Order Parameter Equations for Front Transitions: Nonuniformly Curved Fronts

Kinematic equations for the motion of slowly propagating, weakly curved fronts in bistable media are derived. The equations generalize earlier derivations where algebraic relations between the normal front velocity and its curvature are assumed. Such relations do not capture the dynamics near nonequilibrium Ising-Bloch (NIB) bifurcations, where transitions between counterpropagating Bloch fronts may spontaneously occur. The kinematic equations consist of coupled integro-differential equations for the front curvature and the front velocity, the order parameter associated with the NIB bifurcation. They capture the NIB bifurcation, the instabilities of Ising and Bloch fronts to transverse perturbations, the core structure of a spiral wave, and the dynamic process of spiral wave nucleation.Comment: 20 pages. Aric Hagberg: http://cnls.lanl.gov/~aric; Ehud Meron:http://www.bgu.ac.il/BIDR/research/staff/meron.htm

Kinematic Equations for Front Motion and Spiral-Wave Nucleation

We present a new set of kinematic equations for front motion in bistable media. The equations extend earlier kinematic approaches by coupling the front curvature with the order parameter associated with a parity breaking front bifurcation. In addition to naturally describing the core region of rotating spiral waves the equations can be be used to study the nucleation of spiral-wave pairs along uniformly propagating fronts. The analysis of spiral-wave nucleation reduces to the simpler problem of droplet, or domain, nucleation in one space dimension.Comment: 8 pages. Aric Hagberg: http://cnls.lanl.gov/~aric; Ehud Meron: http://www.bgu.ac.il/BIDR/research/staff/meron.htm

Cereal price instability in Ethiopia: An examination of sources and policy options

Managing food price instability is a long standing policy challenge, which, with mixed experiences of agricultural price policy reforms, has re-emerged as a contemporary policy issue. This is particularly true for Ethiopia, where managing food price stability continues to be a formidable policy challenge. The objective of this paper is to examine the underlying causes of cereal price instabilities and to assess the policy options to manage them. It undertakes three tasks: (a) analyzes the sources and degree of cereal price instability, (b) discusses the viability of various policy options, and (c) critically reviews the country’s past, ongoing, and emerging policies for food price stabilization. The results show that the determinants of price stability—infrastructure, information, and institutions—are at low levels of development; both production and price variability are high, and despite this continued high variability in prices, price risks mitigation has lost its importance in the country’s policy agenda. By analyzing market-based and non market-based policy options, as well as recent trends in the cereal markets, the paper argues and concludes that reliance on any single option may not produce the expected results. A combination of the two will be desirable, especially in the short run.Cereal, Policy, Price instability, Ethiopia, Agricultural and Food Policy, Community/Rural/Urban Development, Crop Production/Industries, Environmental Economics and Policy, Food Consumption/Nutrition/Food Safety, Food Security and Poverty, Institutional and Behavioral Economics, International Relations/Trade, Production Economics, Research and Development/Tech Change/Emerging Technologies, Research Methods/ Statistical Methods,