Mesh generation by domain bisection

The research reported in this dissertation was undertaken to investigate efficient computational methods of automatically generating three dimensional unstructured tetrahedral meshes. The work on two dimensional triangular unstructured grid generation by Lewis and Robinson [LeR76] is first examined, in which a recursive bisection technique of computational order nlog(n) was implemented. This technique is then extended to incorporate new methods of geometry input and the automatic handling of multiconnected regions. The method of two dimensional recursive mesh bisection is then further modified to incorporate an improved strategy for the selection of bisections. This enables an automatic nodal placement technique to be implemented in conjunction with the grid generator. The dissertation then investigates methods of generating triangular grids over parametric surfaces. This includes a new definition of surface Delaunay triangulation with the extension of grid improvement techniques to surfaces. Based on the assumption that all surface grids of objects form polyhedral domains, a three dimensional mesh generation technique is derived. This technique is a hybrid of recursive domain bisection coupled with a min-max heuristic triangulation algorithm. This is done to achieve a computationlly efficient and reliable algorithm coupled with a fast nodal placement technique. The algorithm generates three dimensional unstructured tetrahedral grids over polyhedral domains with multi-connected regions in an average computational order of less than nlog(n)

AIDS and food security: essays

AIDS (Disease), Food security., HIV/AIDS Africa., Africa, Sub-Saharan., Epidemics., Food security Developing countries., Food supply., Malnutrition Prevention., Agriculture., Nutrition policies. ,

In situ measurements of ship tracks

It has long been known that cloud droplet concentrations are strongly influenced by cloud condensation nuclei (CCN) and that anthropogenic sources of pollution can affect CCN concentrations. More recently it has been suggested that CCN may play an important role in climate through their effect on cloud albedo. A interesting example of the effect of anthropogenic CCN on cloud albedo is the so-called 'ship track' phenomenon. Ship tracks were first observed in satellite imagery when the ship's emissions were evidently needed for the formation of a visible cloud. However, they appear more frequently in satellite imagery as modifications to existing stratus and stratocumulus clouds. The tracks are seen most clearly in satellite imagery by comparing the radiance at 3.7 microns with that at 0.63 and 11 microns. To account for the observed change in radiance, droplet concentrations must be high, and the mean size of the droplets small, in ship tracks. Researchers describe what they believe to be the first in situ measurements in what appears to have been a ship track

Discriminating fluid source regions in orogenic gold deposits using B-isotopes

The genesis of orogenic gold deposits is commonly linked to hydrothermal ore fluids derived from metamorphic devolatilization reactions. However, there is considerable debate as to the ultimate source of these fluids and the metals they transport. Tourmaline is a common gangue mineral in orogenic gold deposits. It is stable over a very wide P–T range, demonstrates limited volume diffusion of major and trace elements and is the main host of B in most rock types. We have used texturally resolved B-isotope analysis by secondary ion mass spectrometry (SIMS) to identify multiple fluid sources within a single orogenic gold ore district. The Loulo Mining District in Mali, West Africa hosts several large orogenic gold ore bodies with complex fluid chemistry, associated with widespread pre-ore Na- and multi-stage B-metasomatism. The Gara deposit, as well as several smaller satellites, formed through partial mixing between a dilute aqueous-carbonic fluid and a hypersaline brine. Hydrothermal tourmaline occurs as a pre-ore phase in the matrix of tourmalinite units, which host mineralization in several ore bodies. Clasts of these tourmalinites occur in mineralized breccias. Disseminated hydrothermal and vein hosted tourmaline occur in textural sites which suggest growth during and after ore formation. Tourmalines show a large range in δ11B values from −3.5 to 19.8‰, which record a change in fluid source between paragenetic stages of tourmaline growth. Pre-mineralization tourmaline crystals show heavy δ11B values (8–19.8‰) and high X-site occupancy (Na ± Ca; 0.69–1 apfu) suggesting a marine evaporite source for hydrothermal fluids. Syn-mineralization and replacement phases show lighter δ11B values (−3.5 to 15.1‰) and lower X-site occupancy (0.62–0.88 apfu), suggesting a subsequent influx of more dilute fluids derived from devolatilization of marine carbonates and clastic metasediments. The large, overlapping range in isotopic compositions and a skew toward the opposing population in the δ11B data for both tourmaline groups reflects continual tourmaline growth throughout mineralization, which records the process of fluid mixing. A peak in δ11B values at ∼8‰ largely controlled by tourmalines of syn- to post-ore timing represents a mixture of the two isotopically distinct fluids. This paper demonstrates that B-isotopes in tourmaline can be instrumental in interpreting complex and dynamic hydrothermal systems. The importance of B as an integral constituent of orogenic ore forming fluids and as a gangue phase in orogenic gold deposits makes B-isotope analysis a powerful tool for testing the level of source region variability in these fluids, and by extension, that of metal sources

Preserving Venice’s Bells and Their Towers

In Venice, where Catholic Church attendance has declined, bells and bell towers have lost their purpose. Their neglect has left them vulnerable to decay and structural stresses. This project involved complex onsite surveys of 20 bell towers and 69 bells. Condition, accessibility, and safety were documented for each tower. Two thirds of the towers are in poor to only fair condition, but some percentage can be made safe with proper repairs. Photos, dimensions and other bell tower data were documented in an online application. Recommendations and concept designs for merchandise were also researched in order to establish an outline for preservation

Eighteenth Year of the Gulf of Maine Environmental Monitoring Program

This report summarizes the metals and organic contaminant data associated with the collection and analyses of blue mussel (Mytilus edulis) tissue from selected sites along the Gulf of Maine coast during the 2008 sampling season. Contaminant monitoring is conducted by the Gulfwatch Program for the Gulf of Maine Council on the Marine Environment (GOMC). A subset of these data is compared with analytical results from earlier Gulfwatch monitoring (2001-2007). Statistical analyses are limited to descriptive measures of replicates from selected sampling sites and include: arithmetic means, and appropriate measures of variance. The primary purpose of this report is to present the current annual results, present graphical representation of spatial and temporal trends and identify potential outliers in order to provide investigators and other interested persons with contemporary information concerning water quality in the Gulf of Maine, as reflected by uptake into resident shellfish (mussels and clams)

Distillers Dried Grains Supplementation of Fall-calving Cows or Calves Grazing Stockpiled Forage During Winter (Progress Report)

Six 10-acre pastures containing Fawn endophyte-free tall fescue were strip-grazed by 4 pregnant fall-calving cows with calves from mid-November through March. Treatments applied to the cows in the six pastures included: Minimal supplementation (Minimal treatment), creep feeding a DDGS-soy hull pellet to calves (Creep treatment), or DDGS supplementation to cows (DDGS treatment). Cow weights and body condition scores and calf weights were measured over the winter grazing season. Over the season, calves in the Creep treatment had greater body weight gains than calves in the DDGS and Minimal treatments (3.1, 2.3, and 2.2 lbs/day, respectively). Partly because of a dry period while stockpiling forage and cold temperatures combined with snow and ice in late winter, cows in the Minimal and Creep treatments received 392 lb DDGS/cow over the grazing season compared to 948 lb DDGS/cow in DDGS treatment. As a result, there were no significant differences in cow BW or BCS between treatments throughout the winter grazing season. No significant differences were found in forage mass or the concentrations of CP, ADF, NDF, ADIN, or IVDMD of pasture samples collected before or during winter grazing between treatments. Results imply that creep feeding a corn-soy hull pellet will increase calf body weight gains. However, neither creep feeding calves nor supplementing DDGS to cows to maintain a condition score of 5 affects body weights or condition scores of cows grazing stockpiled forages in comparison to cows that are supplemented only when necessary because of excessive cold or ice