Time-frequency analysis of skeletal muscle and cardiac vibrations

Skeletal muscle and the heart vibrate during contraction producing nonstationary signals whose time-varying frequency reflects dynamic changes in physiological properties. Consequently, pathological changes in the mechanical integrity or loading of skeletal muscle or the heart can be expected to alter their vibrations. Classic frequency analysis techniques have been inadequate to characterize these subtle changes because of rapidly varying frequency components. A poor understanding of heart and muscle sound generation has also limited investigations. This paper demonstrates how time-frequency (TF) techniques have illuminated the relationships between muscle/heart material properties and loading and frequency dynamics of heart and muscle vibrations. Studies of evoked twitches from frog skeletal muscle reveal that muscle vibrations occur as transverse oscillations at the muscle's resonant frequency. Using a classic Rayleigh-Ritz model and crude estimates of the muscle geometry, muscle force can be accurately predicted from the muscle sound TF profile. First heart sound vibrations, in contrast, are shown to be a nonresonant phenomena, consisting of propagating transients superimposed upon bulk acceleration of myocardial contraction. Consequently, first heart sound frequency dynamics depend upon cardiac electrical excitation and hemodynamic loading in addition to intrinsic material properties and geometry, necessitating further work to characterize pathophysiologic correlations     

Situating L2 writing in global communication technologies

This article draws on the strengths of two fields—technology and intercultural studies—to present a model for theorizing and developing research methods that ethically and accurately situate L2 writing and communication technologies. Much research in communication technologies and writing use so-called localized approaches to intercultural inquiries. However, because these approaches focus on the concreteness of local situations, they do not provide a valid or ethical frame for understanding the influence of communication technologies across cultures. Because communication technologies restrain and reinforce certain communication possibilities and corresponding rhetorical and cultural patterns, they do not relate to or fit each cultural and rhetorical tradition the same way. Rather, communication technologies develop complexly different relations to each cultural and/or rhetorical tradition across the globe. Consequently, each rhetorical tradition uses each communication technology with a distinct sense of purpose, audience-author relations, information needs, and organizational patterns. This article first overviews the debate about technology-culture relationships and then explores how the difference-based lens cannot ethically and accurately situate L2 writing and technology. Next, drawing on research in intercultural studies and international human rights, the article sets up an intercultural frame for examining L2 writing and technologies. Finally, it puts into practice this intercultural-technology frame by looking at L2 writing in Ecuadorian contexts.     

The stability of long action chains in XCS

 XCS [1, 2] represents a new form of learning classifier system [3] that uses accuracy as a means of guiding fitness for selection within a Genetic Algorithm. The combination of accuracy-based selection and a dynamic niche-based deletion mechanism achieve a long sought-after goal–the reliable production, maintenance, and proliferation of the sub-population of optimally general accurate classifiers that map the problem domain [4]. Wilson [2] and Lanzi [5, 6] have demonstrated the applicability of XCS to the identification of the optimal action-chain leading to the optimum trade-off between reward distance and magnitude. However, Lanzi [6] also demonstrated that XCS has difficulty in finding an optimal solution to the long action-chain environment Woods-14 [7]. Whilst these findings have shed some light on the ability of XCS to form long action-chains, they have not provided a systematic and, above all, controlled investigation of the limits of XCS learning within multiple-step environments. In this investigation a set of confounding variables in such problems are identified. These are controlled using carefully constructed FSW environments [8, 9] of increasing length. Whilst investigations demonstrate that XCS is able to establish the optimal sub-population [O] [4] when generalisation is not used, it is shown that the introduction of generalisation introduces low bounds on the length of action-chains that can be identified and chosen between to find the optimal pathway. Where these bounds are reached a form of over-generalisation caused by the formation of dominant classifiers can occur. This form is further investigated and the Domination Hypothesis introduced to explain its formation and preservation.