The adding-up problem : strategies for primary commodity exports in sub-Saharan Africa

Many countries in sub-Saharan Africa remain dependent on a few primary commodities -- coffee, cocoa, cotton, sugar, tea, and tobacco -- for a large share of export earnings. Because demand for these commodities is price-inelastic, production and export expansion can depress world prices and hence reduce net export revenue. The authors discuss the effects of this phenomenon -- the adding-up problem -- on policy and development strategies for major agricultural export commodities in sub-Saharan Africa. They conclude that, as a practical matter, it is not feasible to design a regional commodity production and trade policy for sub-Saharan Africa as a whole because of the difficulty of equitably distributing the benefits of such a policy. Moreover, if an export tax is imposed on sub-Saharan Africa as a whole, the greatest benefits may go to producers in other regions such as Asia and Latin America. Individually, few countries in sub-Saharan Africa have sufficient market power to influence commodity prices in the long run. Possible expectations include Cote d'Ivoire (in cocoa) and to a lesser extent Ghana (in cocoa), Kenya (in tea), and Malawi (in burley tobacco). Export taxes may prove beneficial for these countries but, at certain levels, the primary effect of"optimal"taxes is to transfer resources from smallholders to governments with limited marginal welfare gains.Economic Theory&Research,Environmental Economics&Policies,Crops&Crop Management Systems,Access to Markets,Markets and Market Access

Commodity market reform in Africa : some recent experience

Since the early 1980s, dramatic changes in export commodity markets, shocks associated with resulting price declines, and changing views on the role of the state have ushered in widespread reforms to agricultural commodity markets in Africa. The reforms significantly reduced government participation in the marketing and pricing of commodities. Akiyama, Baffes, Larson, and Varangis examine the background, causes, process, and consequences of these reforms and derive lessons for successful reforms from experiences in markets for four commodities important to Africa-cocoa, coffee, cotton, and sugar. The authors'commodity focus highlights the special features associated with these markets that affect the reform process. They complement the current literature on market reforms in Africa, where grain-market studies are more common. The authors suggest that the types of market interventions prior to reform are more easily classified by crop than by country. Consequently, there are significant commodity-specific differences in the initial conditions and in the outcomes of reforms related to these markets. But there are general lessons as well. The authors find that the key consequences of reform have been significant changes in or emergence of marketing institutions and a significant shift of political and economic power from the public to the private sector. In cases where interventions were greatest and reforms most complete, producers have benefited from receiving a larger share of export prices. Additionally, the authors conclude that the adjustment costs of reform can be reduced in most cases by better understanding the detailed and idiosyncratic relationships between the commodity subsector, private markets, and public services. Finally, while there are significant costs to market-dependent reforms, experiences suggest that they are a necessary step toward a dynamic commodity sector based on private initiative. This is particularly true in countries and sectors where interventions were greatest and market-supporting institutions the weakest.Economic Theory&Research,Enterprise Development&Reform,Environmental Economics&Policies,Labor Policies,Markets and Market Access,Environmental Economics&Policies,Access to Markets,Markets and Market Access,Economic Theory&Research,Crops&Crop Management Systems

Metal-to-insulator transition in anatase TiO2 thin films induced by growth rate modulation

We demonstrate control of the carrier density of single phase anatase TiO2 thin films by nearly two orders of magnitude by modulating the growth kinetics during pulsed laser deposition, under fixed thermodynamic conditions. The resistivity and the intensity of the photoluminescence spectra of these TiO2 samples, both of which correlate with the number of oxygen vacancies, are shown to depend strongly on the growth rate. A quantitative model is used to explain the carrier density changes.Comment: 13 pages 3 figure

Gain in a quantum wire laser of high uniformity

A multi-quantum wire laser operating in the 1-D ground state has been achieved in a very high uniformity structure that shows free exciton emission with unprecedented narrow width and low lasing threshold. Under optical pumping the spontaneous emission evolves from a sharp free exciton peak to a red-shifted broad band. The lasing photon energy occurs about 5 meV below the free exciton. The observed shift excludes free excitons in lasing and our results show that Coulomb interactions in the 1-D electron-hole system shift the spontaneous emission and play significant roles in laser gain.Comment: 4 pages, 4 figures, prepared by RevTe

The aggregation of cytochrome C may be linked to its flexibility during refolding

Large-scale expression of biopharmaceutical proteins in cellular hosts results in production of large insoluble mass aggregates. In order to generate functional product, these aggregates require further processing through refolding with denaturant, a process in itself that can result in aggregation. Using a model folding protein, cytochrome C, we show how an increase in final denaturant concentration decreases the propensity of the protein to aggregate during refolding. Using polarised fluorescence anisotropy, we show how reduced levels of aggregation can be achieved by increasing the period of time the protein remains flexible during refolding, mediated through dilution ratios. This highlights the relationship between the flexibility of a protein and its propensity to aggregate. We attribute this behaviour to the preferential urea-residue interaction, over self-association between molecules

Spatial Relationship between Solar Flares and Coronal Mass Ejections

We report on the spatial relationship between solar flares and coronal mass ejections (CMEs) observed during 1996-2005 inclusive. We identified 496 flare-CME pairs considering limb flares (distance from central meridian > 45 deg) with soft X-ray flare size > C3 level. The CMEs were detected by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO). We investigated the flare positions with respect to the CME span for the events with X-class, M-class, and C-class flares separately. It is found that the most frequent flare site is at the center of the CME span for all the three classes, but that frequency is different for the different classes. Many X-class flares often lie at the center of the associated CME, while C-class flares widely spread to the outside of the CME span. The former is different from previous studies, which concluded that no preferred flare site exists. We compared our result with the previous studies and conclude that the long-term LASCO observation enabled us to obtain the detailed spatial relation between flares and CMEs. Our finding calls for a closer flare-CME relationship and supports eruption models typified by the CSHKP magnetic reconnection model.Comment: 7 pages; 4 figures; Accepted by the Astrophysical Journa

Tools for computing the AGN feedback: radio-loudness distribution and the kinetic luminosity function

We studied the Active Galactic Nuclei (AGN) radio emission from a compilation of hard X-ray selected samples, all observed in the 1.4 GHz band. A total of more than 1600 AGN with 2-10 keV de-absorbed luminosities higher than 10^42 erg/s were used. For a sub-sample of about 50 z\lsim 0.1 AGN it was possible to reach a ~80% fraction of radio detections and therefore, for the first time, it was possible to almost completely measure the probability distribution function of the ratio between the radio and the X-ray luminosity Rx=log[L(1.4)/Lx]. The probability distribution function of Rx was functionally fitted as dependent on the X-ray luminosity and redshift, P(Rx|Lx,z). It roughly spans over 6 decades (-7<Rx<-1), and does not show any sign of bi-modality. It resulted that the probability of finding large values of the Rx ratio increases with decreasing X-ray luminosities and (possibly) with increasing redshift. No statistical significant difference was found between the radio properties of the X-ray absorbed and unabsorbed AGN. The measure of the probability distribution function of Rx allowed us to compute the kinetic luminosity function and the kinetic energy density which, at variance with what assumed in many galaxy evolution models, is observed to decrease of about a factor of five at redshift below 0.5. About half of the kinetic energy density results to be produced by the more radio quiet (Rx<-4) AGN. In agreement with previous estimates, the AGN efficiency in converting the accreted mass energy into kinetic power is, on average, ~5x10-3.Comment: 13 pages, ApJsty; ApJ in pres