Suboptimal predictive control for satellite detumbling

Rate damping in the initial acquisition phase of a magnetically controlled small satellite is a big challenge for the control system. In this phase, the main difficulties are dynamic nonlinearities due to high body rates, time-varying control due to the change in Earths magnetic field, inherent underactuation, and constraints on available power. The control system is required to minimize the detumbling time with minimal use of onboard resources. In comparison to the existing control techniques used in the initial acquisition phase, predictive control can be considered a suitable choice for handling such conflicting objectives in the presence of constraints. In this work, performance of two existing nonlinear model predictive control schemes that guarantee closed-loop stability are analyzed. Nonlinear model predictive control gives improved performance by reducing the detumbling time compared to classical control techniques based on the rate of change of Earths magnetic field; however, the computational requirements are high. Furthermore, it is demonstrated that, when the body rates increase, the computational burden of nonlinear model predictive control to reach an optimal point becomes prohibitively large. For these situations, an algorithm is presented that allows early termination of the optimizer by imposing an additional constraint on the cost reduction. The early termination criteria of the optimizer can be chosen based on the available computational resources. The imposed cost reduction constraint also helps in further reducing the detumbling time. Extensive numerical simulations show that the presented algorithm works well in practice for a good range of initial body rates. Copyright © 2013 by the American Institute of Aeronautics and Astronautics, Inc

Embodied Practices - Looking From Small Places

“Embodied Practices – Looking From Small Places” is an edited transcript of a conversation between theatre and performance scholar Sruti Bala (University of Amsterdam) and sociologist, criminologist and anthropologist Dylan Kerrigan (University of Leicester) that took place as an online event in November 2020. Throughout their talk, Bala and Kerrigan engage with the legacy of Haitian anthropologist Michel-Rolph Trouillot. Specifically, they focus on his approach of looking from small units, such as small villages in Dominica, outwards to larger political structures such as global capitalism, social inequalities and the distribution of power. They also share insights from their own research on embodied practices in the Caribbean, Europe and India and answer questions such as: What can research on and through embodied practices tell us about systems of power and domination that move between the local and the global? How can performance practices which are informed by multiple locations and cultures be read and appreciated adequately? Sharing insights from his research into Guyanese prisons, Kerrigan outlines how he aims to connect everyday experiences and struggles of Caribbean people to trans-historical and transnational processes such as racial capitalism and post/coloniality. Furthermore, he elaborates on how he uses performance practices such as spoken word poetry and data verbalisation to connect with systematically excluded groups. Bala challenges naïve notions about the inherent transformative potential of performance in her research on performance and translation. She points to the way in which performance and its reception is always already inscribed in what she calls global or planetary asymmetries. At the conclusion of this conversation, they broach the question: are small places truly as small as they seem

Building Institutional Research Knowledge and Skills Through Communities of Practice Networks

The demands on and expectations of Institutional Research (IR) departments at colleges and universities have continued to expand over the years, yet there have been no studies on cost effective ways to develop and maintain the knowledge and skills needed by professionals in the field. Using a survey and social network analysis, this study explored the impact of participating in an Institutional Research (IR) affinity group on the development of the three tiers of organizational intelligence and the strength and nature of the social network that exists among the participants. The findings suggest that communities of practice, such as the IR affinity group, can aid the development and maintenance of some of the skills and knowledge related to the three tiers of organizational intelligence in the field of IR. The study also highlights how social network analysis can be used to explore communities of practice and approaches for professional development

An Ontology Model to Support the Automated Evaluation of Software

Even though previous research has tried to model Software Engineering knowledge, focusing either on the entire discipline or on parts of it, we lack an integrated conceptual model for representing software evaluations, and we also lack the information related to them that supports their definition and enables their automation and reproducibility. This paper presents an extensible ontology model for representing software evaluations and evaluation campaigns, i.e., worldwide activities where a group of tools is evaluated according to a certain evaluation specification using common test data. During the development of the ontologies, we have reused current standards and models and have linked these ontologies with some renowned ones

Understanding temperature effects on friction at tool – CFRP workpiece interface using open-loop friction testing

Cutting processes of carbon fibre reinforced polymer (CFRP) material generate significant energy in the form of heat which can be detrimental to final surface and sub-surface quality. By artificially changing the temperature of the workpiece to simulate cutting temperatures, thermal effects on friction metrics can be understood. Feed rate and CFRP pre-heating for macro and nanoscale open loop pin on plate friction testing has been completed for two aerospace grade CFRP materials with steel, carbide and coated carbide pins to give an insight to fundamental tool wear that occurs in CFRP machining

The rate of hypo-osmotic challenge influences regulatory volume decrease (RVD) and mechanical properties of articular chondrocytes

Zhao Wang is funded on a China Scholarships PhD Studentship. Jerome Irianto was supported on a project grant from The Wellcome Trust (ref no. 084717)

A comparative study of the effects of milling and abrasive water jet cutting on flexural performance of CFRP

Machining of carbon fibre reinforced polymers is part of the production process that introduces several challenges due to inherent characteristics of CFRPs such as non-homogeneity of their mechanical properties. A comparative analysis of conventional milling and abrasive water jet (AWJ) cutting is performed to quantify the effects of machining induced damage on flexural strength of woven CFRP laminates. The machined surfaces quality is characterized using optical and scanning electron microscopy methods prior to flexural mechanical testing. High-speed Digital Image Correlation technique is also used to measure deformation evolutions and determine fracture mechanisms in relation to the applied machining operation and produced machined surfaces. The effect of machining induced damage on strength of milled samples was less than expected with the AWJ processed samples having the least mechanical properties. The surface morphology analysis revealed that the entry and exit point of the water jet introduced severe surface and subsurface damage across the full thickness. The failure initiation sites were determined by strain distribution maps indicating that machining induced damage promotes failure of the tested CFRPs away from maximum compressive stress observed under the loading points

Activation of the innate immune receptor Dectin-1 upon formation of a 'phagocytic synapse'.

Innate immune cells must be able to distinguish between direct binding to microbes and detection of components shed from the surface of microbes located at a distance. Dectin-1 (also known as CLEC7A) is a pattern-recognition receptor expressed by myeloid phagocytes (macrophages, dendritic cells and neutrophils) that detects β-glucans in fungal cell walls and triggers direct cellular antimicrobial activity, including phagocytosis and production of reactive oxygen species (ROS). In contrast to inflammatory responses stimulated upon detection of soluble ligands by other pattern-recognition receptors, such as Toll-like receptors (TLRs), these responses are only useful when a cell comes into direct contact with a microbe and must not be spuriously activated by soluble stimuli. In this study we show that, despite its ability to bind both soluble and particulate β-glucan polymers, Dectin-1 signalling is only activated by particulate β-glucans, which cluster the receptor in synapse-like structures from which regulatory tyrosine phosphatases CD45 and CD148 (also known as PTPRC and PTPRJ, respectively) are excluded (Supplementary Fig. 1). The 'phagocytic synapse' now provides a model mechanism by which innate immune receptors can distinguish direct microbial contact from detection of microbes at a distance, thereby initiating direct cellular antimicrobial responses only when they are required

Varying CFRP workpiece temperature during slotting : effects on surface metrics, cutting forces and chip geometry

Carbon fibre reinforced thermoset polymer (CFRP) components are typically edge trimmed using a milling process to achieve final part shape. During this process the material is subject to significant heating at the tool-workpiece interface. Damage due to heating is fibre orientation specific; for some orientations it can lead to matrix smearing, potentially hiding defects and for others it can increase pullout. Understanding these relationships is critical to attaining higher throughput by edge milling. For the first time this study focuses on active heating of the CFRP rather than passive measurement, through use of a thermocouple controlled system to heat a CFRP workpiece material from room temperature (RT) up to 110 °C prior to machining. Differences in cutting mechanisms for fibres oriented at 0, 45, 90 and -45° are observed with scanning electron microscopy (SEM), and quantified with using focus variation with an increase of 89.9% Sa reported between RT and 110°C CFRP panel pre-heating. Relationships to cutting forces through dynamometer readings and tool temperature through infra-red (IR) measurements are also made with a novel optical method to measure cut chips presented. Results show an increase in chip length and width for increasing cutting temperature from RT to 110°C (3.39 and 0.79 µm for length and width, respectively). This work improves current understandings of how the cutting mechanism changes with increased temperature and suggests how improved milling throughput can be achieved