Agricultural Trade Reform and Industry Adjustment in Indonesia

This paper presents a component of a project on industry adjustment to agricultural trade reform in selected developing countries. The aim of the project is to examine the issues affecting the development of industry adjustment policies to manage the impact of trade reform. It will evaluate specific developing country examples of industries that are likely to face significant adjustment pressures from trade policy reform. The study is focused on industry specific policy responses for two reasons. First, many LDC's are concerned about the consequences of future WTO reforms for adjustment in 'sensitive' industries. Governments in developing countries have received advice and assistance on how to comply with the requirements of their WTO commitments from the Uruguay Round of trade negotiations. However, very little attention has been devoted to the domestic effects of trade reform. Second, the implementation of international trade commitments is likely to lead to industry requests for assistance. Adjustment policies used by developed countries may not be directly applicable to LDC situations. Differences in structural characteristics, institutional arrangements and the level of industry development require an investigation of the issues affecting adjustment in developing countries.International Relations/Trade,

Agricultural Policy Reform and Industry Adjustment in Australia and New Zealand

Some sectors of Australian and New Zealand farming have been heavily assisted in the past. New Zealand underwent an economy-wide deregulation in the mid-to-late 980s that included abrupt removal of practically all agricultural assistance. Policy reform in Australia has been more gradual and is industry focused, but in some cases substantial industry assistance has been withdrawn. Deregulation of the Australian dairy industry, and that of the sheep and beef sector in New Zealand, are discussed as case studies of these deregulations. Conclusions are drawn from these experiences, a major one being that previously-assisted farmers can successfully make the transition to market-driven agriculture.agricultural adjustment, policy reform, Australia, New Zealand, Agricultural and Food Policy,

Computational Dynamics of a 3D Elastic String Pendulum Attached to a Rigid Body and an Inertially Fixed Reel Mechanism

A high fidelity model is developed for an elastic string pendulum, one end of which is attached to a rigid body while the other end is attached to an inertially fixed reel mechanism which allows the unstretched length of the string to be dynamically varied. The string is assumed to have distributed mass and elasticity that permits axial deformations. The rigid body is attached to the string at an arbitrary point, and the resulting string pendulum system exhibits nontrivial coupling between the elastic wave propagation in the string and the rigid body dynamics. Variational methods are used to develop coupled ordinary and partial differential equations of motion. Computational methods, referred to as Lie group variational integrators, are then developed, based on a finite element approximation and the use of variational methods in a discrete-time setting to obtain discrete-time equations of motion. This approach preserves the geometry of the configurations, and leads to accurate and efficient algorithms that have guaranteed accuracy properties that make them suitable for many dynamic simulations, especially over long simulation times. Numerical results are presented for typical examples involving a constant length string, string deployment, and string retrieval. These demonstrate the complicated dynamics that arise in a string pendulum from the interaction of the rigid body motion, elastic wave dynamics in the string, and the disturbances introduced by the reeling mechanism. Such interactions are dynamically important in many engineering problems, but tend be obscured in lower fidelity models.Comment: 17 pages, 14 figure

Optimal Control of a Rigid Body using Geometrically Exact Computations on SE(3)

Optimal control problems are formulated and efficient computational procedures are proposed for combined orbital and rotational maneuvers of a rigid body in three dimensions. The rigid body is assumed to act under the influence of forces and moments that arise from a potential and from control forces and moments. The key features of this paper are its use of computational procedures that are guaranteed to preserve the geometry of the optimal solutions. The theoretical basis for the computational procedures is summarized, and examples of optimal spacecraft maneuvers are presented.Comment: IEEE Conference on Decision and Control, 2006. 6 pages, 19 figure

Time Optimal Attitude Control for a Rigid Body

A time optimal attitude control problem is studied for the dynamics of a rigid body. The objective is to minimize the time to rotate the rigid body to a desired attitude and angular velocity while subject to constraints on the control input. Necessary conditions for optimality are developed directly on the special orthogonal group using rotation matrices. They completely avoid singularities associated with local parameterizations such as Euler angles, and they are expressed as compact vector equations. In addition, a discrete control method based on a geometric numerical integrator, referred to as a Lie group variational integrator, is proposed to compute the optimal control input. The computational approach is geometrically exact and numerically efficient. The proposed method is demonstrated by a large-angle maneuver for an elliptic cylinder rigid body.Comment: v1: 6 pages, 3 figures v2: 7 pages, 2 figures, more carefully addressed the issue of singular arc

Lagrangian Mechanics and Variational Integrators on Two-Spheres

Euler-Lagrange equations and variational integrators are developed for Lagrangian mechanical systems evolving on a product of two-spheres. The geometric structure of a product of two-spheres is carefully considered in order to obtain global equations of motion. Both continuous equations of motion and variational integrators completely avoid the singularities and complexities introduced by local parameterizations or explicit constraints. We derive global expressions for the Euler-Lagrange equations on two-spheres which are more compact than existing equations written in terms of angles. Since the variational integrators are derived from Hamilton's principle, they preserve the geometric features of the dynamics such as symplecticity, momentum maps, or total energy, as well as the structure of the configuration manifold. Computational properties of the variational integrators are illustrated for several mechanical systems.Comment: 19 pages, 7 figure

Efficient reorientation of a deformable body in space: A free-free beam example

It is demonstrated that the planar reorientation of a free-free beam in zero gravity space can be accomplished by periodically changing the shape of the beam using internal actuators. A control scheme is proposed in which electromechanical actuators excite the flexible motion of the beam so that it rotates in the desired manner with respect to a fixed inertial reference. The results can be viewed as an extension of previous work to a distributed parameter case