MOBILESAT: Australia's own

Australia will be introducing a dedicated Mobile Satellite Communications System following the launch of the AUSSAT-B satellites late in 1991. The Mobile Satellite System, MOBILESAT, will provide circuit switched voice/data services and packet-switched data services for land, aeronautical and maritime users. Here, an overview is given of the development program being undertaken within Australia to enable a fully commercial service to be introduced in 1992

Automated Markerless Extraction of Walking People Using Deformable Contour Models

We develop a new automated markerless motion capture system for the analysis of walking people. We employ global evidence gathering techniques guided by biomechanical analysis to robustly extract articulated motion. This forms a basis for new deformable contour models, using local image cues to capture shape and motion at a more detailed level. We extend the greedy snake formulation to include temporal constraints and occlusion modelling, increasing the capability of this technique when dealing with cluttered and self-occluding extraction targets. This approach is evaluated on a large database of indoor and outdoor video data, demonstrating fast and autonomous motion capture for walking people

Adaptive control of nonlinear dynamical systems using a model reference approach

In this paper we consider using a model reference adaptive control approach to control nonlinear systems. We consider the controller design and stability analysis associated with these type of adaptive systems. Then we discuss the use of model reference adaptive control algorithms to control systems which exhibit nonlinear dynamical behaviour using the example of a Duffing oscillator being controlled to follow a linear reference model. For this system we show that if the nonlinearity is “small” then standard linear model reference control can be applied. A second example, which is often found in synchronization applications, is when the nonlinearities in the plant and reference model are identical. Again we show that linear model reference adaptive control is sufficient to control the system. Finally we consider controlling more general nonlinear systems using adaptive feedback linearization to control scalar nonlinear systems. As an example we use the Lorenz and Chua systems with parameter values such that they both have chaotic dynamics. The Lorenz system is used as a reference model and a single coordinate from the Chua system is controlled to follow one of the Lorenz system coordinates

Periodic sticking motion in a two-degree of freedom impact oscillator

Periodic sticking motions can occur in vibro-impact systems for certain parameter ranges. When the coefficient of restitution is low (or zero), the range of periodic sticking motions can become large. In this work the dynamics of periodic sticking orbits with both zero and non-zero coefficient of restitution are considered. The dynamics of the periodic orbit is simulated as the forcing frequency of the system is varied. In particular, the loci of Poincaré fixed points in the sticking plane are computed as the forcing frequency of the system is varied. For zero coefficient of restitution, the size of the sticking region for a particular choice of parameters appears to be maximized. We consider this idea by computing the sticking region for zero and non-zero coefficient of restitution values. It has been shown that periodic sticking orbits can bifurcate via the rising/multi-sliding bifurcation. In the final part of this paper, we describe three types of post-bifurcation behavior which occur for the zero coefficient of restitution case. This includes two types of rising bifurcation and a border orbit crossing event

Constraints on the presence of water megamaser emission in z~2.5 ultraluminous infrared starburst galaxies

We present Expanded Very Large Array and Arecibo observations of two lensed submm galaxies at z~2.5, in order to search for redshifted 22.235 GHz water megamaser emission. Both SMM J14011+0252 and SMM J16359+6612 have multi-wavelength characteristics consistent with ongoing starburst activity, as well as CO line emission indicating the presence of warm molecular gas. Our observations do not reveal any evidence for H2O megamaser emission in either target, while the lensing allows us to obtain deep limits to the H_2O line luminosities, L(H2O) < 7470 Lsun (3-sigma) in the case of SMM J14011+0252, and L(H2O) < 1893 Lsun for SMM J16359+6612, assuming linewidths of 80 km/s. Our search for, and subsequent non-detection of H2O megamaser emission in two strongly lensed starburst galaxies, rich in gas and dust, suggests that such megamaser emission is not likely to be common within the unlensed population of high-redshift starburst galaxies. We use the recent detection of strong H2O megamaser emission in the lensed quasar, MG J0414+0534 at z = 2.64 to make predictions for future EVLA C-band surveys of H2O megamaser emission in submm galaxies hosting AGN.Comment: AJ accepte

AUSSAT mobile satellite services

An overview of AUSSAT's planned mobile satellite system is given. The development program which is being undertaken to achieve the 1992 service date is described. Both business and technical aspects of the development program are addressed

Understanding the dynamics of multi-degree-of-freedom nonlinear systems using backbone curves

In this paper we will describe how backbone curves can be used to explain complex dynamic phenomena that can occur in coupled multi-degree-of-freedom physical systems. Three examples will be used to demonstrate some key points. We will describe cases when backbone curves can be decoupled. In the case of nonlinear resonance (or modal interaction) we explain how to distinguish how many modes are interacting, their unison and relative phase characteristics. Bifurcation of higher order interaction curves from the lower order curves will also be discussed. Finally we will consider an example based on the transverse vibration of a thin plate with pinned boundary conditions. Both finite element simulations and a low order differential equation model are developed for this system. The results show the importance of the nonlinear coupling terms in replicating the frequency shift phenomena which is known to occur in structures of this type. Despite its much smaller size, the low order model is able to show qualitative agreement with the finite element model. Knowledge of the backbone curve behaviour for this system, is used to explain the forced damped behaviour

Supporting brace sizing in structures with added linear viscous fluid dampers: A filter design solution

Viscous fluid dampers have proved to be effective in suppressing unwanted vibrations in a range of engineering structures. When dampers are fitted in a structure, a brace is typically used to attach them to the main structure. The stiffness of this brace can significantly alter the effectiveness of the damper, and in structures with multiple dampers, this can be a complex scenario to model. In this paper, we demonstrate that the effects of the brace compliance on the damper performance can be modelled by way of a first-order filter. We use this result to formulate a procedure that calculates the stiffness required by the supporting brace to provide a specified effectiveness of the damping action. The proposed procedure assumes that viscous dampers have been sized in a previous design step based on any optimal methodology in which, as is usually the case, the presence of supporting braces and their dynamic effects were neglected. Firstly considering a one degree-of-freedom system, we show that the proposed method ensures a desired level of damper efficiency for all frequencies within a selected bandwidth. Then the analysis is extended to the case of multi-degree-of-freedom systems to show that the design criteria can be applied in a straightforward and successful manner to more complex structures