Optimal low-thrust trajectories to asteroids through an algorithm based on differential dynamic programming

In this paper an optimisation algorithm based on Differential Dynamic Programming is applied to the design of rendezvous and fly-by trajectories to near Earth objects. Differential dynamic programming is a successive approximation technique that computes a feedback control law in correspondence of a fixed number of decision times. In this way the high dimensional problem characteristic of low-thrust optimisation is reduced into a series of small dimensional problems. The proposed method exploits the stage-wise approach to incorporate an adaptive refinement of the discretisation mesh within the optimisation process. A particular interpolation technique was used to preserve the feedback nature of the control law, thus improving robustness against some approximation errors introduced during the adaptation process. The algorithm implements global variations of the control law, which ensure a further increase in robustness. The results presented show how the proposed approach is capable of fully exploiting the multi-body dynamics of the problem; in fact, in one of the study cases, a fly-by of the Earth is scheduled, which was not included in the first guess solution

Towards good practice guidelines for the contour method of residual stress measurement

Accurate measurement of residual stress in metallic components using the contour method relies on the achievement of a good quality cut, on the appropriate measurement of the deformed cut surface and on the robust analysis of the measured data. There is currently no published standard or code of practice for the contour method. As a first step towards such a standard, this study draws on research investigations addressing the three main steps in the method: how best to cut the specimens; how to measure the deformation contour of the cut surface; and how to analyse the data. Good practice guidance is provided throughout the text accompanied by more detailed observations and advice tabulated in Appendi

Magnetic resonance imaging biomarkers for chronic kidney disease: a position paper from the European Cooperation in Science and Technology Action PARENCHIMA

Functional renal magnetic resonance imaging (MRI) has seen a number of recent advances, and techniques are now available that can generate quantitative imaging biomarkers with the potential to improve the management of kidney disease. Such biomarkers are sensitive to changes in renal blood flow, tissue perfusion, oxygenation and microstructure (including inflammation and fibrosis), processes that are important in a range of renal diseases including chronic kidney disease. However, several challenges remain to move these techniques towards clinical adoption, from technical validation through biological and clinical validation, to demonstration of cost-effectiveness and regulatory qualification. To address these challenges, the European Cooperation in Science and Technology Action PARENCHIMA was initiated in early 2017. PARENCHIMA is a multidisciplinary pan-European network with an overarching aim of eliminating the main barriers to the broader evaluation, commercial exploitation and clinical use of renal MRI biomarkers. This position paper lays out PARENCHIMA’s vision on key clinical questions that MRI must address to become more widely used in patients with kidney disease, first within research settings and ultimately in clinical practice. We then present a series of practical recommendations to accelerate the study and translation of these techniques

Academie of periferie?: waardering door de leerling.

Inleiding: De opleiding van basisartsen en medisch specialisten vindt zowel in universitaire klinieken als perifere opleidingsziekenhuizen plaats. In dit artikel is onderzocht of er een verschil bestaat tussen academische en niet-academische centra in de waardering van onderwijsitems. Methode: Hiertoe zijn twee groepen onderzocht. Allereerst de co-assistenten (n=90) die middels een enquete hun mening gaven over het ervaren onderwijsklimaat tijdens hun co-schap gynaecologie en verloskunde. Daarnaast is (voormalige) agio's verloskunde en gynaecologie (n=326) gevraagd waar zij de meeste vaardigheden en kennis hebben opgedaan. Resultaten: De co-assistenten vonden het onderwijsklimaat in de periferie beter dan in de academie (p<0.05). Agio's en pas afgestudeerde gynaecologen deden vaardigheden en kennis het meest op in niet-academische ziekenhuizen (p<0.05). Discussie en conclusie: Oorzaken voor deze uitkomsten worden gezocht in (1) de beperkte prioriteit die de medische opleiding in academische ziekenhuizen krijgt en in (2) veranderende patiëntenstromen die het onderwijsklimaat benadelen. Er wordt voor gepleit om academische en niet-academische ziekenhuizen verder te laten integreren om de verschillende taken als onderwijs en onderzoek optimaal te laten vervullen. Daarbij is een herwaardering nodig van diegenen die zich sterk inspannen ten behoeve van de medische opleiding. (aut.ref.