1,721,040 research outputs found
Helicobacter pylori and gastric cancer: Both primary and secondary preventive measures are required
No full textAutonomous taxi operations: Algorithma for the solution of the routing problem
No full textIn past decades, airport ground operations have attracted researchers, with the aim of increasing airport
efficiency and reducing the environmental impact of airport operations. Airplane taxi operations have received
particular attention for their significant impact on the airport efficiency and pollutant emissions and on the
fuel cost for airlines. Alternative solutions have been proposed to the engine-on taxi procedures, including the
employment of autonomous vehicles to tow the aircraft between gates and runways. In order to be performed,
autonomous taxi procedures require precise planning and scheduling by means of sophisticated management
systems. At the base of these management systems, lie algorithms for the solution of the routing problem, which
provide feasible paths on the airport surface. Two different approaches can be used: compute the paths on the
fly, or pre-compute all the possible paths between all the pairs of starting/ending points on the airport grid and
store them in a database that is called when needed. In this paper, four different algorithms are implemented
and compared for the computation of paths on the fly: two Hopfield-type neural networks and two algorithms
based on graph theory. Furthermore, two algorithms for the generation of the path database are presented:
a modified version of the Breadth-first search and an implementation of the k-shortest paths algorithm. Each
taxi mission, performed by the tractors, consists of three different events, called phases: one central towing
phase, where the tractor tows the aircraft between gate and runway and two repositioning phases in which the
tractors move from its actual position to the airplane or from the airplane back to the depot
Gastric precancerous lesion follow up based on pathological evidence
No full textGastric precancerous lesio
Cellulite orbitaria in esiti di resezione cranio-facciale per osteoma orbito-etmoido-sinusale.
No full textAn unconventional adaptive flutter suppression actuation system: From modeling to experimentation
No full textThis paper contributes to the definition of an unconventional actuation system, intended specifically for slender/highly flexible wings' flutter suppression, and coupled with an adaptive control algorithm to handle post-flutter flight dynamics and uncertainties deriving from unpredictable degradation of the structural properties. The design and validation process of the novel actuation architecture is presented. It is based on a row of multiple small spoiler, located at fifteen percent of the mean aerodynamic chord and coordinated by a modified Model Reference Adaptive Control (MRAC) algorithm. The spoilers' concept design is optimized by Computational Fluid Dynamics (CFD) numerical simulation, afterwards realized and wind tunnel tested to derive the aerodynamic database by means of a six-axes force balance. The mathematical model has served to implement and validate the adaptive control algorithm for a wide range of condition. The modeled system is tested from on-design flutter speed and nominal structural stiffness to post-flutter speed and reduced structural stiffness through the analysis of the wing proper frequencies and phases, which has demonstrated to be very effective in testing the adaptivity of the control architecture. This approach proves the robustness of the proposed architecture before experimentation, which is performed through a custom-made wind tunnel apparatus. The two degree of freedom oscillations during flutter are successfully controlled in all conditions. This paper aims at defining a robust procedure for aeroelastic phenomena control system design, which employs a synergy of modeling, simulation and experimental approaches. Discussions and pertinent conclusions are outlined in the final section of the paper
Experimental investigations on high-lift wing stall control strategies with synthetic jet actuators
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