FAPRI 2002 World Agricultural Outlook

Crop Production/Industries, Livestock Production/Industries,

Modeling DNA Structure, Elasticity and Deformations at the Base-pair Level

We present a generic model for DNA at the base-pair level. We use a variant of the Gay-Berne potential to represent the stacking energy between neighboring base-pairs. The sugar-phosphate backbones are taken into account by semi-rigid harmonic springs with a non-zero spring length. The competition of these two interactions and the introduction of a simple geometrical constraint leads to a stacked right-handed B-DNA-like conformation. The mapping of the presented model to the Marko-Siggia and the Stack-of-Plates model enables us to optimize the free model parameters so as to reproduce the experimentally known observables such as persistence lengths, mean and mean squared base-pair step parameters. For the optimized model parameters we measured the critical force where the transition from B- to S-DNA occurs to be approximately $140{pN}$. We observe an overstretched S-DNA conformation with highly inclined bases that partially preserves the stacking of successive base-pairs.Comment: 15 pages, 25 figures. submitted to PR

Physics of Solar Prominences: II - Magnetic Structure and Dynamics

Observations and models of solar prominences are reviewed. We focus on non-eruptive prominences, and describe recent progress in four areas of prominence research: (1) magnetic structure deduced from observations and models, (2) the dynamics of prominence plasmas (formation and flows), (3) Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and large-scale patterns of the filament channels in which prominences are located. Finally, several outstanding issues in prominence research are discussed, along with observations and models required to resolve them.Comment: 75 pages, 31 pictures, review pape

Two photons into \pi^0\pi^0

We perform a theoretical study based on dispersion relations of the reaction \gamma\gamma\to \pi^0\pi^0 emphasizing the low energy region. We discuss how the f_0(980) signal emerges in \gamma\gamma\to \pi\pi within the dispersive approach and how this fixes to a large extent the phase of the isoscalar S-wave \gamma\gamma\to \pi\pi amplitude above the K\bar{K} threshold. This allows us to make sharper predictions for the cross section at lower energies and our results could then be used to distinguish between different \pi\pi isoscalar S-wave parameterizations with the advent of new precise data on \gamma\gamma\to\pi^0\pi^0. We compare our dispersive approach with an updated calculation employing Unitary Chiral Perturbation Theory (U\chiPT). We also pay special attention to the role played by the \sigma resonance in \gamma\gamma\to\pi\pi and calculate its coupling and width to gamma\gamma, for which we obtain \Gamma(\sigma\to\gamma\gamma)=(1.68\pm 0.15) KeV.Comment: 31 pages, 9 figure

ʻConodont pearlsʼ do not belong to conodonts

We investigated the mineralogical and chemical signatures of enigmatic microspherules commonly recovered in conodont residues and referred to in literature as ‘conodont pearls.’ Comparison between these ‘pearls,’ associated conodonts and other phosphatic skeletal elements present in the same stratigraphical level was run in an effort to reveal any possible relation between ‘conodont pearls’ and the joined groups so to finally provide a response on the affinity of these spherules

INTERNAL COMPETITION OVER FOREIGN POLICY-MAKING: THE CASE OF U.S. ARMS SALES TO IRAN

Two models of foreign-policy making, the bureaucratic politics model and the royal court model, are helpful in explaining U.S. arms sales to Iran in 1985 and in 1986. The bureaucratic politics model is particularly useful in clarifying both the positions taken by the leaders of the foreign policy bureaucracy to the arms sales proposals and the behavior of these officials as the sales were implemented. However, the royal court model best ac- counts for the decisive role of the president and the deference given to those advisers perceived to be acting in his interests. Copyright 1990 by The Policy Studies Organization.