Attitude Dynamics and Control of Solar Sails with Articulated Vanes

In this paper we develop a robust nonlinear algorithm for the attitude control of a solar sailcraft with M single degree-of-freedom articulated control vanes. A general attitude controller that tracks an admissible trajectory while rejecting disturbances such as torques due to center-of-mass to center-of-pressure offsets is applied to this problem. We then describe a methodology based on nonlinear programming to allocate the required control torques among the control vanes. A simplified allocation strategy is then applied to a solar sail with four articulated control vanes, and simulation results are given. The performance of the control algorithm and possible limitations of vane-only control are then discussed

Testing sodium borohydride as a fuel additive in internal combustion gasoline engine

Additives are added to conventional fuels to ensure complete combustion of fuels, increase engine performance and reduce harmful emissions from vehicles. Hydrogen and oxygen-containing fuel additives added to fossil-based internal combustion engine fuels improve the properties of the fuels and reduce vehicle-related emissions. Evaluation of mixed fuels created by adding different types of alcohol and nano-sized additives to motor fuels as an alternative fuel in motor vehicles is among the most researched scientific studies recently. In this study, alcohol-gasoline fuels (E5, M5), NaBH4-alcohol-gasoline fuels (ES5, MS5), and pure gasoline were tested in a gasoline engine. Fuels used in engine tests; E5 fuel (5% by volume ethanol 95% gasoline blend), M5 fuel (5% by volume methanol 95% gasoline blend), ES5 fuel (5% by volume NaBH4-ethanol solution 95% gasoline blend), MS5 fuel (5% by volume NaBH4-methanol solution 95% gasoline mixture) and pure gasoline. In the experiments, brake thermal efficiency, engine torque, specific fuel consumption, and exhaust gas temperature were measured and compared with pure gasoline. Compared to gasoline, the exhaust gas temperatures of all blended fuels decreased. On the other hand, there was an increase in engine torque values, except for ES5 fuel. At the same time, there was an increase in both specific fuel consumption and brake thermal efficiency. When the CO and HC emission values of the blended fuels are compared with the gasoline fuel values, the highest reduction in CO emissions occurred in ES5 blended fuel with 65.53%, while the highest decrease in HC emission was realized in E5 fuel with 19.09%. On the other hand, when NOx and CO2 emissions of E5, M5, ES5, MS5 mixed fuels are compared with gasoline, NOx emissions are 12.63%, 28.37%, 19.65%, respectively; decreased by 36.03% but CO2 emissions increased by 8.51%, 30.46%, 34.48%, 25.95% respectively. © 2022 Elsevier Lt

Dynamics of Drag Free Formations in Earth Orbit

In this paper the translational equations of motion of a formation of n spacecraft in Earth orbit, n(sub f) of which are drag-free spacecraft, are derived in a coordinate-free manner using the balance of linear momentum and direct tensor notation. A drag-free spacecraft consists of a spacecraft bus and a proof mass shielded from external disturbances in an internal cavity. By controlling the spacecraft so that the proof mass remains centered in the cavity, the spacecraft follows a purely gravitational orbit. The results described in this paper provide a first step toward coupling drag-free control technology with formation flying in order to mitigate the effect of differential aerodynamic drag on formation flying missions (e.g., Earth imaging applications) in low Earth orbit

Gnathic osteosarcomas, experience of four institutions from Turkey

Osteosarcoma is the most frequent primary gnathic sarcoma. Neither the etiology nor the variables effecting the prognosis are fully known due mostly to the rarity of gnathic osteosarcomas. To date a considerable number of clinicopathologic features have been suggested in the evaluation of gnathic osteosarcomas. Still there is a need to experience on several aspects of management. The aim of this study is to report a series of 33 cases of osteosarcoma involving either mandible or maxilla. The clinical, radiological and histopathological features of our cases have usually been non-specific and the most frequent provisional diagnosis were benign fibroosseous lesion, abnormal mass, giant cell granuloma and benign bone tumor. This non-specific presentation of osteosarcomas of the jaws is compatible with those reported previously. A combined clinical, radiological and pathological study is essential in arriving at the correct diagnosis