Economics of Cocoa Production

Cocoa production is important to economic growth and the welfare of rural populations. Economic policy is oriented toward encouraging production, maintaining a stable cocoa price, and using cocoa sales as a source of tax revenue and foreign exchange. This chapter will concentrate on the economics of production-related issues at the farm, industry, and government levels. Special emphasis is given to constraints on the decision-making process of the cocoa producer, as well as to the existing knowledge on cocoa production economics. Rather than providing a systematic framework for decisions in cocoa production, we will consider economic insights into specific problems. The former information can be obtained from basic texts on farm management. A summary of the research evidence on specific cocoa production problems is less readily available

Twist operator correlation functions in O(n) loop models

Using conformal field theoretic methods we calculate correlation functions of geometric observables in the loop representation of the O(n) model at the critical point. We focus on correlation functions containing twist operators, combining these with anchored loops, boundaries with SLE processes and with double SLE processes. We focus further upon n=0, representing self-avoiding loops, which corresponds to a logarithmic conformal field theory (LCFT) with c=0. In this limit the twist operator plays the role of a zero weight indicator operator, which we verify by comparison with known examples. Using the additional conditions imposed by the twist operator null-states, we derive a new explicit result for the probabilities that an SLE_{8/3} wind in various ways about two points in the upper half plane, e.g. that the SLE passes to the left of both points. The collection of c=0 logarithmic CFT operators that we use deriving the winding probabilities is novel, highlighting a potential incompatibility caused by the presence of two distinct logarithmic partners to the stress tensor within the theory. We provide evidence that both partners do appear in the theory, one in the bulk and one on the boundary and that the incompatibility is resolved by restrictive bulk-boundary fusion rules.Comment: 18 pages, 8 figure

Reproducible Acoustic Emission Signatures by Indentation in Steels

Creating reproducible signals from defects is of great importance for quantitative studies of acoustic emission (AE). A method of doing so is presented here which consists of indentation of hardened steel plates. A survey was made of a variety of steels, including A533B pressure vessel steel with an embrittled weld as well as embrittled Wl, 01 and 02 tool steels. Regions in these steels with a Rockwell C hardness greater than about 50 produced detectable AE during indentation. In many cases the signals were reproducible over an appreciable range and appeared to be the same for epicenter measurements as those produced by sudden unloading. However, monitoring on the same surface as the crack in some cases produced sets of two different but reproducible signals which gradually evolved with repeated loading which could be due to crack branching or zigzag motion. Regions in the steels with a hardness less than about 40 on the Rockwell C scale produced no detectable AE, even with appreciable plastic deformation. Examination with scanning electron microscopy indicated that the AE signals were produced by the nucleation and incremental growth of subsurface cracks, generally penny-shaped, less than a millimeter in size. A typical fracture toughness value for such cracks in an embrittled 02 tool steel was calculated to be about 19MNm-3/2. AE was also produced in as-received A533B steel by indentation fatique. The method suggests itself for materials studies of AE as well as a nondestructive method for in situ examination of structures for embrittlement

The Effect of Convection on a Propagating Front with a Liquid Product: Comparison of Theory and Experiments

This work is devoted to the investigation of propagating polymerization fronts converting a liquid monomer into a liquid polymer. We consider a simplified mathematical model which consists of the heat equation and equation for the depth of conversion for one-step chemical reaction and of the Navier-Stokes equations under the Boussinesq approximation. We fulfill the linear stability analysis of the stationary propagating front and find conditions of convective and thermal instabilities. We show that convection can occur not only for ascending fronts but also for descending fronts. Though in the latter case the exothermic chemical reaction heats the cold monomer from above, the instability appears and can be explained by the interaction of chemical reaction with hydrodynamics. Hydrodynamics changes also conditions of the thermal instability. The front propagating upwards becomes less stable than without convection, the front propagating downwards more stable. The theoretical results are compared with experiments. The experimentally measured stability boundary for polymerization of benzyl acrylate in dimethyl formamide is well approximated by the theoretical stability boundary. (C) 1998 American Institute of Physics

Approach to Acoustic Emission Signal Analysis - Theory and Experiment

Acoustic Emission (AE) signals are notorious for their complexity and irreproducibility. Because AE source characteristics are virtually unknown and because the detected AE signals are colored by the propagation media, the sensor response and the instrumentation set tings, interpretations of test results such as spectral analysis or correlation studies are mostly qualitative and sometimes controversial; theories either are empirically derived or cannot be verified by experiments . In this paper, we sketch an approach to the AE signal analysis problem. We first report the development of a theory which allows the computation of the displacement as a function of time at an arbitrary ·point on an infinite plate due to an arbitrary point source force function . The theory is based on a new Fourier inversion technique which yields exact formulas similar to those developed for seismological ray theories. We then report experimental results obtained on a 2. 52 em thick aluminum plate using a reproducible step function stress release pulse as a simulated AE signal and a wide band displacement capacitive transducer as a sensor. The measurements are in quantitative agreement with the predictions of theory. We also discuss applications wherein the simulated signal, capacitive transducer and plate theory are used for AE source signature analysis, and sensor calibration problems

Experimental transmission of atypical scrapie to sheep

<p>Abstract</p> <p>Background</p> <p>Active surveillance for transmissible spongiform encephalopathies in small ruminants has been an EU regulatory requirement since 2002. A number of European countries have subsequently reported cases of atypical scrapie, similar to previously published cases from Norway, which have pathological and molecular features distinct from classical scrapie. Most cases have occurred singly in flocks, associated with genotypes considered to be more resistant to classical disease. Experimental transmissibility of such isolates has been reported in certain ovinised transgenic mice, but has not previously been reported in the natural host. Information on the transmissibility of this agent is vital to ensuring that disease control measures are effective and proportionate.</p> <p>Results</p> <p>This report presents the successful experimental transmission, in 378 days, of atypical scrapie to a recipient sheep of homologous genotype with preservation of the pathological and molecular characteristics of the donor. This isolate also transmitted to ovinised transgenic mice (Tg338) with a murine phenotype indistinguishable from that of Nor 98.</p> <p>Conclusion</p> <p>This result strengthens the opinion that these cases result from a distinct strain of scrapie agent, which is potentially transmissible in the natural host under field conditions.</p