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Effects of salt stress on interspecific competition between an invasive alien plant Oenothera biennis and three native species
Get PDFBiological invasions and soil salinization have become increasingly severe environmental problems under global change due to sea-level rise and poor soil management. Invasive species can often outcompete native species, but few studies focus on whether invasive alien species are always superior competitors under increasing stressors. We grew an invasive grass species, Oenothera biennis L., and three native grass species (Artemisia argyi Lévl. et Vant., Chenopodium album L., and Inula japonica Thunb.) as a monoculture (two seedlings of each species) or mixture (one seedling of O. biennis and one native species seedling) under three levels of salt treatments (0, 1, and 2 g/kg NaCl) in a greenhouse. We found that invasive O. biennis exhibited greater performance over native C. album and I. japonica, but lower performance compared to A. argyi, regardless of the soil salinity. However, salinity did not significantly affect the relative dominance of O. biennis. Interspecific competition enhanced the growth of O. biennis and inhibited the growth of I. japonica. Although O. biennis seedlings always had growth dominance over C. album seedlings, C. album was not affected by O. biennis at any salt level. At high salt levels, O. biennis inhibited the growth of A. argyi, while A. argyi did not affect the growth of O. biennis. Salt alleviated the competitive effect of O. biennis on I. japonica but did not mitigate the competition between O. biennis and the other two native species. Therefore, our study provides evidence for a better understanding of the invasive mechanisms of alien species under various salinity conditions
Ambient Temperature Phase Change Launcher
Get PDFThe Naval Undersea Warfare Center, or NUWC, has tasked Team 16 with analyzing a way to vertically launch a columnar payload underwater through the use of a phase change of a liquid to a gas. The system must harness the potential energy created from a pressurized gas being stored in a liquid phase then released to undergo a phase change to launch a payload through water.
NUWC has given Team 16 design requirements that include that the pressurized chamber must be less than 25% of the volume of the launch tube, the acceleration of the payload must be less than 8g at launch, and that the length of the payload must be seven to eight times the diameter of the payload. The team combined these design requirements with customer requirements to create the design specifications for this project. The team then undertook a design process which was a lengthy process of deriving over ninety possible designs. These designs were then narrowed down to three realistic contenders before a final design was chosen. Further testing was conducted to prove its viability. The final design chosen demonstrated the ability for a rupture disc to be deployed in a scenario outside its originally intended purpose.
During the spring semester, the system was scaled up by a factor of ten to operate at the pressures needed to store liquid carbon dioxide. The team designed the final launcher using carbon steel and aluminum. Generally speaking, the team used the proof of concept design but manufactured it using stronger materials. Dry ice was implemented to change phases and energize our payload by bursting an aluminum plate. A heating element was used to trigger the launch. The team elected to conduct underwater testing using only a submerged launch tube and left the remaining components outside of the closed system. The payload design was finalized and utilized a thread system so that items could be added/removed from the interior of the payload
iTherm by ASME: 3D Printed Heatsink Competition
Get PDFThis paper details the process of designing of a complex lattice geometry through CAD and the development of an additively manufactured heatsink by Team 04; this design accomplishes the goal of developing a heat sink that dissipates heat efficiently for a competition hosted by The American Society of Mechanical Engineers and General Electric. An aluminum heat sink which needs to be designed to be as light as possible while fulfilling other requirements such as: efficiency, price, size, amongst other factors. To do this, the following protocol was followed. First a literature search was conducted to learn more about the topic, followed by a meeting with the project’s faculty advisor, Professor Ashutosh Giri, to further clarify the goal and requirements of the project. Next, key steps in the design process were taken, including defining the problem, conducting a patent search, producing design concepts, Pugh analyses and a QFD analysis, analytical analyses, and producing a model. All of which led up to a proof of concept, and finally, a redesign. In this report, the steps to design, model, and test a functional free convection heat sink
Planktic foraminifera iodine/calcium ratios from plankton tows
No full textPlanktic foraminifera test iodine to calcium ratios represent an emerging proxy method to assess subsurface seawater oxygenation states. Several core-top studies show lower planktic foraminifera I/Ca in locations with oxygen depleted subsurface waters compared to well oxygenated environments. The reasoning behind this trend is that only the oxidized species of iodine, iodate, is incorporated in foraminiferal calcite. The I/Ca of foraminiferal calcite is thought to reflect iodate contents in seawater. To test this hypothesis, we compare planktic foraminifera I/Ca ratios, obtained from plankton tows, with published and new seawater iodate concentrations from 1) the Eastern North Pacific with extensive oxygen depletion, 2) the Benguela Current System with moderately depleted oxygen concentrations, and 3) the well oxygenated North and South Atlantic. We find the lowest I/Ca ratios (0.07 µmol/mol) in planktic foraminifera retrieved from the Eastern North Pacific, and higher values for samples (up to 0.72 µmol/mol) obtained from the Benguela Current System and North and South Atlantic. The I/Ca ratios of plankton tow foraminifera from environments with well oxygenated subsurface waters, however, are an order of magnitude lower compared to core-tops from similarly well-oxygenated regions. This would suggest that planktic foraminifera gain iodine post-mortem, either when sinking through the water column, or during burial
An anchoring system for supporting platforms for wind energy devices
No full textThis paper presents data from an initial development stage of an \u27umbrella anchor\u27 concept. The anchor can be pushed into a sand deposit in a folded arrangement to reduce installation loads. When a pull-out load is applied to the mooring line, the anchor deploys to create a large embedded plate anchor. Physical modelling was carried out in a saturated sand bed with the anchor installed at depths of up to 1.6 m and loaded vertically. During installation, liquefaction was generated at the tip of the anchor to reduce the penetration resistance. This enabled the anchor to be installed quickly and accurately to a target depth. The anchor could provide pull-out resistances comparable to an anchor that has been wished-in-place at similar depths. The observed behaviour provided encouraging preliminary results and suggests that, with further development and analysis, the concept could potentially be used for commercial applications
Pullout Capacity of Single and Biwing Anchors in a Soft Clay Deposit: Model Investigation in a Centrifuge and FEM Predictions
No full textOne of the ways to install plate anchors in deep seabed is to drop the anchor system from the sea level and allow it to initially embed in the seabed under its own weight. Further dragging would cause the anchor to rotate and embed further into the seabed. There could be difficulties of getting the anchor plate horizontal or mooring line to be perpendicular to the plate where the maximum pullout capacity could be achieved. As part of the investigations, various aspects of the plate performance were examined through centrifuge testing in which the plate orientation and pullout angles were varied. It was presumed that dynamic stability of the anchor (during field installation) can be achieved by having the plate in biwing configuration. Therefore, the performance of the biwing anchors having different spacing between the plates was also examined in the centrifuge testing program and the findings were compared with predictions obtained through finite-element modeling (FEM). Both pullout directions and the plate angles considerably influenced the pullout capacity factors. The comparison between the predicted pullout capacity using FEM and measured pullout capacity for biwing anchors at shallow embedment depths was excellent. However, the FEM-predicted pullout capacity was noticeably lower than the measured ones for deep anchors. Pullout capacity of biwing anchors at shallow embedment depth increased as the spacing between the plates S increased from 0 to 0.5B. However, there appears to be a slight reduction in the performance in deep embedment anchors. This is also reflected in FEM findings
Simple Modifications to a Direct Shear Device to Perform Constant Normal Stiffness (CNS) Tests
No full textThis paper describes a simple approach to modify a direct shear test device to perform interface shear tests under constant normal stiffness (CNS) conditions. There is continued interest in the use of piles and pile anchors for both fixed and floating offshore wind structures, particularly in the sandy soils along the East Coast of the United States. Design analyses and modeling may require CNS testing, which closely represents the boundary conditions near the interface of the pile during axial monotonic and cyclic loading. The simple and economical modifications allow for the testing of any pile material-sand interface by mechanically maintaining constant normal stiffness conditions on the sample during shear
Structural instrumentation and monitoring of the Block Island Offshore Wind Farm
No full textThis work presents the design and installation of a continuous monitoring system for one of the offshore wind turbines in the Block Island Wind Farm, which is located 6.1 km off the coast of Block Island in Rhode Island, USA. The instrumentation plan includes wired and wireless accelerometers, strain gauges, and inclinometers. Considerations for the instrumentation design are discussed, including the type, number and location of sensors, as well as some of the challenges in the installation of sensors. The process of transferring data, samples of collected data, automated system identification and some preliminary results are presented
Delineating bedrock topography with geophysical techniques: An implication for groundwater mapping
No full textBedrock topography delineation is essential for shallow groundwater mapping because the bedrock surface is the lower boundary of the unconsolidated aquifer system and is difficult to map if covered by thick surficial deposits. Non-invasive geophysical techniques are suitable tools for quantifying the depth to bedrock at a single point location or the bedrock topography using an interpolation between multiple measurements, borings, outcrops, and knowledge of the local bedrock\u27s brittle and ductile structure. In this study, first, we developed a high-resolution bedrock topography map for the southern coast of Rhode Island, USA, with a wide range of available lithological data. Second, we employed the Horizontal to Vertical Spectral Ratio (HVSR) seismic method to develop a power-law regression between the resonance frequency and the depth to bedrock, and we demonstrated statistical techniques to refine the relationship. Like in most other formerly glaciated regions worldwide, the surficial deposits are glacial outwash and till. It was found that the predictive performance of HVSR was better for glacial outwash than till mixed outwash. In addition, we highlighted the importance of the HVSR technique in interpreting the electrical resistivity profiles for groundwater mapping in both inland and coastal aquifers. Though the quantitative results are site-specific, the approach and insights are generalizable to any unconfined aquifers