General Equilibrium Effects in the South African Maize Market: International Trade Simulations

Following deregulation in the 1990's the South African maize producing industry has been suffering a gradual decline. Current low prices suggest that this trend may continue or worsen. This paper discusses the results from a static general equilibrium model for the South African economy to evaluate the effects on the economy. The analysis covers summer cereals producing agricultural regions, production in other sectors in the economy, commodity markets and the economy at large. Additionally, the effects on factors, households and the government are analysed. The first set of experiments is aimed to evaluate the effects of an increase in import tariffs on summer cereals. The results indicate that under normal conditions South Africa will experience little effect for even relatively large increases in the tariff rate, which follows from the fact that South Africa does not currently import sizeable quantities of maize. The second set of experiments evaluate the effects of a change in world prices of summer cereals, under the presumption that a reduction in levels of producer support in developed countries may lead to increased world prices. The results indicate that this terms-of-trade improvement does not necessarily lead to benefits to all in the economy. Benefits to summer cereals producers are largely offset by losses in other sectors of the economy, for example producers of livestock, though the overall effect is still positive.International Relations/Trade,

The Impact of a Higher Fuel Levy on the Western Cape

The Western Cape Provincial Government's proposal to introduce a provincial fuel levy within a band of 10 and 50 cents per litre raises concerns on the impact this may have on the economy, especially at a time of high international oil prices. This study reports the results of a computable general equilibrium (CGE) analysis of the impact of higher tax rates on petroleum products on the economy, with specific focus on prices, employment and household expenditure. The results show that increasing the tax rate on petroleum products results in higher petroleum prices, which again put upward pressure on intermediate input costs. Households in the Western Cape will experience a decrease in per capita expenditure, as unemployment increases and returns to factors employed decrease. The impact is however very small. The impacts on agricultural activities differ among regions, but the net effect is a contraction in agricultural output.Resource /Energy Economics and Policy,

A Computable General Equilibrium (CGE) Analysis of the Impact of an Oil Price Increase in South Africa

Following recent international oil price increases, there has been considerable interest in how this external factor can affect the South African economy. This paper reports results from a computable general equilibrium (CGE) analysis of an increase (up to 30 per cent) in international oil prices. Background information is provided, which puts the magnitude of the price variations in historical context. We describe the procedure used to adjust the social accounting matrix (SAM), which is used to calibrate the model, to account explicitly for crude oil. Then, the effects of the crude oil price increase are traced through the economy, from markets, industries through to factors, households and the government. Predictably, the shock hurts the economy: a 20 per cent increase results in a drop in GDP of 1 per cent. It is found that the major impact is to be found in the petroleum industry itself, whereas the effects on liquid fuel dependent industries such as transport is not as large as may be supposed. In agriculture, it is found that the depreciating currency has a positive effect, offsetting most of the negative effects of higher petroleum prices, particularly in export-oriented areas. In a long-term scenario, capital and skilled labour becomes mobile, and the results suggest that such reallocation may not be to the overall advantage of the economy.Resource /Energy Economics and Policy,

Primary crustal melt compositions: Insights into the controls, mechanisms and timing of generation from kinetics experiments and melt inclusions

We explore the controls, mechanisms and timing of generation of primary melts and their compositions, and show that the novel studies of melt inclusions in migmatites can provide important insights into the processes of crustal anatexis of a particular rock. Partial melting in the source region of granites is dependent on five main processes: (i) supply of heat; (ii) mineral–melt interface reactions associated with the detachment and supply of mineral components to the melt, (iii) diffusion in the melt, (iv) diffusion in minerals, and (v) recrystallization of minerals. As the kinetics of these several processes vary over several orders of magnitude, it is essential to evaluate in Nature which of these processes control the rate of melting, the composition of melts, and the extent to which residue–melt chemical equilibrium is attained under different circumstances. To shed light on these issues, we combine data from experimental and melt inclusion studies. First, data from an extensive experimental program on the kinetics of melting of crustal protoliths and diffusion in granite melt are used to set up the necessary framework that describes how primary melt compositions are established during crustal anatexis. Then, we use this reference frame and compare compositional trends from experiments with the composition of melt inclusions analyzed in particular migmatites. We show that, for the case of El Hoyazo anatectic enclaves in lavas, the composition of glassy melt inclusions provides important information on the nature and mechanisms of anatexis during the prograde suprasolidus history of these rocks, including melting temperatures and reactions, and extent of melt interconnection, melt homogenization and melt–residue equilibrium. Compositional trends in several of the rehomogenized melt inclusions in garnet from migmatites/granulites in anatectic terranes are consistent with diffusion in melt-controlled melting, though trace element compositions of melt inclusions and coexisting minerals are necessary to provide further clues on the nature of anatexis in these particular rocks.This work was supported by the National Science Foundation [grants EAR-9603199, EAR-9618867, EAR-9625517 and EAR-9404658], the Italian Consiglio Nazionale delle Ricerche, the European Commission (grant 01-LECEMA22F through contract No. ERAS-CT-2003-980409; and a H2020 Marie Skłodowska-Curie Actions under grant agreement No. 654606), the Italian Ministry of Education, University and Research (grants PRIN 2007278A22, 2010TT22SC and SIR RBSI14Y7PF), the Università degli Studi di Padova [Progetto di Ateneo CPDA107188/10 and a Piscopia—Marie Curie Fellowship under grant agreement No. 600376], the Australian Research Council (Australian Professorial Fellowship and Discovery Grants Nos. DP0342473 and DP0556700), and the National Research Foundation (South Africa; Incentives For Rated Researchers Program)

SeeResults: A Spreadsheet Application for the Analysis of CGE Model Results

CGE models tend to produce large amounts of result data, and it can be difficult and timeconsuming to view, import, process and keep track of these. SeeResults is an Excel-based spreadsheet application that has been developed within the PROVIDE project to facilitate viewing results and producing presentation output, such as charts. It effectively functions as a GDX (a binary format used for output from GAMS) file viewer, and has been designed to be flexible, user-friendly and immediately usable with minimal configuration. This paper describes the rationale for the application, its main features, a number of screen captures and implementation notes.Research and Development/Tech Change/Emerging Technologies,

Chemical diffusion of fluorine in melts in the system Na2OAl2O3SiO2

The volatilization of fluorine from three melts in the system Na2OAl2O3SiO2 has been investigated at 1 atm pressure and 1200–1400°C. The melts chosen have base compositions corresponding to albite, jadeite and a peraluminous melt with 75 mole % SiO2. Melt spheres were suspended from platinum loops in a vertical tube furnace in a flow of oxygen gas, then quenched, sectioned and analysed by electron microprobe. The microprobe scans indicate that transport of fluorine to the melt-vapor interface is by binary, concentration-independent interdiffusion of fluorine and oxygen. FO interdiffusivity increases in the order albite < peraluminous < jadeite. There is no simple reciprocal relationship between FO interdiffusivity and melt viscosity. Comparison with data on high-pressure interdiffusivity of fluorine and oxygen in jadeite melt indicates that FO interdiffusivity increases with pressure from 0.001 to 10 kbar while the activation energy remains unchanged. Fluorine chemical diffusivity in albite melt is substantially lower than H2O chemical diffusivity in obsidian melts suggesting that different diffusive mechanisms are responsible for the transport of F and H2O in igneous melts. Fluorine diffuses in albite melt via an anionic exchange with oxygen whereas water probably diffuses in obsidian melt via an alkali exchange mechanism

Influence of melt feeding scheme and casting parameters during direct-chill casting on microstructure of an AA7050 billet

© The Minerals, Metals & Materials Society and ASM International 2012Direct-chill (DC) casting billets of an AA7050 alloy produced with different melt feeding schemes and casting speeds were examined in order to reveal the effect of these factors on the evolution of microstructure. Experimental results show that grain size is strongly influenced by the casting speed. In addition, the distribution of grain sizes across the billet diameter is mostly determined by melt feeding scheme. Grains tend to coarsen towards the center of a billet cast with the semi-horizontal melt feeding, while upon vertical melt feeding the minimum grain size was observed in the center of the billet. Computer simulations were preformed to reveal sump profiles and flow patterns during casting under different melt feeding schemes and casting speeds. The results show that solidification front and velocity distribution of the melt in the liquid and slurry zones are very different under different melt feeding scheme. The final grain structure and the grain size distribution in a DC casting billet is a result of a combination of fragmentation effects in the slurry zone and the cooling rate in the solidification range

A Numerical Treatment of Melt/Solid Segregation: Size of the Eucrite Parent Body and Stability of the Terrestrial Low-Velocity Zone

Crystal sinking to form cumulates and melt percolation toward segregation in magma pools can be treated with modifications of Stokes' and Darcy's laws, respectively. The velocity of crystals and melt depends, among other things, on the force of gravity (g) driving the separations and the cooling time of the environment. The increase of g promotes more efficient differentiation, whereas the increase of cooling rate limits the extent to which crystals and liquid can separate. The rate at which separation occurs is strongly dependent on the proportion of liquid that is present. As a result, cumulate formation is a process with a negative feedback; the more densely aggregated the crystals become, the slower the process can proceed. In contrast, melt accumulation is a process with a positive feedback; partial accumulation of melt leads to more rapid accumulation of subsequent melt. This positive feedback can cause melt accumulation to run rapidly to completion once a critical stability limit is passed. The observation of cumulates and segregated melts among the eucrite meteorites is used as a basis for calculating the g (and planet size) required to perform these differentiations. The eucrite parent body was probably at least 10-100 km in radius. The earth's low velocity zone (LVZ) is shown to be unstable with respect to draining itself of excess melt if the melt forms an interconnecting network. A geologically persistent LVZ with a homogeneous distribution of melt can be maintained with melt fractions only on the order of 0.1% or less

Elastic properties of silicate melts: Implications for low velocity zones at the lithosphere-asthenosphere boundary.

Low seismic velocity regions in the mantle and crust are commonly attributed to the presence of silicate melts. Determining melt volume and geometric distribution is fundamental to understanding planetary dynamics. We present a new model for seismic velocity reductions that accounts for the anomalous compressibility of silicate melt, rendering compressional wave velocities more sensitive to melt fraction and distribution than previous estimates. Forward modeling predicts comparable velocity reductions for compressional and shear waves for partially molten mantle, and for low velocity regions associated with the lithosphere-asthenosphere boundary (LAB), melt present at &lt;5% distributed in near-textural equilibrium. These findings reconcile seismic observations for the LAB regionally and locally and favor models of strong coupling across the LAB rather than melt channeling due to shear deformation