Unitary groups acting on Grassmannians associated with a quadratic extension of fields.

Let (V,H) be an anisotropic Hermitian space of finite dimension over the algebraic closure of a real closed field K. We determine the orbits of the group of isometries of (V,H) in the set of the K-subspaces of V

Piloted Simulation of Various Synthetic Vision Systems Terrain Portrayal and Guidance Symbology Concepts for Low Altitude En-Route Scenario

In support of the NASA Aviation Safety Program's Synthetic Vision Systems Project, a series of piloted simulations were conducted to explore and quantify the relationship between candidate Terrain Portrayal Concepts and Guidance Symbology Concepts, specific to General Aviation. The experiment scenario was based on a low altitude en route flight in Instrument Metrological Conditions in the central mountains of Alaska. A total of 18 general aviation pilots, with three levels of pilot experience, evaluated a test matrix of four terrain portrayal concepts and six guidance symbology concepts. Quantitative measures included various pilot/aircraft performance data, flight technical errors and flight control inputs. The qualitative measures included pilot comments and pilot responses to the structured questionnaires such as perceived workload, subjective situation awareness, pilot preferences, and the rare event recognition. There were statistically significant effects found from guidance symbology concepts and terrain portrayal concepts but no significant interactions between them. Lower flight technical errors and increased situation awareness were achieved using Synthetic Vision Systems displays, as compared to the baseline Pitch/Roll Flight Director and Blue Sky Brown Ground combination. Overall, those guidance symbology concepts that have both path based guidance cue and tunnel display performed better than the other guidance concepts

Fatigue crack propagation in 2195-T8 aluminium alloy plate

The paper deals with fatigue crack propagation in a 2195-T8 alloy plate. It is shown that fatigue resistance of this alloy is comparable to that of the classical 2xxx or 7xxx competitor alloys. This study highlights stress ratio effects on the fatigue behaviour at the threshold: the stress intensity factor range ΔKth decreases as R increases. The crack growth path, very sensitive to the texture of the plate, occurs in a crystallographic way, giving rise to strong deflection and zig-zag advance. The crack path provokes a mixed mode I and II fatigue fracture, and makes active crack retardation by the crack closure mechanism

Fatigue crack propagation in 2195-T8 aluminium alloy plate

The paper deals with fatigue crack propagation in a 2195-T8 alloy plate. It is shown that fatigue resistance of this alloy is comparable to that of the classical 2xxx or 7xxx competitor alloys. This study highlights stress ratio effects on the fatigue behaviour at the threshold: the stress intensity factor range ΔKth decreases as R increases. The crack growth path, very sensitive to the texture of the plate, occurs in a crystallographic way, giving rise to strong deflection and zig-zag advance. The crack path provokes a mixed mode I and II fatigue fracture, and makes active crack retardation by the crack closure mechanism

Una facciata che respira : il restauro del palazzo di Calle Larga 22. Marzo sede della Camera di Commercio di Venezia / [testi tratti da materiali forniti da Roberta Bartolone ... [et al.] ; fotografie a cura di Guido Cecere]

Il saggio ricostruisce le fasi di costruzione e successiva trasformazione della sede della Camera di Commercio di Venezia sulla base di documenti storici d'archivio