Atmospheric turbulence in phase-referenced and wide-field interferometric images: Application to the SKA

Phase referencing is a standard calibration procedure in radio interferometry. It allows to detect weak sources by using quasi-simultaneous observations of closeby sources acting as calibrators. Therefore, it is assumed that, for each antenna, the optical paths of the signals from both sources are similar. However, atmospheric turbulence may introduce strong differences in the optical paths of the signals and affect, or even waste, phase referencing for cases of relatively large calibrator-to-target separations and/or bad weather. The situation is similar in wide-field observations, since the random deformations of the images, mostly caused by atmospheric turbulence, have essentially the same origin as the random astrometric variations of phase-referenced sources with respect to the phase center of their calibrators. In this paper, we present the results of a Monte Carlo study of the astrometric precision and sensitivity of an interferometric array (a realization of the Square Kilometre Array, SKA) in phase-referenced and wide-field observations. These simulations can be extrapolated to other arrays by applying the corresponding corrections. We consider several effects from the turbulent atmosphere (i.e., ionosphere and wet component of the troposphere) and also from the antenna receivers. We study the changes in dynamic range and astrometric precision as a function of observing frequency, source separation, and strength of the turbulence. We find that, for frequencies between 1 and 10 GHz, it is possible to obtain images with high fidelity, although the atmosphere strongly limits the sensitivity of the instrument compared to the case with no atmosphere. Outside this frequency window, the dynamic range of the images and the accuracy of the source positions decrease. [...] (Incomplete abstract. Please read manuscript.)Comment: 9 pages, 11 figures. Accepted for publication in A&A

Principios e interés de los test Bondad de Ajuste (GOF) para los modelos de captura–recaptura multiestado

Optimal goodness–of–fit procedures for multistate models are new. Drawing a parallel with the corresponding single–state procedures, we present their singularities and show how the overall test can be decomposed into interpretable components. All theoretical developments are illustrated with an application to the now classical study of movements of Canada geese between wintering sites. Through this application, we exemplify how the interpretable components give insight into the data, leading eventually to the choice of an appropriate general model but also sometimes to the invalidation of the multistate models as a whole. The method for computing a corrective overdispersion factor is then mentioned. We also take the opportunity to try to demystify some statistical notions like that of Minimal Sufficient Statistics by introducing them intuitively. We conclude that these tests should be considered an important part of the analysis itself, contributing in ways that the parametric modelling cannot always do to the understanding of the data.Los procedimientos óptimos de bondad de ajuste, aplicados a los modelos multiestado, son nuevos. Trazando un paralelismo con los correspondientes procesos de uniestado, presentamos sus articularidades y mostramos como el test general puede descomponerse en componentes susceptibles de ser interpretados. Todos los desarrollos teóricos están ilustrados con una aplicación del ya clásico estudio de los desplazamientos de la barnacla canadiense entre sus lugares de invernada. Mediante esta aplicación, presentamos un ejemplo de cómo los componentes susceptibles de ser interpretados nos proporcionan una idea de los datos que nos pueden llevar a la elección de un modelo general apropiado, pero también a veces a la invalidación de los modelos de multiestados en su conjunto. Se menciona entonces el método para calcular un factor de corrección de la sobredispersión. Aprovechamos esta ocasión para intentar también desmitificar algunas nociones estadísticas, como las Estadísticas Suficientes Mínimas, introduciéndolas intuitivamente. La conclusión es que estas pruebas deberían considerarse una parte importante del propio análisis, contribuyendo a la comprensión de los datos, de un modo que el modelaje paramétrico no siempre consigue

Designing end use components for additive manufacturing: navigating an emerging field

Despite much excitement, research and development, Additive Manufacturing (AM) as a series production process for end-use components and products is not yet widespread or considered mainstream. However, there is a clear potential for AM to form a viable alternative to many conventional manufacturing processes, especially in low to medium production volumes. A key enabler for this transformation is the capacity to design components and products that are both able to exploit AM capabilities and avoid its limitations. In recent years, many studies have explored the topic of Design for Additive Manufacturing (DfAM). This report presents an overview of the state of the art of this research area. A systematic review has been carried out to identify the most significant academic studies on the topic. The review resulted in 66 key resources being identified and critically reviewed. These resources have been reviewed and categorised using a generic model of the design process. This categorisation provides and easy and immediate way to map and navigate this emerging field. Consequently, five major research areas are presented: 1. Process planning 2. Detail design 3. Embodiment design 4. Conceptual design 5. Design processes In the discussion, these research areas are examined with the aim of highlighting shortcomings and providing future research directions

DESIGNING END USE COMPONENTS FOR ADDITIVE MANUFACTURING Exploring experiences, knowledge and information requirements

The primary aim of this study was to develop an understanding of the experience, the current knowledge regarding the design of end-user components for series production in additive manufacturing (AM) and the information needs of designers involved in designing end-user components for AM. To achieve this, the survey intended to uncover the following aspects of the topic: 1. If and how frequently AM technologies are used by designers for series production of end-user components 2. To what extend designers have had experience of designing end-user components for AM 3. Which aspects are important when designing end-user components for additive 4. Why designers have or not have designed end-user components for series production in AM 5. How designers have learned how to design for AM and which resources they have used 6. What designers would like to know about Design for AM 7. How they prefer this information to be conveye

A framework for mapping design for additive manufacturing knowledge for industrial and product design

© 2018, © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. Design for Additive Manufacturing (DfAM) is a growing field of enquiry. Over the past few years, the scientific community has begun to explore this topic to provide a basis for supporting professional design practice. However, current knowledge is still largely fragmented, difficult to access and inconsistent in language and presentation. This paper seeks to collate and organise this dispersed but growing body of knowledge, using a single and coherent conceptual framework. The framework is based on a generic design process model and consists of five parts: Conceptual design, Embodiment design, Detail design and Process planning and Process selection. 81 articles on DfAM are mapped onto the framework to provide, for the first time, a clear summary of the state of the art across the whole design process. Nine directions for the future of DfAM research are then proposed

Transmission measurement at 10.6 microns of Te2As3Se5 rib-waveguides on As2S3 substrate

The feasibility of chalcogenide rib waveguides working at lambda = 10.6 microns has been demonstrated. The waveguides comprised a several microns thick Te2As3Se5 film deposited by thermal evaporation on a polished As2S3 glass substrate and further etched by physical etching in Ar or CF4/O2 atmosphere. Output images at 10.6 microns and some propagation losses roughly estimated at 10dB/cm proved that the obtained structures behaved as channel waveguides with a good lateral confinement of the light. The work opens the doors to the realisation of components able to work in the mid and thermal infrared up to 20 microns and even more.Comment: The following article appeared in Vigreux-Bercovici et al., Appl. Phys. Lett. 90, 011110 (2007) and may be found at http://link.aip.org/link/?apl/90/01111

Investigation of design for additive manufacturing in professional design practice

© 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. Additive Manufacturing (AM) technologies are widely adopted in design practice for prototyping. However, the extent to which practitioners are knowledgeable and experienced in designing components for series production using AM remains poorly understood. This study presents the results of an online survey aimed at uncovering this emerging design activity, with additional evidence provided by semi-structured interviews with 18 designers. One hundred ten practising designers responded. The majority of the respondents remain sceptical about the potential for AM as a process for series production, citing cost and technical capabilities as key barriers. Only 23 reported experience in designing components for series production using AM, with the majority of these designing parts to be produced from plastic. The survey revealed that these designers have developed their own ‘design rules’ based primarily on personal experience. These rules, however, tended to focus on ensuring ‘printability’ and did not provide support for taking advantage of the unique capabilities of AM processes. The designers tended to treat AM processes as a uniform set of production processes, and so the design rules they used were generic and not directed to the capabilities of specific AM processes