PLANT COMMUNITIES IN DYNAMIC SYSTEMS: HOW DISTURBANCE INFLUENCES COASTAL PLANT COMMUNITY STRUCTURE AND FUNCTION

As the climate continues to change it is difficult to predict how barrier island function will respond to global change drivers accompanying predicted climate change. Disturbance frequency and nutrient enrichment in coastal regions are drivers of plant community change that increase with climate change. Plant communities on barrier islands are not only tightly connected to barrier island function but are also some of the first communities affected by environmental change, making them a critical piece in understanding how current drivers of global change will impact the future of barrier islands. The objective of my dissertation was to observe and manipulate coastal plant communities at local and large-scales to inform community-level species and trait-based alterations caused by differences in response to disturbance and nutrient enrichment. My results indicate barrier island trait-based communities can vary over local spatial scales depending on overarching topography and historic disturbance response. There is scale dependency in relationships between dominant stability domains, barrier island elevation, and dune plant community structure. At large spatial scales, climatic differences among islands contributes more to dune community richness and composition than elevation differences. At local scales, impacts of elevation, island stability, and local ecological processes on dune plant communities comes into focus. I also show that nutrient enrichment accompanied by climate change significantly alters both trait-based and species community composition. Species composition, trait-based composition, and lifeform abundance all produce conflicting results in response to nutrient additions, but these complexities can be clarified with detailed trait and species analyses when used cooperatively

Effect of a prior stretch on the aging response of an Al-Cu-Li-Ag-Mg-Zr alloy

Recently, a family of Al-Cu-Li alloys containing minor amounts of Ag, Mg, and Zr and having desirable combinations of strength and toughness were developed. The Weldalite (trademark) alloys exhibit a unique characteristic in that with or without a prior stretch, they obtain significant strength-ductility combinations upon natural and artificial aging. The ultra-high strength (approximately 690 MPa yield strength) in the peak-aged tempers (T6 and T8) were primarily attributed to the extremely fine T(sub 1) (Al2CuLi) or T(sub 1)-type precipitates that occur in these alloys during artificial aging, whereas the significant natural aging response observed is attributed to strengthening from delta prime (Al3Li) and GP zones. In recent work, the aging behavior of an Al-Cu-Li-Ag-Mg alloy without a prior stretch was followed microstructurally from the T4 to the T6 condition. Commercial extrusions, rolled plates, and sheets of Al-Cu-Li alloys are typically subjected to a stretching operation before artificial aging to straighten the extrusions and, more importantly, introduce dislocations to simulate precipitation of strengthening phases such as T(sub 1) by providing relatively low-energy nucleation sites. The goals of this study are to examine the microstructure that evolves during aging of an alloy that was stretch after solution treatment and to compare the observations with those for the unstretched alloy

Evaluation of the microstructure of Al-Cu-Li-Ag-Mg Weldalite (tm) alloys, part 4

Weldalite (trademark) 049 is an Al-Cu-Li-Ag-Mg alloy designed to have ultrahigh strength and to serve in aerospace applications. The alloy displays significantly higher strength than competitive alloys in both naturally aged and artificially aged tempers. The strengthening phases in such tempers have been identified to, in part, explain the mechanical properties attained. In general, the alloy is strengthened by delta prime Al3Li and Guinier-Preston (GP) zones in the naturally aged tempers. In artificially aged tempers in slightly underaged conditions, strengthening is provided by several phases including GP zones, theta prime Al2Cu, S prime Al2CuMg, T(sub 1) Al2CuLi, and possibly a new phase. In the peak strength artificially aged tempers, T(sub 1) is the predominant strengthening phase

Topography and disturbance influence trait‐based composition and productivity of adjacent habitats in a coastal system

Coastal systems experience frequent disturbance and multiple environmental stressors over short spatial and temporal scales. Investigating functional traits in coastal systems has the potential to inform how variation in disturbance frequency and environmental variables influence differences in trait‐based community composition and ecosystem function. Our goals were to (1) quantify trait‐based communities on two barrier islands divergent in topography and long‐term disturbance response and (2) determine relationships between community trait‐based composition and ecosystem productivity. We hypothesized that locations documented with high disturbance would have habitats with similar environmental conditions and trait‐based communities, with the opposite relationship in low‐disturbance locations. Furthermore, we expected higher productivity and lower site‐to‐site variation with low disturbance. Functional traits, biomass, and environmental metrics (soil salinity, elevation, and distance to shoreline) were collected and analyzed for two habitat types (dune and swale) on two Virginia barrier islands. Our results show that trait‐based community composition differed among habitat types and was related to disturbance. Habitats exhibited more similarity on the high‐disturbance island in both trait‐based composition and environmental variables. Conversely, the low‐disturbance island habitats were more dissimilar. We found the habitat with the lowest disturbance had the highest ecosystem productivity and had trait‐based communities indicative of highly competitive environments, while the high‐disturbance trait‐based communities were influenced by traits that indicate rapid recovery and growth. Site‐to‐site variation was similar in all dune habitats but differed among inter‐island swale habitats that varied in disturbance. These results highlight the importance of incorporating trait‐based analyses when approaching questions about community structure and ecosystem productivity in disturbance‐mediated habitats, such as coastal systems

Re-entry vehicle shape for enhanced performance

A convex shell structure for enhanced aerodynamic performance and/or reduced heat transfer requirements for a space vehicle that re-enters an atmosphere. The structure has a fore-body, an aft-body, a longitudinal axis and a transverse cross sectional shape, projected on a plane containing the longitudinal axis, that includes: first and second linear segments, smoothly joined at a first end of each the first and second linear segments to an end of a third linear segment by respective first and second curvilinear segments; and a fourth linear segment, joined to a second end of each of the first and second segments by curvilinear segments, including first and second ellipses having unequal ellipse parameters. The cross sectional shape is non-symmetric about the longitudinal axis. The fourth linear segment can be replaced by a sum of one or more polynomials, trigonometric functions or other functions satisfying certain constraints

Emergent interactions influence functional traits and success of dune building ecosystem engineers

Stability of coastal systems are threatened by oceanic and atmospheric drivers of climate change. Sea-level rise compounded with increased frequency and intensity of storms emphasizes need for protection of inner island systems by dune formations. Dune building processes are affected by interactions between growth of ecosystem engineering dune grasses and environmental factors associated with disturbance such as sand burial and salt spray. Climate change may also cause latitudinal expansion of some species, resulting in emergence of competitive interactions that were previously absent. Topographic structure of coastlines, traditionally influenced by sand burial, could change as a result of competition emergence. My goal was to determine if species functional trait responses to common abiotic factors are altered by novel and current biotic interactions. I performed a multi-factorial greenhouse experiment by planting three common dune grasses (Ammophila breviligulata, Uniola paniculata, and Spartina patens) in different biotic combinations, using sand burial and salt spray as abiotic stressors. I hypothesized that biotic interactions will cause these dune grasses to shift functional trait responses to abiotic factors that are associated with dune building. I found that plants consistently decreased in biomass when buried. I also found that competition between A. breviligulata and U. paniculata negatively affected dune building function traits of A. breviligulata. This indicates that competition with U. paniculata could alter dune structure. In comparison A. breviligulata had a positive interaction with S. patens, which increased functional trait responses to abiotic stress. Last, we found that competitive intransitivity could occur between these species. My results can be used to make predictions on cross-scale consequences of novel competitive events. This experiment also provides evidence that consideration of local biotic interactions is important in understanding connections between plant level dynamics and large-scale landscape patterns in high stress environment

Use of the Recreation Opportunity Planning System to Inventory Recreation Opportunities of Arid Lands

Recreation opportunity planning, which is being adopted by some land management agencies for recreation input to land management planning, is reviewed for Its applicability to arid land situations* Particular attention is given to the Inventory and analysis phases of the system and to what we have learned about its Implementation during its development

Compression of Biological Networks using a Genetic Algorithm with Localized Merge

Network graphs appear in a number of important biological data problems, recording information relating to protein-protein interactions, gene regulation, transcription regulation and much more. These graphs are of such a significant size that they are impossible for a human to understand. Furthermore, the ever-expanding quantity of such information means that there are storage issues. To help address these issues, it is common for applications to compress nodes to form supernodes of similarly connected components. In previous graph compression studies it was noted that such supernodes often contain points from disparate parts of the graph. This study aims to correct this flaw by only allowing merges to occur within a local neighbourhood rather than across the entire graph. This restriction was found to not only produce more meaningful compressions, but also to reduce the overall distortion created by the compression for two out of three biological networks studied

Photon Diffusion in Microscale Solids

This paper presents a theoretical and experimental investigation of photon diffusion in highly absorbing microscale graphite. An Nd:YAG continuous wave (CW) laser is used to heat the graphite samples with thicknesses of 40 microns and 100 microns. Optical intensities of 10 kW/cm^2 and 20 kW/cm^2 are used in laser heating. The graphite samples are heated to temperatures of thousands of kelvins within milliseconds, which are recorded by a 2-color, high-speed pyrometer. To compare the observed temperatures, the differential equation of heat conduction is solved across the samples with proper initial and boundary conditions. In addition to lattice vibrations, photon diffusion is incorporated into the analytical model of thermal conductivity for solving the heat equation. The numerical simulations showed close matching between experiment and theory only when including the photon diffusion equations and existing material properties data found in the previously published works with no fitting constants. The results indicate that the commonly-overlooked mechanism of photon diffusion dominates the heat transfer of many microscale structures near their evaporation temperatures. In addition, the treatment explains the discrepancies between thermal conductivity measurements and theory that were previously described in the scientific literature.Comment: 8 pages, 7 figures, (N.B. there is a typo and minor correction in Table 1 and References in the online version of the journal, corrected and highlighted in this PDF

Experimental Line Parameters of the b^(1)Σ^(+)_g ← X^(3)Σ^(-)_g Band of Oxygen Isotopologues at 760 nm Using Frequency-Stabilized Cavity Ring-Down Spectroscopy

Positions, intensities, self-broadened widths, and collisional narrowing coefficients of the oxygen isotopologues ^(16)O^(18)O, ^(16)O^(17)O, ^(17)O^(18)O, and ^(18)O^(18)O have been measured for the b^(1)Σg + ← X^(3)Σg − (0,0) band using frequency-stabilized cavity ring-down spectroscopy. Line positions of 156 P-branch transitions were referenced against the hyperfine components of the ^(39)K D_1 (4s ^(2)S_(1/2) → 4p ^(2)P_(1/2)) and D_2 (4s ^(2)S_(1/2) → 4p ^(2)P_(3/2)) transitions, yielding precisions of ~0.00005 cm^(−1) and absolute accuracies of 0.00030 cm^(−1) or better. New excited b^(1)Σg + state molecular constants are reported for all four isotopologues. The measured line intensities of the ^(16)O^(18)O isotopologue are within 2% of the values currently assumed in molecular databases. However, the line intensities of the ^(16)O^(17)O isotopologue show a systematic, J-dependent offset between our results and the databases. Self-broadening half-widths for the various isotopologues are internally consistent to within 2%. This is the first comprehensive study of the line intensities and shapes for the ^(17)O^(18)O or ^(18)O_2 isotopologues of the b^(1)Σg + ← X^(3)Σg − (0,0) band of O_2. The ^(16)O_2, ^(16)O^(18)O, and ^(16)O^(17)O line parameters for the oxygen A-band have been extensively revised in the HITRAN 2008 database using results from the present study