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The history of stealth is fairly recent but has experienced a significant development over the past decades leading to the creation of several generations of stealth aircrafts and notably the Lockheed F22 and the F22 Raptor.Stealth aircrafts are conceived in order to deflect or absorb waves and send back to the radar a very attenuated signal. Stealth is based upon several basic principles linked to existing electromagnetic phenomena. The radar equivalent surface of the object must be reduced to the minimum so that it is detected by radars as late as possible.The design of a stealth aircraft is subjected to rules in terms of shape, cavities and choice of absorbing materials. Since these developments, stealth has been successfully applied to missiles, drones and warships.
Artificial intelligence (AI) has experienced accelerated growth in the digital media field since the 2015s. This article first provides a reminder of the principles, components and techniques of artificial intelligence, in particular machine learning, and deep learning with neural networks. It then proposes a sample of AI applications developed in the field of images in photography, for old films, and in video. In the field of sounds, the article presents some examples related to the automatic processing of speech, 3D audio and music.
Unlike other studies carried out in this field, the study of the acoustics of rooms cannot be mathematically modelled in order to describe the propagation of sound. This article presents the linearization process of a complex set of variables, which, unlike in traditional models, does not involve prioritization or traditional parameterization. It includes a methodological scheme involving six proposals concerning the virtual distribution of sources, the search for a compromise criterion between clarity and homogeneity, the choice of a frequency band, the determination of the opening angle of sources and the delineation of the listening plane. The implementation of the model is analyzed in the case where sources are predetermined and in the case where only the site is known.
Room acoustics is a discipline which requires the implementation of multiple areas of knowledge, by a number of condition variables on a given configuration. This article provides a detailed and systematic approach. After an advanced study on possible difficulties (major defects, coupling, etc.) as well as the calculation of the duration of reverberation and sound levels, the article moves on to the systematic measurement phase before returning to the core issue which is modeling. The fourth phase includes the accomplishments of the project making comparison between the prevision and the actual values and validation of the models. The final phase looks at the opportunities of publishing the results.
The acoustic study of a room is carried out via an approach by models. This does not only involve acoustic knowledge. In this article, this approach is illustrated by three examples. The first one, a simple optimization attempt based on a traditional model, is an intermediary stage between the systematic approach and the linearized approach. The second one, based on a simple comparison of two calculation formulae of a reverberation length, is a typical bifurcation scheme involved in most models. The third example illustrates how the failure of a traditional model can be addressed in order to achieve suitable adequacy between measurements and predicted values.
Woodworking and carpentry are high-risk occupations owing to the extensive use of stationary wood-cutting machinery. Accidents or injuries are critical. Use of a Virtual Learning Environment (VLE) can help to secure motion skills and ensure safety of the worker. This article first presents VLE, with comparative examples and their application in motion skills learning. Specific requirements for wood-cutting machinery are developed, with presentation of our solution suite, developed in partnership with the French Vocational Institute (AFPA).
This article is the first of a series of three about immersive audiovisual systems. It first defines their components: the omnidirectional content (360° video and 3D audio), the continuum from reality to virtuality and its various degrees with the immersion and interactivity factors, the user interfaces (visiocasque, binaural...). In a second part it details the functions and techniques: captation, processing, coding and formatting, delivery and use. The last part specifies the coding and formatting standards for delivery, in particular those of the MPEG-I Immersive Media suite (OMAF...).
This article describes the digital native “format” into which are converted sounds and pictures in our present media environment. The digital native format is the result of the discontinuous coded measurement of the analog values, continuous and proportional, generated by a microphone or a camera. These analog values correspond to the intensity of the sound or light vibrations perceived by our hearing and vision. This measurement, “digitization”, is specified by precise parameters, which are detailed in this article for each medium: audio, still pictures and video.
This article is the third and last one of a series of three about immersive audio-visual systems. It first describes the formats and standards needed to encode and format immersive media (360° video, 3D audio) for distribution. Two case studies illustrate on the one hand the streaming or downloading of 360° content, and on the other hand the association of 360° content and live TV. Then, the article presents a panorama of applications and use cases and describes the user interfaces required to "consume" immersive audio-visual experiences. Finally, it explains the factors of video and audio quality, as well as thoses of the quality of experience.
Scientific and technological advances in the field of virtual reality make it possible to create, evaluate, and disseminate interactive and immersive applications at low cost. Whether to simulate real-life situations and/or to enhance human capabilities, virtual reality is used currently in several fields. This article covers in particular its use in learning and training. It Starts with an introduction to virtual reality and the advantages of its use. Then, it presents how virtual learning environments are designed, and concludes with a study of concrete use cases.
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