On the theory of coronal heating mechanisms

Theoretical models describing solar coronal heating mechanisms are reviewed in some detail. The requirements of chromospheric and coronal heating are discussed in the context of the fundamental constraints encountered in modelling the outer solar atmosphere. Heating by acoustic processes in the 'nonmagnetic' parts of the atmosphere is examined with particular emphasis on the shock wave theory. Also discussed are theories of heating by electrodynamic processes in the magnetic regions of the corona, either magnetohydrodynamic waves or current heating in the regions with large electric current densities (flare type heating). Problems associated with each of the models are addressed

The influence of hypercapnia and the infaunal brittlestar <i>Amphiura filiformis</i> on sediment nutrient flux – will ocean acidification affect nutrient exchange?

Rising levels of atmospheric carbon dioxide and the concomitant increased uptake of this by the oceans is resulting in hypercapnia-related reduction of ocean pH. Research focussed on the direct effects of these physicochemical changes on marine invertebrates has begun to improve our understanding of impacts at the level of individual physiologies. However, CO₂-related impairment of organisms' contribution to ecological or ecosystem processes has barely been addressed. The burrowing ophiuroid <i>Amphiura filiformis</i>, which has a physiology that makes it susceptible to reduced pH, plays a key role in sediment nutrient cycling by mixing and irrigating the sediment, a process known as bioturbation. Here we investigate the role of <i>A. filiformis</i> in modifying nutrient flux rates across the sediment-water boundary and the impact of CO₂- related acidification on this process. A 40 day exposure study was conducted under predicted pH scenarios from the years 2100 (pH 7.7) and 2300 (pH 7.3), plus an additional treatment of pH 6.8. This study demonstrated strong relationships between <i>A. filiformis</i> density and cycling of some nutrients; <iA. filiformis</i> activity increases the sediment uptake of phosphate and the release of nitrite and nitrate. No relationship between <i>A. filiformis</i> density and the flux of ammonium or silicate were observed. Results also indicated that, within the timescale of this experiment, effects at the individual bioturbator level appear not to translate into reduced ecosystem influence. However, long term survival of key bioturbating species is far from assured and changes in both bioturbation and microbial processes could alter key biogeochemical processes in future, more acidic oceans

Concentrations of Insulin-Like Growth Factor-I in Blood and Ovarian Follicular Fluid of Cattle Selected for Twins

Recent studies have implicated insulin-like growth factor I (IGF-I) as an intraovarian regulator of follicular growth and differentiation. Therefore, we investigated the possibility that cattle selected for twin births may have increased concentrations of IGF-I within the ovarian follicle and(or) in peripheral blood. The estrous cycles of 14 cows with histories of producing twins and 12 control monotocous cows were synchronized with 35 mg of prostaglandin F2α (PGF2α). Blood and follicular fluid were collected 48-50 h post-administration of PGF2α. (follicular phase of the estrous cycle). Concentrations of IGF-I were measured by RJA after acid-ethanol treatment of serum or follicular fluid. Twin-producing cows had a greater (p \u3c 0.05) number of large (\u3e4 mm) follicles and 47% greater (p \u3c 0.05) concentrations of IGF-I in peripheral blood than control cows. Cattle selected for high twinning frequency also had greater (p \u3c 0.05) concentrations of IGF-I (±SE) in the two largest follicles than control (unselected) cows (327 ± 28 vs. 243 ± 29 ng/ml). IGF-I concentrations in pooled small (1-3.9 mm) follicles were less (p \u3c 0.05) than in large follicles but did not differ between control and twin-producing cattle. In addition, the percentage of IGF-I concentrations measured in follicular fluid to that of serum was lower (P \u3c 0.05) in small follicles than in large follicles, and was greater (p \u3c0.05) in large follicles of control (93.2 ± 5.3%) than twin-producing (76.2 ± 4.4%) cattle. Moreover, concentrations of IGF-I in serum and follicular fluid were correlated positively (r = 0.69, p \u3c 0.01). Concentrations of estradiol and progesterone in follicular fluid of small or large follicles did not differ between control and twin-producing cattle. Collectively, the present study provides evidence suggesting that natural twinning in cattle is associated with increased concentrations of IGF-I in both blood and follicular fluid. These data are consistent with the hypothesis that IGF-I plays a role in the regulation of folliculogenesis and is a mediator of a genetic component of multiple ovulations in cattle