The Silent Aircraft is in the form of a flying wing with a large wing planform and a propulsion system that is embedded in the rear of the airframe with intakes on the upper surface of the wing. Thus a large part of t...
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ISBN:
(纸本)1563478099
The Silent Aircraft is in the form of a flying wing with a large wing planform and a propulsion system that is embedded in the rear of the airframe with intakes on the upper surface of the wing. Thus a large part of the forward-propagating noise from the intake ducts is expected to be shielded from observers on the ground by the wing. Acoustic shielding effects can be calculated by solving an external acoustic scattering problem for a moving aircraft. In this paper, acoustic shielding effects of the Silent Aircraft airframe are quantified by a ray-tracing method. The dominant frequencies from the noise spectrum of the engines are sufficiently high for ray theory to yield accurate results. It is shown that for low-Mach number homentropic flows, a condition satisfied approximately by the Silent Aircraft during take-off and approach, the acoustic rays propagate in straight lines. Thus, from Fermat's principle it is clear that classical Geometrical Optics and Geometrical Theory of Diffraction solutions are applicable to this moving-body problem as well. The total amount of acoustic shielding at an observer located in the shadow region is calculated by adding the contributions from all the diffracted rays (edge-diffracted and creeping rays) and then subtracting the result from the incident field without the airframe. Experiments on a model-scale geometry have been conducted in an anechoic chamber to test the applicability of the ray-tracing technique. The three-dimensional ray-tracing solver is validated by comparing the numerical solution with analytical high-frequency asymptotic solutions for canonical shapes.
Despite the extensive work on human-computer interaction regarding methods of involving users and designing for high degrees of usability, there is surprisingly little published on how procurer organizations understan...
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Despite the extensive work on human-computer interaction regarding methods of involving users and designing for high degrees of usability, there is surprisingly little published on how procurer organizations understand, reason about, and require usability. This study focuses on how one taxi company dealt with usability requirements when procuring a new dispatch system. We have conducted ten interviews with various stakeholders in the company and analyzed related documentation in order to discover the process. The case shows how the concept of usability matured during over time. The taxi company dealt with requirement elicitation by developing prototypes in small reference groups. They did no formal analysis of the operators' cooperation with each other at the operator central, but they did include experienced users, which created implicit scenarios. The supplier company did not focus on the efficiency of the operators or, for that matter, the cooperative demands of the operator central in their original design, which became evident when the procurer organization requested a redesign that emphasized user tasks. This indicates, on one hand, the extent to which procurers must understand usability and cooperation to procure good systems design and, on the other hand, the extent to which designers must understand business and activity processes in order to design good systems.
Understanding and interpreting dynamic scenes and activities is a very challenging problem. In this paper we present a system capable of learning robot tasks from demonstration. Classical robot task programming requir...
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Object recognition and pose estimation are of significant importance for robotic visual servoing, manipulation and grasping tasks. Traditionally, contour and shape based methods have been considered as most adequate f...
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We present a multidisciplinary scientific analysis combining aerodynamics, flight mechanics and electromagnetics aiming at the design of a new marine distress signaling device. We show how computational fluid dynamics...
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ISBN:
(纸本)0933957343
We present a multidisciplinary scientific analysis combining aerodynamics, flight mechanics and electromagnetics aiming at the design of a new marine distress signaling device. We show how computational fluid dynamics (CFD) and computational electromagnetics (CEM) techniques have been used to assist In the design of both the flight characteristics and the radar performance of the device, as well as how its radar signature compares to popular radar reflectors used on yachts and sailboats.
We describe several approaches for using prosodic features of speech and audio localization to control interactive applications. This information can be applied to parameter control, as well as to speech disambiguatio...
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We describe several approaches for using prosodic features of speech and audio localization to control interactive applications. This information can be applied to parameter control, as well as to speech disambiguation. We discuss how characteristics of spoken sentences can be exploited in the user interface;for example, by considering the speed with which a sentence is spoken and the presence of extraneous utterances. We also show how coarse audio localization can be used for low-fidelity gesture tracking, by inferring the speaker's head position.
This paper describes a new way of visualizing threaded discussion forums on compact displays. The technique uses squarified treemaps to render the threads in discussion forums as colored rectangles, thereby using 100%...
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ISBN:
(纸本)1595930027
This paper describes a new way of visualizing threaded discussion forums on compact displays. The technique uses squarified treemaps to render the threads in discussion forums as colored rectangles, thereby using 100% of the limited screen space. We conducted a preliminary user study, which compared the treemap version and a traditional text based tree interface. This showed that the contents of the discussion forum were easily grasped when using a treemap, even though there were in excess of one hundred threads. In particular our technique showed a significant improvement in time for finding the largest and most active threads. Overall, it was shown that the benefits derived from using treemaps on desktop computers are still valid for small screens.
A protocol is given to take an ElGamal ciphertext encrypted under the key of one distributed service and produce the corresponding ciphertext encrypted under the key of another distributed service, but without the pla...
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