on Campbell diagram. Based on the analysis results above an outer rotor permanent magnet high-speed claw pole motor is design and verified.