A Message from the Director

Latin American Studie

Pneumoccal Hemolysin

The purposes of this report are to describe a method of preparing a potent crude pneumococcal hemolysin, to define some of it characteristics, and to describe the effects of its administration to rabbits

SUPPLY RELATIONSHIPS IN THE SOUTH - WHAT HAVE WE LEARNED?

Industrial Organization,

DISCUSSION OF AGRICULTURAL ECONOMICS AND THE CHANGING STRUCTURE OF HIGHER EDUCATION

Teaching/Communication/Extension/Profession,

Effects of Fermion Flavor on Exciton Condensation in Double Layer Systems

We use fermionic path integral quantum Monte Carlo to study the effects of fermion flavor on the physical properties of dipolar exciton condensates in double layer systems. We find that by including spin in the system weakens the effective interlayer interaction strength, yet this has very little effect on the Kosterlitz-Thouless transition temperature. We further find that, to obtain the correct description of screening, it is necessary to account for correlation in both the interlayer and intralayer interactions. We show that while the excitonic binding cannot completely surpress screening by additional fermion flavors, their screening effectiveness is reduced leading to a much higher transition temperatures than predicted with large-N analysis.Comment: 4 pages, 3 figure

RECENT DUALITY CONTRIBUTIONS IN PRODUCTION ECONOMICS

This article is a limited assessment of the agricultural production economics literature since 1982 that resulted from dual modeling approaches. Contributions have removed several perceived obstacles to dual modeling, such as testing curvature, identifying the technology when prices are collinear, and examining dynamics of production. Some contributions have also removed obstacles to primal modeling. Dual methods have been used in risk applications only recently and still appear less convenient than primal methods. Convenience may become the primary criterion for selecting primal or dual methods.Production Economics,

DERIVED DEMAND FOR IRRIGATION WATER: THE CALIFORNIA AQUEDUCT

Resource /Energy Economics and Policy,

Estimation of trend in state-space models: Asymptotic mean square error and rate of convergence

The focus of this paper is on trend estimation for a general state-space model $Y_t=\mu_t+\varepsilon_t$, where the $d$th difference of the trend $\{\mu_t\}$ is assumed to be i.i.d., and the error sequence $\{\varepsilon_t\}$ is assumed to be a mean zero stationary process. A fairly precise asymptotic expression of the mean square error is derived for the estimator obtained by penalizing the $d$th order differences. Optimal rate of convergence is obtained, and it is shown to be "asymptotically equivalent" to a nonparametric estimator of a fixed trend model of smoothness of order $d-0.5$. The results of this paper show that the optimal rate of convergence for the stochastic and nonstochastic cases are different. A criterion for selecting the penalty parameter and degree of difference $d$ is given, along with an application to the global temperature data, which shows that a longer term history has nonlinearities that are important to take into consideration.Comment: Published in at http://dx.doi.org/10.1214/08-AOS675 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Path Integral Monte Carlo Simulations for Fermion Systems: Pairing in the Electron-Hole Plasma

We review the path integral method wherein quantum systems are mapped with Feynman's path integrals onto a classical system of "ring-polymers" and then simulated with the Monte Carlo technique. Bose or Fermi statistics correspond to possible "cross-linking" of polymers. As proposed by Feynman, superfluidity and Bose condensation result from macroscopic exchange of bosons. To map fermions onto a positive probability distribution, one must restrict the paths to lie in regions where the fermion density matrix is positive. We discuss a recent application to the two-component electron-hole plasma. At low temperature excitons and bi-excitons form. We have used nodal surfaces incorporating paired fermions and see evidence of a Bose condensation in the energy, specific heat and superfluid density. In the restricted path integral picture, pairing appears as intertwined electron-hole paths. Bose condensation occurs when these intertwined paths wind around the periodic boundaries.Comment: 14 pages, 7 figures Prepared for the 1999 International Conference on Strongly Coupled Coulomb Systems, Saint-Malo, Franc