Confounding factors and tertiary-phase control by a surfactive agent on smectite sorption of atrazine

Atrazine is a widely used commercial pesticide applied to soil for the control broadleaf weeds in agriculture. Frequent detection of atrazine in surface and subsurface waters and the potential for adverse effects on toxicity to aquatic and terrestrial life have generated numerous investigations into the mechanisms governing atrazine sorption by soils. This dissertation seeks to add to that body of knowledge by elucidating basic mechanisms and processes that influence sorption of atrazine on clays in the presence and absence of surfactants commonly used in commercial formulations. Sorption studies showed that air-dried (AD), resuspended K+-saturated PC (KPC) exhibited a significantly enhanced sorption affinity for atrazine over KPC that was never-dried (ND). X-ray diffraction (XRD) analysis revealed that air-drying had irreversibly collapsed the basal spacing of KPC. It was hypothesized that the atrazine sorption was enhanced in the collapsed KPC because it provided a less hydrated environment where atrazine\u27s alkylamino sidechains could simultaneously interact with hydrophobic nanosites on both of the opposing basal surfaces. Furthermore, this work explored the potential of a nonionic surfactant, Brij 35, which is similar to the surfactant used in commercial atrazine formulations, to modify the sorption chemistry of atrazine. Experiments revealed that lower concentrations of Brij 35 inhibited atrazine sorption while higher concentrations enhanced sorption; an opposite trend from what was expected. At low Brij 35 concentrations, XRD evidence indicated that Brij 35 was intercalated and progressively filled the clay interlayer. At high concentration, interlayer sites were completely filled with Brij 35 and excess surfactant formed micelles on the external surfaces of the smectite quasicrystals. Atrazine sorption was enhanced by partitioning to these surface micelles. Effects of co-solvents on surface micelle formation are discussed

Aerobic power, huddling and the efficiency of torpor in the South American marsupial, Dromiciops gliroides.

During periods of cold, small endotherms depend on a continuous supply of food and energy to maintain euthermic body temperature (T(b)), which can be challenging if food is limited. In these conditions, energy-saving strategies are critical to reduce the energetic requirements for survival. Mammals from temperate regions show a wide arrange of such strategies, including torpor and huddling. Here we provide a quantitative description of thermoregulatory capacities and energy-saving strategies in Dromiciops gliroides, a Microbiotherid marsupial inhabiting temperate rain forests. Unlike many mammals from temperate regions, preliminary studies have suggested that this species has low capacity for control and regulation of body temperature, but there is still an incomplete picture of its bioenergetics. In order to more fully understand the physiological capacities of this "living fossil", we measured its scope of aerobic power and the interaction between huddling and torpor. Specifically, we evaluated: (1) the relation between basal (BMR) and maximum metabolic rate (MMR), and (2) the role of huddling on the characteristics of torpor at different temperatures. We found that BMR and MMR were above the expected values for marsupials and the factorial aerobic scope (from [Formula: see text]CO(2)) was 6.0±0.45 (using [Formula: see text]CO(2)) and 6.2±0.23 (using [Formula: see text]O(2)), an unusually low value for mammals. Also, repeatability of physiological variables was non-significant, as in previous studies, suggesting poor time-consistency of energy metabolism. Comparisons of energy expenditure and body temperature (using attached data-loggers) between grouped and isolated individuals showed that at 20°C both average resting metabolic rate and body temperature were higher in groups, essentially because animals remained non-torpid. At 10°C, however, all individuals became torpid and no differences were observed between grouped and isolated individuals. In summary, our study suggests that the main response of Dromiciops gliroides to low ambient temperature is reduced body temperature and torpor, irrespective of huddling. Low aerobic power and low time-consistency of most thermoregulatory traits of Dromiciops gliroides support the idea of poor thermoregulatory abilities in this species

Effect of motion smoothness on the flash-lag illusion

AbstractTwo flash-lag experiments were performed in which the moving object was flashed in a succession of locations creating apparent motion and the inter-stimulus distance (ISD) between those locations was varied. In the first (n=10), the size of the flash-lag illusion was a declining non-linear function of the ISD and the largest reduction in its magnitude corresponded closely to the value where observers judged the continuity of optimal apparent motion to be lost. In the second (n=11) with large ISDs, we found the largest illusions when the flash initiated the movement, and no effect was observed when the flash terminated the movement. The data support motion position biasing or temporal integration accounts of the illusion with processing predominantly based on motion after the flash

Sex differences in metabolic rates in field crickets and their dipteran parasitoids

Sex differences in metabolic rate (MR) can result from dimorphism in the performance of energetically demanding activities. Male crickets (Teleogryllus oceanicus) engage in costly calling and aggressive activity not performed by females. Consistent with this difference, we found higher maximal MR, factorial scope, and fat content in males than females. T. oceanicus song is also costly because it attracts the parasitoid fly Ormia ochracea. Parasitized crickets had reduced maximal MR consistent with a metabolic cost to harboring larvae. This cost was greater for females, either because females invest more heavily into reproduction at the expense of metabolic capacity, or because males are under stronger selection to respond to infection. Little is known about O. ochracea outside of its auditory system and parasitic lifestyle. We observed greater resting MR in male flies, possibly reflecting a sex difference in the requirement for metabolic power output, because male flies perform potentially costly mating behavior not seen in females. We found a positive relationship between larval density within a cricket and pupal resting MR, suggesting that crickets in good condition are able to both harbor more larvae and produce larvae with higher resting MR. These results reveal a complex interplay between the metabolism of crickets and their fly parasitoids

Peptidases and the Renin-Angiotensin System: The Alternative Angiotensin-(1-7) Cascade

The renin-angiotensin system (RAS) constitutes a key hormonal system in the physiological regulation of blood pressure via peripheral and central mechanisms. Dysregulation of the RAS is considered a major factor in the development of cardiovascular pathologies, and pharmacologic blockades of this system by the inhibition of angiotensin-converting enzyme (ACE) or antagonism of the angiotensin type 1 receptor (AT1R) are effective therapeutic regimens. The RAS is now defined as a system composed of different angiotensin peptides with diverse biological actions mediated by distinct receptor subtypes. The classic RAS comprises the ACE-Ang II-AT1R axis that promotes vasoconstriction, water intake, sodium retention and increased oxidative stress, fibrosis, cellular growth, and inflammation. The nonclassical or alternative RAS is composed primarily of the ACE2-Ang-(1-7)-AT7R pathway that opposes the Ang II-AT1R axis. In lieu of the complex aspects of this system, the current review assesses the enzymatic cascade of the alternative Ang-(1-7) axis of the RAS