Design of minimal-order stabilisers for multi-machine unstable power systems

A reduced dynamics stabiliser for multi-machine power systems is presented in this paper. The design of the stabiliser is based on the theory of linear functional observers and the solution of a simple parameter optimisation problem. The order of the stabiliser could be as low as the number of machines in the system. The design is applied to an open-loop unstable multi-machine power system.

Optimal lag-length choice in stable and unstable VAR models under situations of homoscedasticity and ARCH

The performance of different information criteria - namely Akaike, corrected Akaike (AICC), Schwarz-Bayesian (SBC), and Hannan-Quinn - is investigated so as to choose the optimal lag length in stable and unstable vector autoregressive (VAR) models both when autoregressive conditional heteroscedasticity (ARCH) is present and when it is not. The investigation covers both large and small sample sizes. The Monte Carlo simulation results show that SBC has relatively better performance in lag-choice accuracy in many situations. It is also generally the least sensitive to ARCH regardless of stability or instability of the VAR model, especially in large sample sizes. These appealing properties of SBC make it the optimal criterion for choosing lag length in many situations, especially in the case of financial data, which are usually characterized by occasional periods of high volatility. SBC also has the best forecasting abilities in the majority of situations in which we vary sample size, stability, variance structure (ARCH or not), and forecast horizon (one period or five). frequently, AICC also has good lag-choosing and forecasting properties. However, when ARCH is present, the five-period forecast performance of all criteria in all situations worsens.

Estimating the demand for money in an unstable open economy : the case of the Fiji Islands

In this paper, we estimate Fiji's money demand function for the period 1971-2002 based on the bounds testing approach to cointegration, which is applicable irrespective of whether or not the underlying variables are non-stationary. We estimate models with and without a time trend and for lag lengths ranging from 1-3, but fail to find any evidence for a long-run relationship. Moreover, our structural break analysis suggests that the unstable nature of Fiji's money demand may be due to atypical events, such as coups; the implementation of policies, such as devaluations and value added tax; and the onset of trade liberalisation policies over the last two decades.

No difference in 1RM strength and muscle activation during the barbell chest press on a stable and unstable surface

Exercise or Swiss balls are increasingly being used with conventional resistance exercises. There is little evidence supporting the efficacy of this approach compared to traditional resistance training on a stable surface. Previous studies have shown that force output may be reduced with no change in muscle electromyography (EMG) activity while others have shown increased muscle EMG activity when performing resistance exercises on an unstable surface. This study compared 1RM strength, and upper body and trunk muscle EMG activity during the barbell chest press exercise on a stable (flat bench) and unstable surface (exercise ball). After familiarization, 13 subjects underwent testing for 1RM strength for the barbell chest press on both a stable bench and an exercise ball, each separated by at least 7 days. Surface EMG was recorded for 5 upper body muscles and one trunk muscle from which average root mean square of the muscle activity was calculated for the whole 1RM lift and the concentric and eccentric phases. Elbow angle during each lift was recorded to examine any range-of-motion differences between the two surfaces. The results show that there was no difference in 1RM strength or muscle EMG activity for the stable and unstable surfaces. In addition, there was no difference in elbow range-of-motion between the two surfaces. Taken together, these results indicate that there is no reduction in 1RM strength or any differences in muscle EMG activity for the barbell chest press exercise on an unstable exercise ball when compared to a stable flat surface. Moreover, these results do not support the notion that resistance exercises performed on an exercise ball are more efficacious than traditional stable exercises.

The unstable print: Material challenges in printmaking and the moving image

The past few years have seen an emergence of printmakers motivated by moving-image technology to use print as performative creative practice; in film and animation, as installation and in various processes of thinking and production. Notions of movement and change that could be said to identify much of our contemporary world reflect the interests of a number of printmakers who utilize printmaking characteristics of multiplicity and reproduction by integrating the digital and the handmade within the moving-image. There seems to be a restlessness by some artists who wish to explore an unbounded, experimental approach to printmaking; perhaps it is a natural progression for printmakers to relate their processes of thinking and production to concepts of frame-by-frame production – to additive and subtractive methods, multiple imagery and the reproduced or copy. But what happens when printmaking that has entered the realm of multimedia technology returns to the physical, material print? This paper presents and discusses printmaking as moving image, and in particular the practice of printmaking that utilizes the copy and multiplicity while exploiting qualities of change through, for example, organic non-archival materials. Drawing from my own print projects and practice as well as the work of other Australian printmakers, the paper asks: can the physical print convincingly perform, not only represent, movement and change as analog experience through its materiality, and how is it to be valued within printmaking conventions concerned with longevity and permanence?