Quantification of uncertainty in aerodynamic heating of a reentry vehicle due to uncertain wall and freestream conditions

The primary focus of this study is to demonstrate an efficient approach for uncertainty quantification of surface heat flux to the spherical non-ablating heatshield of a generic reentry vehicle due to epistemic and aleatory uncertainties that may exist in various parameters used in the numerical solution of hypersonic, viscous, laminar blunt-body flows with thermo-chemical non-equilibrium. Two main uncertainty sources were treated in the computational fluid dynamics (CFD) simulations: (1) aleatory uncertainty in the freestream velocity and (2) epistemic uncertainty in the recombination efficiency for a partially catalytic wall boundary condition. The Second-Order Probability utilizing a stochastic response surface obtained with Point-Collocation Non-Intrusive Polynomial Chaos was used for the propagation of mixed (aleatory and epistemic) uncertainties. The uncertainty quantication approach was validated on a stochastic model problem with mixed uncertainties for the prediction of stagnation point heat transfer with Fay-Riddell relation, which included the comparison with direct Monte Carlo sampling results. In the stochastic CFD problem, the uncertainty in surface heat transfer was obtained in terms of intervals at different probability levels at various locations including the stagnation point and the shoulder region. The mixed uncertainty results were compared to the results obtained with a purely aleatory uncertainty analysis to show the difference between two uncertainty quantication approaches. A global sensitivity analysis indicated that the velocity has a stronger contribution to the overall uncertainty in the stagnation point heat transfer for the range of input uncertainties considered in this study --Abstract, page iii

Quaternary loess-paleosol sequences as examples of climate-driven sedimentary extremes

Loess is a widespread, wind-transported, silt-dominated deposit that contains geologic archives of atmospheric circulation and paleoclimate on continents. Loess may cover as much as 10% of the Earth’s land surface. It is composed mainly of quartz, feldspars, and clay minerals, with varying amounts of carbonate minerals. The geochemistry of loess differs from region to region, depending on source materials, but all loess is very high in SiO2 with lesser amounts of other major elements. Trends in loess downwind from source areas include systematic decreases in thickness and amounts of sand and coarse silt, and increases in amounts of fine silt and clay. Loess particle size also varies at a given locality over time within individual depositional packages. This variability may be a function of changing wind strengths, different source sediments, or some combination of the two. The classical concept of loess is that it is a product of glacial grinding, with subsequent entrainment by wind from outwash deposits. However, it is now known that other processes contribute to silt particle formation, including frost shattering, salt weathering, fluvial and colluvial comminution, eolian abrasion, and ballistic impact. Much debate has taken place over the concept of “desert” (nonglaciogenic) loess, which is widespread in some regions but of limited distribution elsewhere. Nevertheless, glacial silt production probably exceeds the amount of silt generated by all other processes. Much of the loess in or adjacent to deserts may be inherited silt-sized particles from siltstone, mudstone, shale, and volcanic ash. In many regions, loess is near dune fields or eolian sand sheets. A question that arises from this geographic assocation is whether or not eolian sand and loess should be considered facies of the same depositional unit. There are regions such as China where these deposits are interbedded, which supports the facies concept. In other regions, such as North America, detailed geochemical and isotopic analyses show that the majority of loess particles were derived from a different, and more distant source than eolian sand. Key to understanding loess stratigraphy and interpreting environments of the past is the recognition of buried soils (paleosols). Ancient soils can be recognized by their distinctive morphological features and by vertical changes in particle size, chemistry, and mineralogy. Paleosols represent past periods when loess sedimentation rates decreased to zero or slowed significantly. Thus, loess and their interstratified soils represent end members of a continuum of sedimentary extremes: high rates of sedimentation yield relatively unaltered loess in the stratigraphic record, whereas low or episodic rates of sedimentation commonly leave a record of buried soils. The shift between these sedimentary extremes is preserved in the long-term glacial-interglacial record of the Quaternary. Although it is now known that not all eolian silt is glaciogenic, in almost all loess regions, eolian sedimentation rates were much higher during glacial periods than during interglacial periods. Drier, colder climates, a decreased intensity of the hydrologic cycle, stronger or more-persistent winds, increased sediment supply, decreased vegetation cover, and increased sediment availability all probably contributed to the sedimentary “extreme” of rapid loess accumulation during the last glacial period. The present interglacial period represents an opposite sedimentary “extreme” of minimal loess sedimentation and i

Localization of Angiotensin Converting Enzyme in Rabbit Cornea and Its Role in Controlling Corneal Angiogenesis \u3cem\u3ein vivo\u3c/em\u3e

Purpose: The renin angiotensin system (RAS) has been shown to modulate vascular endothelial growth factor and angiogenesis. In this study we investigated (i) the existence of the RAS components angiotensin converting enzyme (ACE) and angiotensin II receptors (AT1 and AT2) in the rabbit cornea using in vitro and ex vivo models and (ii) the effect of enalapril, an ACE inhibitor, to inhibit angiogenesis in rabbit cornea in vivo. Methods: New Zealand White rabbits were used. Cultured corneal fibroblasts and corneal epithelial cells were used for RNA isolation and cDNA preparation using standard molecular biology techniques. PCR was performed to detect the presence of ACE, AT1, and AT2 gene expression. A corneal micropocket assay to implant a vascular endothelial growth factor (VEGF) pellet in the rabbit cornea was used to induce corneal angiogenesis. Rabbits of the control group received sterile water, and the treated group received 3 mg/kg enalapril intramuscularly once daily for 14 days starting from day 1 of pellet implantation. The clinical eye examination was performed by slit-lamp biomicroscopy. We monitored the level of corneal angiogenesis in live animals by stereomicroscopy at days 4, 9, and 14 after VEGF pellet implantation. Collagen type IV and lectin immunohistochemistry and fluorescent microscopy were used to measure corneal angiogenesis in tissue sections of control and enalapril-treated corneas of the rabbits. Image J software was used to quantify corneal angiogenesis in the rabbit eye in situ. Results: Our data demonstrated the presence of ACE, AT1, and AT2 expression in corneal fibroblasts. Cells of corneal epithelium expressed AT1 and AT2 but did not show ACE expression. Slit-lamp examination did not show any significant difference between the degree of edema or cellular infiltration between the corneas of control and enalapril-treated rabbits. VEGF pellet implantation caused corneal angiogenesis in the eyes of vehicle-treated control rabbits, and the mean area of corneal neovascularization was 1.8, 2.8, and 3.2 mm2 on days 4, 9, and 14, respectively. Enalapril treatment caused a notable decrease in corneal neovascularization of 44% (1 mm2), 28% (2.1 mm2), and 31% (2.2 mm2) on the three tested time points, respectively. The immunostaining of corneal tissue sections with collagen type IV and lectin confirmed the presence of blood vessels, with enalapril-treated rabbit corneas showing a lesser degree of blood vessel staining. Conclusions: Corneal cells show expression of tissue RAS components, such as ACE, AT1, and AT2. Treatment with ACE inhibitor enalapril markedly decreased corneal angiogenesis in a rabbit model of VEGF-induced corneal neovascularization, suggesting that ACE inhibitors may represent a novel therapeutic strategy to treat corneal angiogenesis

Origin of last-glacial loess in the western Yukon-Tanana Upland, central Alaska, USA

Loess is widespread over Alaska, and its accumulation has traditionally been associated with glacial periods. Surprisingly, loess deposits securely dated to the last glacial period are rare in Alaska, and paleowind reconstructions for this time period are limited to inferences from dune orientations. We report a rare occurrence of loess deposits dating to the last glacial period, ~19 ka to ~12 ka, in the Yukon-Tanana Upland. Loess in this area is very coarse grained (abundant coarse silt), with decreases in particle size moving south of the Yukon River, implying that the drainage basin of this river was the main source. Geochemical data show, however, that the Tanana River valley to the south is also a likely distal source. The occurrence of last-glacial loess with sources to both the south and north is explained by both regional, synoptic-scale winds from the northeast and opposing katabatic winds that could have developed from expanded glaciers in both the Brooks Range to the north and the Alaska Range to the south. Based on a comparison with recent climate modeling for the last glacial period, seasonality of dust transport may also have played a role in bringing about contributions from both northern and southern sources

Geochemical and mineralogical evidence for Sahara and Sahel dust additions to Quaternary soils on Lanzarote, eastern Canary Islands, Spain

Africa is the most important source of dust in the world today, and dust storms are frequent on the nearby Canary Islands. Previous workers have inferred that the Sahara is the most important source of dust to Canary Islands soils, with little contribution from the Sahel region. Soils overlying a late Quaternary basalt flow on Lanzarote, Canary Islands, contain, in addition to volcanic minerals, quartz and mica, exotic to the island!s bedrock. Kaolinite in the soils also likely has an exotic origin. Trace-element geochemistry shows that the soils are derived from varying proportions of locally derived basalt and African dust. Major-element geochemistry, clay mineralogy and interpretation of satellite imagery suggest that dust additions to the Canary Islands come not only from the Sahara Desert, but also from the Sahel region

Surficial geologic materials of the Marion Quadrangle, Iowa

https://ir.uiowa.edu/igs_ofm/1002/thumbnail.jp