No abstract

No abstract

Coastal storms are the primary drivers of coastal change, but submerged areas historically have been difficult to map and consequently to document change. Hurricane Sandy had a dramatic impact along coastal areas in proximity to landfall in late October 2012 and those impacts have been well-documented in terrestrial coastal settings, however, due to the lack of data on submerged marine habitats similar studies have been limited. One of the motivations for this study was to provide park managers with a baseline inventory of submerged marine habitats to measure change during future storm events. A three-year study to map submerged habitats in Cape Cod National Seashore was recently completed. This was one of four contemporaneous studies that developed maps of submerged shallow water marine habitat in and around coastal national parks along the east coast of the United States. These four projects used similar methods of data collection, processing and analysis for the production of benthic habitat maps. Data from a phase-measuring sidescan sonar, bottom grab samples, seismic reflection profiling, and sediment coring we all used to develop submerged marine habitat maps using the Coastal and Marine Ecological Classification Standards (CMECS) in Cape Cod National Seashore. Over 76 vessel-based acoustic surveys were conducted in extreme shallow water, across four embayments from 2014-2016. Sidescan sonar imagery totaling 83.1 km2 were collected and within that area 61.3 square kilometres of collocated bathymetric data were collected with a mean depth of 4.6 m. Bottom grab samples (n = 476) and ancillary data were collected, macroinvertebrates were identified and used within the CMECS framework along with the geophysical and coring data to develop final habitat maps.

The present paper focuses on directional solidification processes for photovoltaic silicon purification. The use of a mechanical stirrer in the melt to enhance impurity segregation is investigated through numerical simulations. The 3D forced convection flow is resolved in a transient regime thanks to a sliding mesh approach. The hydrodynamic model is coupled to a solute transport simulation in a quasi-steady approximation (i.e. with constant liquid height). Velocity measurements are performed by Particle Image Velocimetry on a water model in order to validate hydrodynamic simulations. Numerical results show that an efficient segregation can be achieved, even for high solidification rates, thanks to mechanical stirring. The numerical model provides meaningful insights for process optimization as it correlates the impurity repartition on the solidification front to the stirring parameters. Finally, the numerical segregation results are compared to an analytical model of the solute boundary layer. It is found that the analytical model provides a good estimate of the mean segregation regime from an hydrodynamic simulation of the forced convection flow, which makes it a useful tool for process design.

No abstract

No abstract

No abstract

Coastal areas have traditionally been difficult locations to collect consistent, high-resolution bathymetric data via vessel-based acoustic surveys. The use of phase-measuring sidescan sonar is becoming more prevalent, particularly in shallow (< 20 m) coastal waters. Instruments used in the field over the last decade by the lead author are discussed here. This work is intended to serve as an introduction to the coastal scientist interested in the operation, use, and data sets associated with these instruments. Hydrographers unfamiliar with phase-measuring sidescan sonar will also benefit from insights regarding survey planning, data acquisition, and processing. These instruments collect co-located sidescan backscatter and swath bathymetry. The effective bathymetric swath widths can be 2 to 3 times that of multibeam echosounders making phase-measuring sidescan sonars ideal for shallow water mapping operations. These large effective swath widths offset the high levels of noise and processing needed in these bathymetric data sets relative to multibeam data. The sidescan backscatter and bathymetric data sets can be used individually, but the co-location allows for uses and analyses not feasible with other data sets. These instruments are well-suited to collect data for a suite of seafloor mapping projects and science-based investigations. Examples from a wide range of projects are detailed here for the shallow water mapping community and the multi-disciplinary groups who may benefit from the data and insights presented here.