How policy changes affected cocoa sectors in sub-Saharan African countries

Structural adjustment programs in sub-Saharan African countries in the 1980s removed trade restrictions, price controls, and export taxes and abolished state-owned commodity marketing bodies. The authors studied the effects of these policy changes on the coca sector, using a global econometric model specifying major producer countries through the vintage-capital approach. They focused on Ghana and Nigeria (major cocoa producers that undertook structural adjustment programs), as well as on Cote d'Ivoire and Cameroon. The impact on world cocoa prices of structural adjustment programs in Ghana and Nigeria was relatively small. The results imply that, without structural adjustment programs in Ghana and Nigeria, world cocoa prices in the late 1980s would have been about US$1,060/ton (in 1985 constant dollars), instead of US$850/ton. So, without the structural adjustment programs, 1989-90 world prices in real terms would have been about 45 percent lower than they were in the early 1980s, compared with an actual decline of 55 percent. Much more important in depressing prices in this period was the rapid increase in production in Brazil, Cote d'Ivoire, Indonesia, and Malaysia (which together accounted for about 75 percent of the increased production in that decade). That increased production resulted largely from tree planting in response to higher world cocoa prices in the late 1970s -- and subsequent increases in productivity. The results of counterfactual simulations suggest that cocoa production in Ghana would have been at almost half its 1989-90 level if Ghana had not implemented its structural adjustment program. The producers'surplus would have been lower without the program, and the government's budget deficit would have been unsustainable. The effects of the structural adjustment program in Nigeria are mixed. The simulation results show lower cocoa production but higher government revenue without the reforms. But the program was evaluated only three years after the reforms, so the full effects on production had not been realized. The structural adjustment programs in Ghana and Nigeria had a negative effect on other cocoa-producing countries in sub-Saharan Africa and the rest of the world -- producing an estimated loss (in government revenue from cocoa exports and producer surplus) of about 15 percent in other sub-Saharan African countries. Results show that both Cote d'Ivoire and Cameroon would have been better off had they set export taxes at a higher level (closer to an estimated"optimal"level) at the same time that they depreciated the real exchange rate. Producer prices could have been sustained at their earlier higher level, or even raised, without hurting government revenues. Structural adjustment programs in Ghana and Nigeria had a negative effect on producers in other countries, but not adopting such policies would have been economically irrational, contend the authors.Environmental Economics&Policies,Economic Theory&Research,Economic Stabilization,Access to Markets,Markets and Market Access

Time-dependent gravitating solitons in five dimensional warped space-times

Time-dependent soliton solutions are explicitly derived in a five-dimensional theory endowed with one (warped) extra-dimension. Some of the obtained geometries, everywhere well defined and technically regular, smoothly interpolate between two five-dimensional anti-de Sitter space-times for fixed value of the conformal time coordinate. Time dependent solutions containing both topological and non-topological sectors are also obtained. Supplementary degrees of freedom can be also included and, in this case, the resulting multi-soliton solutions may describe time-dependent kink-antikink systems.Comment: 19 pages, 10 figure

Universal Properties of Two-Dimensional Boson Droplets

We consider a system of N nonrelativistic bosons in two dimensions, interacting weakly via a short-range attractive potential. We show that for N large, but below some critical value, the properties of the N-boson bound state are universal. In particular, the ratio of the binding energies of (N+1)- and N-boson systems, B_{N+1}/B_N, approaches a finite limit, approximately 8.567, at large N. We also confirm previous results that the three-body system has exactly two bound states. We find for the ground state B_3^(0) = 16.522688(1) B_2 and for the excited state B_3^(1) = 1.2704091(1) B_2.Comment: 4 pages, 2 figures, final versio

Vacuum Decay in Theories with Symmetry Breaking by Radiative Corrections

The standard bounce formalism for calculating the decay rate of a metastable vacuum cannot be applied to theories in which the symmetry breaking is due to radiative corrections, because in such theories the tree-level action has no bounce solutions. In this paper I derive a modified formalism to deal with such cases. As in the usual case, the bubble nucleation rate may be written in the form $A e^{-B}$. To leading approximation, $B$ is the bounce action obtained by replacing the tree-level potential by the leading one-loop approximation to the effective potential, in agreement with the generally adopted {\it ad hoc} remedy. The next correction to $B$ (which is proportional to an inverse power of a small coupling) is given in terms of the next-to-leading term in the effective potential and the leading correction to the two-derivative term in the effective action. The corrections beyond these (which may be included in the prefactor) do not have simple expressions in terms of the effective potential and the other functions in the effective action. In particular, the scalar-loop terms which give an imaginary part to the effective potential do not explicitly appear; the corresponding effects are included in a functional determinant which gives a manifestly real result for the nucleation rate.Comment: 39 pages, CU-TP-57

Gravitating multidefects from higher dimensions

Warped configurations admitting pairs of gravitating defects are analyzed. After devising a general method for the construction of multidefects, specific examples are presented in the case of higher-dimensional Einstein-Hilbert gravity. The obtained profiles describe diverse physical situations such as (topological) kink-antikink systems, pairs of non-topological solitons and bound configurations of a kink and of a non-topological soliton. In all the mentioned cases the geometry is always well behaved (all relevant curvature invariants are regular) and tends to five-dimensional anti-de Sitter space-time for large asymptotic values of the bulk coordinate. Particular classes of solutions can be generalized to the framework where the gravity part of the action includes, as a correction, the Euler-Gauss-Bonnet combination. After scrutinizing the structure of the zero modes, the obtained results are compared with conventional gravitating configurations containing a single topological defect.Comment: 27 pages, 5 included figure

Transforming to Lorentz Gauge on de Sitter

We demonstrate that certain gauge fixing functionals cannot be added to the action on backgrounds such as de Sitter in which a linearization instability is present. We also construct the field dependent gauge transformation which carries the electromagnetic vector potential from a convenient, non-de Sitter invariant gauge to the de Sitter invariant, Lorentz gauge. The transformed propagator agrees with the de Sitter invariant result previously found by solving the propagator equation in Lorentz gauge. This shows that the gauge transformation technique will eliminate unphysical breaking of de Sitter invariance introduced by a gauge condition. It is suggested that the same technique can be used to finally resolve the issue of whether or not free gravitons are de Sitter invariant.Comment: 45 page

Continued evaluation of potential for geologic storage of carbon dioxide in the southeastern United States

Southern States Energy Board Duke Energy Santee Cooper Power Southern CompanyBureau of Economic Geolog

Direct Numerical Simulation of Turbulent Couette-Poiseuille Flow With Zero Skin Friction

The near-wall scaling of mean velocity U(yw) is addressed for the case of zero skin friction on one wall of a fully turbulent channel flow. The present DNS results can be added to the evidence in support of the conjecture that U is proportional to the square root of yw in the region just above the wall at which the mean shear dU=dy = 0

Decays of metastable vacua in SQCD

The decay rates of metastable SQCD vacua in ISS-type models, both towards supersymmetric vacua as well as towards other nonsupersymmetric configurations arising in theories with elementary spectators, are estimated numerically in the semiclassical approximation by computing the corresponding multifield bounce configurations. The scaling of the bounce action with respect to the most relevant dimensionless couplings and ratios of scales is analyzed. In the case of the decays towards the susy vacua generated by nonperturbative effects, the results confirm previous analytical estimations of this scaling, obtained by assuming a triangular potential barrier. The decay rates towards susy vacua generated by R-symmetry breaking interactions turn out to be more than sufficiently suppressed for the phenomenologically relevant parameter range, and their behavior in this regime differs from analytic estimations valid for parametrically small scale ratios. It is also shown that in models with spectator fields, even though the decays towards vacua involving nonzero spectator VEVs don't have a strong parametric dependence on the scale ratios, the ISS vacuum can still be made long-lived in the presence of R-symmetry breaking interactions.Comment: 22 pages, 7 figure