Price expectations and price dynamics: the case of the rice sector in developing Asia

Uncertainty is a crucial issue for producers who must make input decisions without knowing prices and without perfect knowledge of realized output. In this context, price expectations strongly determine the production choices and market prices that result from market-clearing conditions. This study analyzed the role that price expectations play in price dynamics, developing a theoretical model of trade in varieties following Armington (1969) and augmented with yield and price uncertainty to highlight several main determinants of domestic producer prices, including exchange rates, proximity to world markets, input prices, natural disasters, and producers' expectations. An econometric estimation of the rice sector, using a panel of 13 developing Asian countries during 1965-2003, confirmed that expectations count, with a 1% increase in the expected price resulting in a 1.18% decrease in the market price. A simulation exercise based on these empirical results demonstrated that forecasting errors are large. Specifically, Asian rice farmers have a 50% chance of making prediction errors of 10% or more on the final market price. This high error rate suggests the need for developing ways of sharing information, such as radio programs dedicated to agricultural producers or the introduction of futures markets, to stabilize agricultural incomes.Rice ; Asia ; price dynamics ; price expectations ;

Classical Heisenberg spins with long-range interactions: Relaxation to equilibrium for finite systems

Systems with long-range interactions often relax towards statistical equilibrium over timescales that diverge with $N$, the number of particles. A recent work [S. Gupta and D. Mukamel, J. Stat. Mech.: Theory Exp. P03015 (2011)] analyzed a model system comprising $N$ globally coupled classical Heisenberg spins and evolving under classical spin dynamics. It was numerically shown to relax to equilibrium over a time that scales superlinearly with $N$. Here, we present a detailed study of the Lenard-Balescu operator that accounts at leading order for the finite-$N$ effects driving this relaxation. We demonstrate that corrections at this order are identically zero, so that relaxation occurs over a time longer than of order $N$, in agreement with the reported numerical results.Comment: 20 pages, 3 figures; v2: minor changes, published versio

Overemployment, Underemployment and the opportunity cost of time

Focusing on individual labor market positions, this article proposes a new approach to elicit and measure constraints faced by rural households. Under market imperfections, individuals fail to equalize their hourly income to their shadow wage and become over- or underemployed. We estimate and explain this gap in a stochastic frontier framework for rural Vietnam. Both employees and farmers are found to fail in equalizing their hourly income to their shadow wage. Constraints faced by farmers are found to be stronger than that of employees: farmers' marginal revenue of labor is 3 times higher than their shadow wage while market wages earned by employees are 1.5 times higher than their shadow wages. Price risk is found to be the most important constraint faced by Vietnamese rural farmers while employees would benefit from the development of the road network.Market imperfections ; Shadow wages ; Allocative efficiency ; Vietnam

The 4-string Braid group B4B_4 has property RD and exponential mesoscopic rank

We prove that the braid group $B_4$ on 4 strings, as well as its central quotient $B_4/$, have the property RD of Haagerup-Jolissaint. It follows that the automorphism group \Aut(F_2) of the free group $F_2$ on 2 generators has property RD. We also prove that the braid group $B_4$ is a group of intermediate rank (of dimension 3). Namely, we show that both $B_4$ and its central quotient have exponential mesoscopic rank, i.e., that they contain exponentially many large flat balls which are not included in flats.Comment: reference added, minor correction

Bifurcations and singularities for coupled oscillators with inertia and frustration

We prove that any non zero inertia, however small, is able to change the nature of the synchronization transition in Kuramoto-like models, either from continuous to discontinuous, or from discontinuous to continuous. This result is obtained through an unstable manifold expansion in the spirit of J.D. Crawford, which features singularities in the vicinity of the bifurcation. Far from being unwanted artifacts, these singularities actually control the qualitative behavior of the system. Our numerical tests fully support this picture.Comment: 10 pages, 2 figure

Microcanonical solution of lattice models with long range interactions

We present a general method to obtain the microcanonical solution of lattice models with long range interactions. As an example, we apply it to the long range Ising chain, focusing on the role of boundary conditions.Comment: 6 pages, proceedings of the NEXT 2001 conferenc