No abstract

The dispersion and stability of nanofluids obtained by dispersing Al2O3 nanoparticles (obtained from different sources) in water have been analyzed. The differences arising from different dispersion techniques, the resulting particle size distribution, and time stability among the different samples are evaluated. Then the volumetric behavior up to high pressures (25 MPa) and atmospheric pressure viscosity were experimentally determined. It has been found that the influence of particle size in density is subtle but not negligible, but the differences in viscosity are very large and must be taken into account for any practical application. These viscosity differences can be rationalized by considering a theory describing the aggregation state of the nanofluid.

Fungi possess efficient mechanisms of pH and ion homeostasis, allowing them to grow over a wide range of environmental conditions. In this study, we addressed the role of the pH response transcription factor PacC in salt tolerance of the vascular wilt pathogen Fusarium oxysporum. Loss-of-function pacC ؉/؊ mutants showed increased sensitivity to Li ؉ and Na ؉ and accumulated higher levels of these cations than the wild type. In contrast, strains expressing a dominant activating pacC c allele were more salt tolerant and had lower intracellular Li ؉ and Na ؉ concentrations. Although the kinetics of Li ؉ influx were not altered by mutations in pacC, we found that Li ؉ efflux at an alkaline, but not at an acidic, ambient pH was significantly reduced in pacCloss-of-function mutants. To explore the presence of a PacC-dependent efflux mechanism in F. oxysporum, we cloned ena1 encoding an orthologue of the yeast P-type Na ؉ -ATPase ENA1. Northern analysis revealed that efficient transcriptional activation of ena1 in F. oxysporum required the presence of high Na ؉ concentrations and alkaline ambient pH and was dependent on PacC function. We propose a model in which PacC controls ion homeostasis in F. oxysporum at a high pH by activating expression of ena1 coordinately with a second Na ؉ -responsive signaling pathway.Fungi are a versatile class of organisms that have successfully occupied numerous ecological niches, including those of plant and animal pathogenesis. A striking property of fungi and a major determinant of their evolutionary success is their capacity to adapt to an extremely wide range of environmental conditions. This ability depends crucially on the presence of cellular sensory networks that monitor the environment and mediate changes in gene expression in response to shifts in the external conditions. We use the vascular wilt pathogen Fusarium oxysporum as a model to understand how environmental signals regulate gene expression in fungi and how these regulatory mechanisms determine fungal virulence.A key factor in fungal growth and development is ambient pH. Fungi grow over a wide range of pH conditions and must thus be able to tailor gene expression to the particular pH of their growth environment. A conserved signaling cascade integrated by the products of the pal genes, whose terminal component is the zinc-finger transcription factor PacC/ Rim101p, regulates gene expression in response to ambient pH (18). Upon shift to alkaline pH, an inactive PacC precursor is posttranscriptionally activated by proteolytic processing into a shorter functional form that activates genes preferentially expressed at alkaline pH and represses genes expressed under acidic growth conditions (18). The pacC orthologue of F. oxysporum was recently cloned, and the encoded protein was shown to regulate pH-dependent gene expression and to function as a negative regulator of virulence on plants (11). Thus, pacC ϩ/Ϫ loss-of-function mutants of F. oxysporum mimic growth at acidic ambient pH and exhibit increased virulence, whereas pac...

No abstract

No abstract