Midweek Intensification of Rain in the U.S.: Does Air Pollution Invigorate Storms?

The effect of pollution on rainfall has been observed to depend both on the type of pollution and the precipitating environment. The climatological consequences of pollution for rainfall are uncertain. In some urban areas, pollution varies with the day of the week because of weekly variations in human activity, in effect providing a repeated experiment on the effects of pollution. Weekly variations in temperature, pressure, cloud characteristics, hails and lightning are observed in many areas. Observing a weekly cycle in rainfall statistics has proven to be more difficult, although there is some evidence for it. Here we examine rainfall statistics from the Tropical Rainfall Measuring Mission (TRMM) satellite over the southern U.S. and adjacent waters, and find that there is a distinct, statistically significant weekly cycle in summertime rainfall over the southeast U.S., as well as weekly variations in rainfall over the nearby Atlantic and the Gulf of Mexico. Rainfall over land peaks in the middle of the week, suggesting that summer rainfall on large scales may increase as pollution levels rise. Both rain statistics over land and what appear to be compensating effects over adjacent seas support the suggestion that air pollution invigorates convection and outflow aloft

Enhancement of FGF-like polypeptides in the retinae of newborn mice exposed to hyperoxia

AbstractRetinae from neonatal mice exposed to prolonged hyperoxia (100% oxygen), show marked vasoproliferation. Extracts of such retinae were chromatographed on a heparin-Sepharose column and the absorbed material subjected to HPLC fractionation. Two components, approx. 10 and 18 kDa, respectively, were found to have angiogenic activity, which was higher than in corresponding extracts from animals exposed to air. Both fractions and an additional 5 kDa component reacted with an antibody to basic fibroblast growth factor (bFGF) and showed higher levels in hyperoxia. The data suggest that hyperoxia activates angiogenic factors belonging to the heparin binding family

Evaporative sodium salt crust development and its wind tunnel derived transport dynamics under variable climatic conditions

Playas (or ephemeral lakes) can be significant sources of dust, but they are typically covered by salt crusts of variable mineralogy and these introduce uncertainty into dust emission predictions. Despite the importance of crust mineralogy to emission potential, little is known about (i) the effect of short-term changes in temperature and relative humidity on the erodibility of these crusts, and (ii) the influence of crust degradation and mineralogy on wind speed threshold for dust emission. Our understanding of systems where emission is not driven by impacts from saltators is particularly poor. This paper describes a wind tunnel study in which dust emission in the absence of saltating particles was measured for a suite of climatic conditions and salt crust types commonly found on Sua Pan, Botswana. The crusts were found to be non-emissive under climate conditions characteristic of dawn and early morning, as compared to hot and dry daytime conditions when the wind speed threshold for dust emission appears to be highly variable, depending upon salt crust physicochemistry. Significantly, sodium sulphate rich crusts were found to be more emissive than crusts formed from sodium chloride, while degraded versions of both crusts had a lower emission threshold than fresh, continuous crusts. The results from this study are in agreement with in-situ field measurements and confirm that dust emission from salt crusted surfaces can occur without saltation, although the vertical fluxes are orders of magnitude lower (∼10 μg/m/s) than for aeolian systems where entrainment is driven by particle impact

Epigenetic regulation of centromeric chromatin: old dogs, new tricks?

The assembly of just a single kinetochore at the centromere of each sister chromatid is essential for accurate chromosome segregation during cell division. Surprisingly, despite their vital function, centromeres show considerable plasticity with respect to their chromosomal locations and activity. The establishment and maintenance of centromeric chromatin, and therefore the location of kinetochores, is epigenetically regulated. The histone H3 variant CENP-A is the key determinant of centromere identity and kinetochore assembly. Recent studies have identified many factors that affect CENP-A localization, but their precise roles in this process are unknown. We build on these advances and on new information about the timing of CENP-A assembly during the cell cycle to propose new models for how centromeric chromatin is established and propagated

Organization and temporal expression of a flagellar basal body gene in Caulobacter crescentus.

Caulobacter crescentus assembles a single polar flagellum at a defined time in the cell cycle. The protein components of the flagellar hook and filament are synthesized just prior to their assembly. We demonstrated that the expression of a gene, flaD, that is involved in the formation of the flagellar basal body is under temporal control and is transcribed relatively early in the cell cycle, before the hook and flagellin genes are transcribed. Thus, the order of flagellar gene transcription reflects the order of assembly of the protein components. A mutation in the flaD gene results in the assembly of a partial basal body which is missing the outermost P and L rings as well as the external hook and filament (K.M. Hahnenberger and L. Shapiro, J. Mol. Biol. 194:91-103, 1987). The flaD gene was cloned and characterized by nucleotide sequencing and S1 nuclease protection assays. In contrast to the protein components of the hook and filament, the protein encoded by the flaD gene contains a hydrophobic leader peptide. The predicted amino acid sequence of the leader peptide of flaD is very similar to the leader peptide of the flagellar basal body P ring of Salmonella typhimurium (M. Homma, Y. Komeda, T. Iino, and R.M. Macnab, J. Bacteriol. 169:1493-1498, 1987)