A refinement indicator for adaptive quasicontinuum approaches for structural lattices

in International Journal for Numerical Methods in Engineering (in press)

The quasicontinuum method is a concurrent multiscale approach in which lattice models are fully resolved in small regions of interest and coarse-grained elsewhere. Since the method was originally proposed ... [more ▼]

The quasicontinuum method is a concurrent multiscale approach in which lattice models are fully resolved in small regions of interest and coarse-grained elsewhere. Since the method was originally proposed to accelerate atomistic lattice simulations, its refinement criteria – that drive refining coarse-grained regions and/or increasing fully-resolved regions – are generally associated with quantities relevant to the atomistic scale. In this contribution, a new refinement indicator is presented, based on the energies of dedicated cells at coarse-grained domain surfaces. This indicator is incorporated in an adaptive scheme of a generalization of the quasicontinuum method able to consider periodic representative volume elements, like the ones employed in most computational homogenization approaches. However, this indicator can also be used for conventional quasicontinuum frameworks. Illustrative numerical examples of elastic indentation and scratch of different lattices demonstrate the capabilities of the refinement indicator and its impact on adaptive quasicontinuum simulations. [less ▲]

Reflective Practice: Lessons Learnt by Using Board Games as a Design Tool for Location-Based Games

in Kyriakidis, P; Hadjimitsis, D; Skarlatos, D (Eds.) et al Geospatial Technologies for Local and Regional Development (2019)

Location-based gaming (LBG) apps present many challenges to the design process. They have very different requirements compared to games that are aspatial in nature. They take place in the wild and this ... [more ▼]

Location-based gaming (LBG) apps present many challenges to the design process. They have very different requirements compared to games that are aspatial in nature. They take place in the wild and this brings unique challenges to the practicalities of their design. There is a need to balance the core game play with the spatial requirements of location-aware technologies as well as considering the overall theme and objectives of the game together with the motivations and behaviours of players. We reflect upon this balancing act and explore an approach to creative paper prototyping through the medium of board games to co-design LBG requirements. We examine two case studies of location-based games with different goals. The first case study discusses the CrossCult Pilot 4 app built to trigger reflection on historical stories through thoughtful play. Whilst the second case study uses the City Conquerer app designed and played in Suzhou, China with a view to exploring notions of territoriality. The paper considers how spatial, social and interaction metaphors are used to simulate location-based games in a board game and discusses the lessons learned when transforming the paper game into a digital prototype. It forms part of a thinking by doing approach. By comparing the board games to the technical counterparts, we consider how effective are the features and activities implemented in the technology prototypes. We propose a set of 11 design constraints that developers must be mindful of when transitioning from paper to digital prototypes. [less ▲]

Regions of stability for limit cycle oscillations in piecewise linear systems

in IEEE Transactions on Automatic Control (2005), 50(11), 1877-1882

Oscillations appear in numerous applications from biology to technology.However, besides local results, rigorous stability and robustness analysis of oscillations are rarely done due to their intrinsic ... [more ▼]

Oscillations appear in numerous applications from biology to technology.However, besides local results, rigorous stability and robustness analysis of oscillations are rarely done due to their intrinsic nonlinear behavior. Poincarémaps associated with the system cannot typically be found explicitly and stability is estimated using extensive simulations and experiments. This paper gives conditions in the form of linear matrix inequalities (LMIs) that guarantee asymptotic stability in a reasonably large region around a limit cycle for a class of systems known as piecewise linear systems (PLS). Such conditions, based on recent results on impact maps and surface Lyapunov functions (SuLF), allow a systematic and efficient analysis of oscillations of PLS or arbitrarily close approximations of nonlinear systems by PLS. The methodology applies to any locally stable limit cycle of a PLS, regardless of the dimension and the number of switching surfaces of the system, and is illustrated with a biological application: a fourth-order neural oscillator, also used in many robotics applications such as juggling and locomotion. [less ▲]

Reliability of network-wide traffic management

Scientific Conference (2021, June)

Removing the saturation assumption in Bank-Weiser error estimator analysis in dimension three

in Applied Mathematics Letters (2020), 107

We provide a new argument proving the reliability of the Bank-Weiser estimator for Lagrange piecewise linear finite elements in both dimension two and three. The extension to dimension three constitutes ... [more ▼]

We provide a new argument proving the reliability of the Bank-Weiser estimator for Lagrange piecewise linear finite elements in both dimension two and three. The extension to dimension three constitutes the main novelty of our study. In addition, we present a numerical comparison of the Bank-Weiser and residual estimators for a three-dimensional test case. [less ▲]

Representing Structure in Linear Interconnected Dynamical Systems

in The proceedings of the 49th IEEE Conference on Decision and Control (CDC) (2010)

Interconnected dynamical systems are a pervasive component in our modern world's infrastructure. One of the fundamental steps to understanding the complex behavior and dynamics of these systems is ... [more ▼]

Interconnected dynamical systems are a pervasive component in our modern world's infrastructure. One of the fundamental steps to understanding the complex behavior and dynamics of these systems is determining how to appropriately represent their structure. In this work, we discuss different ways of representing a system's structure. We define and present, in particular, four representations of system structure-complete computational, subsystem, signal, and zero pattern structure-and discuss some of their fundamental properties. We illustrate their application with a numerical example and show how radically different representations of structure can be consistent with a single LTI input-output system. [less ▲]

A review of nature-based solutions for resource recovery in cities

in Blue-Green System (2020), 2(1)

Our modern cities are resource sinks designed on the current linear economic model which recovers very little of the original input. As the current model is not sustainable, a viable solution is to ... [more ▼]

Our modern cities are resource sinks designed on the current linear economic model which recovers very little of the original input. As the current model is not sustainable, a viable solution is to recover and reuse parts of the input. In this context, resource recovery using nature-based solutions (NBS) is gaining popularity worldwide. In this specific review, we focus on NBS as technologies that bring nature into cities and those that are derived from nature, using (micro)organisms as principal agents, provided they enable resource recovery. The findings presented in this work are based on an extensive literature review, as well as on original results of recent innovation projects across Europe. The case studies were collected by participants of the COST Action Circular City, which includes a portfolio of more than 92 projects. The present review article focuses on urban wastewater, industrial wastewater, municipal solid waste and gaseous effluents, the recoverable products (e.g., nutrients, nanoparticles, energy), as well as the implications of source-separation and circularity by design. The analysis also includes assessment of the maturity of different technologies (technology readiness level) and the barriers that need to be overcome to accelerate the transition to resilient, self-sustainable cities of the future. [less ▲]

Rhythmic regulation of Ca2+ signalling networks

Scientific Conference (2006)

The circadian clock is the internal timekeeper of plants. This clock regulates most aspects of plant physiology providing considerable competitive advantage. We are investigating the role for oscillations ... [more ▼]

The circadian clock is the internal timekeeper of plants. This clock regulates most aspects of plant physiology providing considerable competitive advantage. We are investigating the role for oscillations in the cytosolic free Ca2+ concentration ([Ca2+]cyt) in the circadian control of cellular physiology. We have previously demonstrated that circadian oscillations of [Ca2+]cyt encode photoperiodic information but the precise role of circadian [Ca2+]cyt oscillations remain obscure. We have been taking a systems wide approach to determine the origin and function of circadian oscillations of [Ca2+]cyt. Using pharmacology, bioinformatics and biochemical tools we have new evidence that oscillations of [Ca2+]cyt are generated by the small signalling intermediate, cADPR. Positioning the oscillations of [Ca2+]cyt with respect to the molecular oscillator using reverse genetics indicates that [Ca2+]cyt is an output of the clock. Using a whole genome transcriptional profile we have identified over 1800 circadian-regulated transcripts, many of which encode for Ca2+ signalling elements. The function of circadian-regulated transcripts encoding signalling components is being investigated by reverse genetic screens with automated imaging. Using our extensive data sets describing the circadian regulation of [Ca2+]cyt in different backgrounds and conditions we have constructed a mathematical model. This is being validated using mutant analysis and refined by introducing complexity to the model. Our data and models suggest that [Ca2+]cyt acts an output of the clock that regulates diverse aspects of physiology and has the potential to form a feedback loop with the molecular components of the oscillator. [less ▲]

Risk-averse Stochastic Nonlinear Model Predictive Control for Real-time Safety-critical Systems

in The 20th World Congress of the International Federation of Automatic Control, IFAC 2017 World Congress, Toulouse, France, 9-14 July 2017 (2017, July 11)

Stochastic nonlinear model predictive control has been developed to systematically find an optimal decision with the aim of performance improvement in dynamical systems that involve uncertainties. However ... [more ▼]

Stochastic nonlinear model predictive control has been developed to systematically find an optimal decision with the aim of performance improvement in dynamical systems that involve uncertainties. However, most of the current methods are risk-neutral for safety-critical systems and depend on computationally expensive algorithms. This paper investigates on the risk-averse optimal stochastic nonlinear control subject to real-time safety-critical systems. In order to achieve a computationally tractable design and integrate knowledge about the uncertainties, bounded trajectories generated to quantify the uncertainties. The proposed controller considers these scenarios in a risk-sensitive manner. A certainty equivalent nonlinear model predictive control based on minimum principle is reformulated to optimise nominal cost and expected value of future recourse actions. The capability of proposed method in terms of states regulations, constraints fulfilment, and real-time implementation is demonstrated for a semi-autonomous ecological advanced driver assistance system specified for battery electric vehicles. This system plans for a safe and energy-efficient cruising velocity profile autonomously. [less ▲]

RIVER MORPHOLOGY MONITORING OF A SMALL-SCALE ALPINE RIVERBED USING DRONE PHOTOGRAMMETRY AND LIDAR

in The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences (2020, August 12), XLIII-B2-2020 Article Metrics Related articles(1017), 1024

An efficient alternative to labour-intensive terrestrial and costly airborne surveys is the use of small, inexpensive Unmanned Aerial Vehicles (UAVs) or Remotely Piloted Aerial Systems (RPAS). These low ... [more ▼]

An efficient alternative to labour-intensive terrestrial and costly airborne surveys is the use of small, inexpensive Unmanned Aerial Vehicles (UAVs) or Remotely Piloted Aerial Systems (RPAS). These low-altitude remote sensing platforms, commonly known as drones, can carry lightweight optical and LiDAR sensors. Even though UAV systems still have limited endurance, they can provide a flexible and relatively inexpensive monitoring solution for a limited area of interest. This study investigated the applicability of monitoring the morphology of a frequently changing glacial stream using high-resolution topographic surface models derived from low-altitude UAV-based photogrammetry and LiDAR. An understanding of river-channel morphology and its response to anthropogenic and natural disturbances is imperative for effective watershed management and conservation. We focus on the data acquisition, processing workflow and highlight identified challenges and shortcomings. Additionally, we demonstrate how LiDAR data acquisition simulations can help decide which laser scanning approach to use and help optimise data collection to ensure full coverage with desired level of detail. Lastly, we showcase a case study of 3D surface change analysis in an alpine stream environment with UAV-based photogrammetry. The datasets used in this study were collected as part of the ISPRS Summer School of Alpine Research, which will continue to add new data layers on a biyearly basis. This growing data repository is freely available for research. [less ▲]