Modal parameter estimation in the presence of non-linearities

This paper investigates the use of time-frequency techniques to assist in the estimation of power system modes which are resolvable by a Digital Fourier Transform (DFT). The limitations of linear estimation techniques in the presence of large disturbances which excite system non-linearities, particularly the swing equation non-linearity are shown. Where a nonlinearity manifests itself as time varying modal frequencies the Wigner-Ville Distribution (WVD) is used to describe the variation in modal frequencies and construct a window over which standard linear estimation techniques can be used. The error obtained even in the presence of multiple resolvable modes is better than 2%.

Beyond the controller

Performance / presentation given at Freeplay 2010, Melbourne, Victoria as an invited guest for a session entitled "Beyond the controller" This performance intended to review the follies of tangible interface design for games since the appearance of games specific control peripherals in the 1980s. In this work I examine: Technology as prosthesis – designed artefacts that enable interaction in a virtual world; Technology as the dream of virtuality – mind-ware. IN each instance the controller DICTATES the form of interaction

Multi-objective optimisation of bijective s-boxes

In this paper we investigate the heuristic construction of bijective s-boxes that satisfy a wide range of cryptographic criteria including algebraic complexity, high nonlinearity, low autocorrelation and have none of the known weaknesses including linear structures, fixed points or linear redundancy. We demonstrate that the power mappings can be evolved (by iterated mutation operators alone) to generate bijective s-boxes with the best known tradeoffs among the considered criteria. The s-boxes found are suitable for use directly in modern encryption algorithms.

Pattern recognition using invariants defined from higher order spectra : 2-D image inputs

A new algorithm for extracting features from images for object recognition is described. The algorithm uses higher order spectra to provide desirable invariance properties, to provide noise immunity, and to incorporate nonlinearity into the feature extraction procedure thereby allowing the use of simple classifiers. An image can be reduced to a set of 1D functions via the Radon transform, or alternatively, the Fourier transform of each 1D projection can be obtained from a radial slice of the 2D Fourier transform of the image according to the Fourier slice theorem. A triple product of Fourier coefficients, referred to as the deterministic bispectrum, is computed for each 1D function and is integrated along radial lines in bifrequency space. Phases of the integrated bispectra are shown to be translation- and scale-invariant. Rotation invariance is achieved by a regrouping of these invariants at a constant radius followed by a second stage of invariant extraction. Rotation invariance is thus converted to translation invariance in the second step. Results using synthetic and actual images show that isolated, compact clusters are formed in feature space. These clusters are linearly separable, indicating that the nonlinearity required in the mapping from the input space to the classification space is incorporated well into the feature extraction stage. The use of higher order spectra results in good noise immunity, as verified with synthetic and real images. Classification of images using the higher order spectra-based algorithm compares favorably to classification using the method of moment invariants

Higher order spectral analysis of Chua's circuit

Higher order spectral analysis is used to investigate nonlinearities in time series of voltages measured from a realization of Chua's circuit. For period-doubled limit cycles, quadratic and cubic nonlinear interactions result in phase coupling and energy exchange between increasing numbers of triads and quartets of Fourier components as the nonlinearity of the system is increased. For circuit parameters that result in a chaotic Rossler-type attractor, bicoherence and tricoherence spectra indicate that both quadratic and cubic nonlinear interactions are important to the dynamics. When the circuit exhibits a double-scroll chaotic attractor the bispectrum is zero, but the tricoherences are high, consistent with the importance of higher-than-second order nonlinear interactions during chaos associated with the double scroll.

Higher-order spectral analysis of nonlinear ocean surface gravity waves

Higher-order spectral analysis is used to detect the presence of secondary and tertiary forced waves associated with the nonlinearity of energetic swell observed in 8- and 13-m water depths. Higher-order spectral analysis techniques are first described and then applied to the field data, followed by a summary of the results.

Bispectral and trispectral characterization of transition to chaos in the Duffing oscillator

Higher-order spectral (bispectral and trispectral) analyses of numerical solutions of the Duffing equation with a cubic stiffness are used to isolate the coupling between the triads and quartets, respectively, of nonlinearly interacting Fourier components of the system. The Duffing oscillator follows a period-doubling intermittency catastrophic route to chaos. For period-doubled limit cycles, higher-order spectra indicate that both quadratic and cubic nonlinear interactions are important to the dynamics. However, when the Duffing oscillator becomes chaotic, global behavior of the cubic nonlinearity becomes dominant and quadratic nonlinear interactions are weak, while cubic interactions remain strong. As the nonlinearity of the system is increased, the number of excited Fourier components increases, eventually leading to broad-band power spectra for chaos. The corresponding higher-order spectra indicate that although some individual nonlinear interactions weaken as nonlinearity increases, the number of nonlinearly interacting Fourier modes increases. Trispectra indicate that the cubic interactions gradually evolve from encompassing a few quartets of Fourier components for period-1 motion to encompassing many quartets for chaos. For chaos, all the components within the energetic part of the power spectrum are cubically (but not quadratically) coupled to each other.

Everything is political

Everything is Political Ben Eltham, Kieran Lord, Jeff Brand, Truna. Chair: Daniel Golding Videogames don’t exist in isolation. They are part of artistic, cultural, and political spheres – even if some would much rather they weren’t. This panel takes a look at the way videogames are used as political tools and how we as developers and critics can better engage with that, and perhaps wrestle some of the conversation back into our hands.

That one piece of advice - microlecture

Programme: In these microlectures, developers, educators, critics, and artists give you the one piece of advice that they hold above all others. That one piece of advice: It's about the passion: Excerpt: Shades of madness - Creativity - Passion: There is something very important to observe about an industry that engages in these intense weekends. The monolithic Hollywood model is not viable, we need to scaffold the next gen of game designers, foster the passion, provide opportunity, CHANGE the model – not just dress it in new clothes

Journeys with friends

Journeys with Friends Truna aka J. Turner, Giselle Rosman and Matt Ditton Panel Session description: We are no longer an industry (alone) we are a sector. Where the model once consisted of industry making games, we now see the rise of a cultural sector playing in the game space – industry, indies (for whatever that distinction implies) artists (another odd distinction), individuals and well … everyone and their mums. This evolution has an affect – on audiences and who they are, what they expect and want, and how they understand the purpose and language of these “digital game forms’; how we talk about our worlds and the kinds of issues that are raised; on what we create and how we create it and on our communities and who we are. This evolution has an affect on how these works are understood within the wider social context and how we present this understanding to the next generation of makers and players. We can see the potential of this evolution from industry to sector in the rise of the Australian indie. We can see the potential fractures created by this evolution in the new voices that ask questions about diversity and social justice. And yet, we still see a ‘solution’ type reaction to the current changing state of our sector which announces the monolithic, Fordist model as desirable (albeit in smaller form) – with the subsequent ramifications for ‘training’ and production of local talent. Experts talk about a mismatch of graduate skills and industry needs, insufficient linkages between industry and education providers and the need to explore opportunity for the now passing model in new spaces such as adver-games and serious games. Head counts of Australian industry don’t recognise trans media producers as being part of their purview or opportunity, they don’t count the rise of the cultural playful game inspired creative works as one of thier team. Such perspectives are indeed relevant to the Australian Games Industry, but what about the emerging Australian Games Sector? How do we enable a future in such a space? This emerging sector is perhaps best represented by Melbourne’s Freeplay audience: a heady mix of indie developers, players, artists, critical thinkers and industry. Such audiences are no longer content with an ‘industry’ alone; they are the community who already see themselves as an important, vibrant cultural sector. Part of the discussion presented here seeks to identify and understand the resources, primarily in the context of community and educational opportunities, available to the evolving sector now relying more on the creative processes. This creative process and community building is already visibly growing within the context of smaller development studios, often involving more multiskilling production methodologies where the definition of ‘game’ clearly evolves beyond the traditional one.

Effective shear modulus approach for two dimensional solids and plate bending problems by meshless point collocation method

For the analysis of material nonlinearity, an effective shear modulus approach based on the strain control method is proposed in this paper by using point collocation method. Hencky’s total deformation theory is used to evaluate the effective shear modulus, Young’s modulus and Poisson’s ratio, which are treated as spatial field variables. These effective properties are obtained by the strain controlled projection method in an iterative manner. To evaluate the second order derivatives of shape function at the field point, the radial basis function (RBF) in the local support domain is used. Several numerical examples are presented to demonstrate the efficiency and accuracy of the proposed method and comparisons have been made with analytical solutions and the finite element method (ABAQUS).

Pinned fronts in heterogeneous media of jump type

In this paper, we analyse the impact of a (small) heterogeneity of jump type on the most simple localized solutions of a 3-component FitzHugh–Nagumo-type system. We show that the heterogeneity can pin a 1-front solution, which travels with constant (non-zero) speed in the homogeneous setting, to a fixed, explicitly determined, distance from the heterogeneity. Moreover, we establish the stability of this heterogeneous pinned 1-front solution. In addition, we analyse the pinning of 1-pulse, or 2-front, solutions. The paper is concluded with simulations in which we consider the dynamics and interactions of N-front patterns in domains with M heterogeneities of jump type (N = 3, 4, M ≥ 1).