Stable imposition of stiff constraints in explicit dynamics for embedded finite element methods

We investigate various strategies to enforce the kinematics at an embedded interface for transient problems within the extended finite element method. In particular, we focus on explicit time integration of the semi‐discrete equations of motion and extend both dual and primal variational frameworks for constraint enforcement to a transient regime. We reiterate the incompatibility of the dual formulation with purely explicit time integration and the severe restrictions placed by the Courant–Friedrichs–Levy condition on primal formulations. We propose an alternate, consistent formulation for the primal method and derive an estimate for the stabilization parameter, which is more amenable in an explicit dynamics framework. Importantly, the use of the new estimate circumvents the need for any tolerances as an interface approaches an element boundary. We also show that with interfacial constraints, existing mass lumping schemes can lead to prohibitively small critical time steps. Accordingly, we propose a mass lumping procedure, which provides a more favorable estimate. These techniques are then demonstrated on several benchmark numerical examples, where we compare and contrast the accuracy of the primal methods against the dual methods in enforcing the constraints. Copyright © 2012 John Wiley & Sons, Ltd.     

Improved asymptotic stability conditions for neural networks with discrete and distributed delays

This paper considers the asymptotic stability problem for a class of neural networks with discrete and distributed delays. Based on a new augmented Lyapunov functional and integral inequalities, the new asymptotic stability condition is established in terms of linear matrix inequality. Meanwhile, the importance of some augmented terms in the Lyapunov functional are discussed. Compared with previous methods to deal with the distributed delay, our method is less conservative due to the use of the new Lyapunov functional. Finally, numerical examples illustrate the relaxation of obtained results and our claims.     

LMI searches for anticausal and noncausal rational Zames–Falb multipliers

Given a linear time-invariant plant, the search for a suitable multiplier over the class of Zames–Falb multipliers is a challenging problem which has been studied for several decades. Recently, a new linear matrix inequality search has been proposed over rational and causal Zames–Falb multipliers. This letter analyzes the conservatism of the restriction to causality on the multipliers and presents a complementary search for rational and anticausal multipliers. The addition of a Popov multiplier to the anticausal Zames–Falb multiplier is implemented by analogy with the causal search. As a result, a search over a noncausal subset of Zames–Falb multipliers is obtained. A comparison between all the search methods proposed in the literature is given.     

A novel augmented Lagrangian‐based formulation for upper‐bound limit analysis

This paper describes a novel upper‐bound formulation of limit analysis. This formulation is an innovative variant of an existing two‐field mixed formulation based on the augmented Lagrangian method also developed by the authors. A natural approach is used to describe the deformation of each finite element. Furthermore, and in contrast to the previous formulation, two independent field approximations are now both used to define the velocity field, defined globally and at element level. It is shown that this feature allows a governing system of uncoupled linear equations to be obtained. Some numerical examples in plane strain conditions are presented in order to illustrate the current model performance. In conclusion, the potential and advantages of this new approach are discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Augmented reality in language learning: A state-of-the-art review of 2014–2019

This systematic review study synthesizes research findings pertaining to the use of augmented reality (AR) in language learning. Published research from 2014 to 2019 has been explored and specific inclusion and exclusion criteria have been applied resulting in 54 relevant publications. Our findings determined: (a) devices and software employed for mastering AR; languages and contexts in which AR had been applied; theoretical perspectives adopted for guiding the use of AR; the number of participants in AR activities and benefits from using AR as an educational tool in the language classroom; (b) alignment of the affordances of Augmented Reality with the KSAVE (Knowledge, Skills, Attitudes, Values, Ethics) 21st-century skills framework; (c) future directions in AR research and practice. The main findings from this review demonstrate the popularity of mobile-based AR for supporting vocabulary (23.9%), reading (12.7%), speaking (9.9%) writing (8.5%) or generic language skills (9.9%). Our findings also uncovered areas that merit future attention in the application of AR in language learning – for instance learning theories were not often considered in the implementation of AR. The study concludes with suggestions for future research especially in the areas of instructional design and user experience.     

Compact see‐through near‐eye display with depth adaption

Based on the recent development of Pancharatnam–Berry deflectors and lenses, we propose a compact and lightweight near‐eye display system with depth adaption. The compact design results from the polarization selectivity of Pancharatnam–Berry deflector waveguide coupler, and the fast‐switching Pancharatnam–Berry lenses can be exploited for generating correct light fields.     

Open Augmented Reality Standards： Current Activities in Standards- Development Organizations

Augmented reality (AR) has emerged from research laboratories and is now being accepted in other domains as an attractive way of visualizing information.Before AR can be used in the mass market,there are a number of obstacles that need to be overcome.Several of these can be overcome by adopting open standards.A global grassroots community seeking open,interoperable AR content and experiences began to take shape in early 2010.This community is working collaboratively to reduce the barriers to the flow of data from content provider to AR end user.Standards development organizations and industry groups that provide open interfaces for AR meet regularly to provide updates,identify complementary work,and seek harmonization.The community also identifies deployer and implementer needs,communicates requirements,and discusses emerging challenges that could be resolved with standards.In this article,we describe current activities in international standards-development organizations.We summarize the AR standards gap analysis and shed light on special considerations for using standards in mobile AR.     

Efficient solution of the diesel-engine optimal control problem by time-domain decomposition

Offline solutions of the optimal control problems relating to diesel engines provide implications for causal control strategies and serve as a tool to automate the engine calibration process. However, the numerical solution of these dynamic optimisation problems is challenging. Above all, the model evaluations are expensive, integral and local inequality constraints are present, and the time horizon to be considered is long. Generally, the continuous problem is transcribed into a nonlinear mathematical program, which has a runtime that increases superlinearly with the problem size. In the literature, the time-domain decomposition of unconstrained and control-constrained problems is proposed to alleviate this often prohibiting increase in computational time. This paper extends the decomposition approach to problems with integral inequality constraints by utilising a partially dual formulation to derive equivalence conditions. To achieve these conditions, exact and approximate iteration schemes are proposed. The time-domain decomposition is combined with an iterative mesh refinement and a parallelisation of the model evaluations, which dominate the runtime of the solution process. On a standard personal computer, an overall speedup factor of 25 is achieved for a realistically sized instance of the diesel-engine problem.     

On multipliers for bounded and monotone nonlinearities

Recent results in equivalence between classes of multipliers for slope-restricted nonlinearities are extended to multipliers for bounded and monotone nonlinearities. This extension requires a slightly modified version of the Zames–Falb theorem and a more general definition of phase-substitution. The results in this paper resolve apparent contradictions in the literature on classes of multipliers for bounded and monotone nonlinearities.