Bulent Uludag, DDS, PhD/Serdar Polat, DDS, PhD/Volkan Sahin, DDS, PhD/Ali Alper ?omut, DDS, PhD: Purpose: The aim of this study was to evaluate the effects of different implant angulations and attachment configurations on the retentive forces of locator attachment?retained overdentures over a simulated time period of 6 months. Materials and Methods: Two acrylic resin models (models 1 and 2) were fabricated to represent an edentulous mandible. In model 1, the midline implant (in the central region) was vertical and the other two implants (in the canine regions) were 20 degrees divergent from the midline, reaching a total divergence of 40 degrees. In model 2, all three implants were vertically oriented, perpendicular to the occlusal plane and parallel to each other. Three-point vertical pull-out forces were employed in a universal testing machine at a constant crosshead speed of 50 mm/min after overdenture construction and a simulation of 6 months of repeated insertions/removals of the overdenture. Locator attachments with different male combinations and bar and clip attachments were tested in model 1. Clear locator attachments and bar and clip attachments were tested in model 2 and served as controls. Results: The initial retentive forces of all attachments in both models ranged from 26.58 to 62.05 N, whereas the initial retentive forces of the attachments for only model 1 ranged from 49.58 to 62.05 N. The highest retention value was recorded for clear green locator attachments and the lowest for hader bar yellow clip attachments. Locator attachments showed higher retention values than hader bar yellow clip attachments. Conclusion: All attachment systems demonstrated a decrease in retention over time. Locator attachments provided better retention than hader bar yellow clip attachments. The highest retention values were obtained when green male locators were used in combination with male attachments.

Wastewater formed on ships is divided into blackwater and graywater. While blackwater refers to wastewater from toilets, graywater defines wastewater from sinks, laundry and restaurants. Even though some treatments are applied onboard before discharge, wastewater contains significant amounts of fecal bacteria, heavy metals, etc., in excess of water quality standards. Dilution is a secondary natural treatment in the ship-wake region, which occurs after wastewater discharging. According to the Environmental Protection Agency (EPA), the natural treatment process is quantified by dilution factor, which is strongly dependent on vessel width, draft, speed and wastewater discharge rate. In this study, an Artificial Neural Network (ANN) model linked with the main ship parameters was developed to estimate the dilution factors while the ship is in the preliminary design stage. Gross ton, deadweight ton, passenger number, freeboard, engine power, propeller number and block coefficient values of 1041 large cruise ships were used to estimate the likely dilution factors. The best ANN estimation model was determined by Root Mean Square Error (RMSE) and Mean Absolute Error (MAE) methods. A decision tree was created for the results and the most important parameters affecting the dilution factors were determined. The main ship dimensions are needed for the dilution factor formulation of EPA whereas in the model created in this study only the gross ton or engine power of the ship is sufficient to estimate the dilution. Moreover, this new model is also usable for the estimation of dilution factors even if the main dimensions of the ship are not known.

Ships, which are the essential elements of maritime transportation, have an indispensable role in world freight and passenger transportation. Besides sea routes, the role played by ships in inland water transport is also very important. In addition to these important economic effects, ships are also a major pollutant source. These emissions have negative effects on human health, cities, and the environment, as well as causing atmospheric pollution. Lake Van is Turkey's largest inland lake, with an area of ​​3,713 km2, and is an important inland waterway, with an active ferry network operating between Van and Tatvan-Bitlis. In this study, emission calculations of these ferries operating in Lake Van were carried out; it was aimed to develop an emission inventory for ship-related air pollution on Lake Van. Additionally, the environmental (social) costs of these emissions were estimated to assess the total impacts. One year of ship operation data was used for the calculations, and the engine power method was preferred, according to the available data. According to the calculations, the ship-originated emission inventory on Lake Van was determined to be 36,140.54, 107.84, 29.15, 17.49, 990.95, and 11.66 t for CO2, SO2, CO, HC, NOx, and PM, respectively. The total environmental costs of these emissions were calculated to be 40,046,340 €. These results are important in terms of determining the environmental effects of transportation activities in Lake Van, which have not been studied before. Highlights The study covers the emission and environmental cost estimation of maritime transportation in Lake Van The total emissions are estimated at 37,297.63 t The total environmental cost is estimated at 40,046,340 € It is recommended that IMO regulations should strictly implemented in inland waters