Sensitivity study of a valve recession model

The aim of this work was to carry out a sensitivity analysis of a valve recession model. For the sensitivity study, the effects of the param eters on the valve recession mode l were investigated, for both, light duty and heavy duty engines. It was seen that for light duty engines, the impact component parameters had the gr eatest effect on valve recession and for heavy duty engines the sliding wear component p arameters have an increasing con- tribution to the overall valve recession

Biodepuration of polynuclear aromatic hydrocarbons from a bivalve mollusk, Mercenaria mercenaria L

Mercenaria mercenaria, exposed in vitro for 48 h to nine parent polynuclear aromatic hydrocarbons (PAHs) found in waste crankcase oil (WCCO) and analysed by multiparametric analysis over a 45- day depuration period in an activated carbon filtration aquaria system, did not depurate PAHs, but rather maintained them at detectable levels. Uptake of PAHs was shown to be directly related to clam weight. A cluster analysis of empirical results reaffirmed a biostabilization in PAH groupings in clam tissue over a 45-day depuration period and exhibited no evidence of a decreasing trend in total PAHs when subjected to ANOVA. Due to the commerical importance of hard-shell clams, the practices of clam depuration and clam relyaing are reviewed in light of potential long-term public health exposures to low-level xenobiotics and implications for human consumers

Analysis of the Effects of Dam Release Properties and Ambient Groundwater Flow on Surface Water‐Groundwater Exchange Over a 100‐km‐Long Reach

Hydroelectric dams often create highly dynamic downstream flows that promote surface water‐groundwater (SW‐GW) interactions including bank storage, the temporary storage of river water in the riverbank. Previous research on SW‐GW exchanges in dammed rivers has primarily been at single study sites, which has limited the understanding of how these exchanges evolve as dam releases travel downstream. This study evaluates how dam releases affect SW‐GW exchange continuously over a 100‐km distance. This is accomplished by longitudinally routing water releases through a synthetic river and modeling bed and bank fluid and solute exchange across transverse transects spaced along the reach. Peak and square dam release hydrograph shapes with three magnitudes (0.5, 1.0, and 1.5 m) were considered. The effect of four ambient groundwater flow conditions (very slightly losing, neutral, and two gaining from the perspective of the river) was evaluated for each dam release scenario. Both types of dam release shapes cause SW‐GW interaction over the entire 100‐km distance, and our results show that square type releases cause bank storage exchange well beyond this distance. Strongly gaining conditions reduce the amount of exchange and allow flushing of river‐sourced solute out of the bank after the dam pulse has passed. Both neutral and losing conditions have larger fluid and solute flux into the bank and limit the amount of solute that returns to the river. Our results support that river corridors downstream of dams have increased river‐aquifer connectivity and that this enhanced connectivity can extend at least 100 km downstream

Enforced expression of Tbx1 in fetal thymic epithelial cells antagonizes thymus organogenesis

Enforced expression of Tbx1 in fetal thymic epithelial cells antagonizes thymus organogenesis Kim T. Cardenas The thymus and parathyroid glands originate from organ-specific domains of 3rd pharyngeal pouch (PP) endoderm. At embryonic day 11.5 (E11.5), the ventral thymus and dorsal parathyroid domains can be identified by Foxn1 and Gcm2 expression respectively. Neural crest cells, (NCCs) play a role in regulating patterning of 3rd PP endoderm. In addition, pharyngeal endoderm influences fate determination via secretion of Sonic hedgehog (Shh), a morphogen required for Gcm2 expression and generation of the parathyroid domain. Gcm2 is a downstream target of the transcription factor Tbx1, which in turn is positively regulated by Shh. Although initially expressed throughout pharyngeal pouch endoderm, Tbx1 expression is excluded from the thymus-specific domain of the 3rd PP by E10.5, but persists in the parathyroid domain. Based on these observations, we hypothesized that Tbx1 expression is non-permissive for thymus fate specification and that enforced expression of Tbx1 in the fetal thymus would impair thymus development. To test this hypothesis, we generated knock-in mice containing a Cre-inducible allele that allows for tissue-specific Tbx1 expression. Expression of the R26iTbx1 allele in fetal and adult thymus using Foxn1Cre resulted in severe thymus hypoplasia throughout ontogeny that persisted in the adult. Thymic epithelial cell (TEC) development was impaired as determined by immunohistochemical and FACS analysis of various differentiation markers. The relative level of Foxn1 expression in fetal TECs was significantly reduced. TECs in R26iTbx1/+ thymi assumed an almost universal expression of Plet-1, a marker associated with a TEC stem/progenitor cell fate. In addition, embryonic R26iTbx1/+ mice develop a perithymic mesechymal capsule that appears expanded compared to control littermates. Interestingly, thymi from neonatal and adult R26iTbx1/+ but not R26+/+ mice were encased in adipose tissue. This thymic phenotype also correlated with a decrease in thymocyte cellularity and aberrant thymocyte differentiation. The results to date support the conclusion that enforced expression of Tbx1 in TECs antagonizes their differentiation and prevents normal organogenesis via both direct and indirect effects

Coupled-cluster theory of a gas of strongly-interacting fermions in the dilute limit

We study the ground-state properties of a dilute gas of strongly-interacting fermions in the framework of the coupled-cluster expansion (CCE). We demonstrate that properties such as universality, opening of a gap in the excitation spectrum and applicability of s-wave approximations appear naturally in the CCE approach. In the zero-density limit, we show that the ground-state energy density depends on only one parameter which in turn may depend at most on the spatial dimensionality of the system.Comment: 7 figure