Rotating massive O stars with non-spherical 2D winds

We present solutions for the velocity field and mass-loss rates for 2D axisymmetric outflows, as well as for the case of mass accretion through the use of the Lambert W-function. For the case of a rotating radiation-driven wind the velocity field is obtained analytically using a parameterised description of the line acceleration that only depends on radius r at any given latitude $\theta$. The line acceleration g(r) is obtained from Monte-Carlo multi-line radiative transfer calculations. The critical/sonic point of our equation of motion varies with latitude $\theta$. Furthermore, an approximate analytical solution for the supersonic flow of a rotating wind is derived, which is found to closely resemble the exact solution. For the simultaneous solution of the mass-loss rate and velocity field, we use the iterative method of our 1D method extended to the non-spherical 2D case. We apply the new theoretical expressions with our iterative method to the stellar wind from a differentially rotating 40 $M_{sun}$ O5-V main sequence star as well as to a 60 $M_{sun}$ O-giant star, and we compare our results to previous studies that are extensions of the Castor et al. (1975, ApJ, 195, 157) CAK formalism. Next, we account for the effects of oblateness and gravity darkening. Our numerical results predict an equatorial decrease of the mass-loss rate, which would imply that (surface-averaged) total mass-loss rates are lower than for the spherical 1D case, in contradiction to the Maeder & Meynet (2000, A&A, 361, 159) formalism that is oftentimes employed in stellar evolution calculations for rotating massive stars. To clarify the situation in nature we discuss observational tests to constrain the shapes of large-scale 2D stellar winds.Comment: 20 pages, 4 figures, 7 tables, accepted for publication in A&A, (one corrected sentence in sect. 4.1.), a generalization of arXiv paper: arXiv:0810.190

THE AGRICULTURAL POTENTIAL OF SADC

Various institutions wanting to invest in agricultural production or the agribusiness sector in the SADC region need information on the quality and location of agricultural resources. Generating agricultural resource information on a regional level provides the challenge of integrating vast amounts of information from the various countries, implying storing, retrieving and manipulating it to determine areas best suited to grow a particular crop; or various crops that can be grown in a particular area. A Geographical Information System (GIS) has been developed as part of a broader project to assess the agricultural potential of SADC countries from a physical-biological-climatological point of view. Crop suitability maps obtained from the GIS containing information on resource quality, combined with transport modelling to add information on transport cost, can be used by private sector institutions for location decisions and the public sector for planning the provision of physical and social infrastructure. Incorporating resource data of the whole region implies that the available data on the climate, topography and soils of most of the SADC countries is coarse which only allows analyses on a national and regional level.International Development,

Comparative advantage of organic wheat production in the Western Cape

In a context in which the framework of agricultural policy and business is changing radically the objective of the government and farmers should be to support the development of systems that look likely to be winners in the future. As a result this paper uses a Policy Analysis Matrix (PAM) to determine whether wheat production would have a comparative advantage if produced under organic practices. The paper starts by analysing the comparative advantage of wheat under conventional practices, and later contrasts conventional with organic practices. The results of the analyses mainly indicate a comparative advantage for wheat grown under organic practices especially when the social cost benefit ratio (SCB) is incorporated into the analyses. This is because the domestic resource cost (DRC) criterion that is used by the PAM is confirmed to understate the social profitability of systems that use domestic factors intensively like organic wheat systems and favours systems that use less of these factors like conventional systems. The results also show the existence of distortions in the market even if wheat were to be produced under organic practises, although these are shown to be less than for wheat produced under conventional practices.Crop Production/Industries,

Dynamic System Adaptation by Constraint Orchestration

For Paradigm models, evolution is just-in-time specified coordination conducted by a special reusable component McPal. Evolution can be treated consistently and on-the-fly through Paradigm's constraint orchestration, also for originally unforeseen evolution. UML-like diagrams visually supplement such migration, as is illustrated for the case of a critical section solution evolving into a pipeline architecture.Comment: 19 page

Combining Insertion and Deletion in RNA-editing Preserves Regularity

Inspired by RNA-editing as occurs in transcriptional processes in the living cell, we introduce an abstract notion of string adjustment, called guided rewriting. This formalism allows simultaneously inserting and deleting elements. We prove that guided rewriting preserves regularity: for every regular language its closure under guided rewriting is regular too. This contrasts an earlier abstraction of RNA-editing separating insertion and deletion for which it was proved that regularity is not preserved. The particular automaton construction here relies on an auxiliary notion of slice sequence which enables to sweep from left to right through a completed rewrite sequence.Comment: In Proceedings MeCBIC 2012, arXiv:1211.347

FYNBOS EXPORTS FROM THE WESTERN CAPE PROVINCE: A PROBLEM OF LOGISTICS

During 1997 research was conducted on trends in factors that affect the supply and demand for airfreight space for fynbos exports from South Africa. The aim was to sensitise decision-makers to probable trends in those factors that will shape cargo space availability. The main finding was that the supply of airfreight to South African producers is aggravated by the unbalanced availability of cargo space on southbound and northbound trips originating from Cape Town. If the price and quantity of cargo space were determined by supply and demand, an imbalance couldn’t arise in a perfect market, as prices would balance cargo space supplied and demanded. However, airfreight tariffs are rigid per weight level. The result is that items with a higher mass per volume unit represent a higher income per palette, and are therefore preferred by export agents. This finding has implications for future growth in the industry.International Relations/Trade,

THE COMPETITIVENESS OF WESTERN CAPE WHEAT PRODUCTION: AN INTERNATIONAL COMPARISON

This paper reports the results of an international comparison of the cost of producing wheat in 8 Western Cape, 3 Free State and 7 foreign producing areas. Results show that South African yields are low compared to foreign countries whose production costs are as high as or higher than those in South Africa, while the net margins for South African producers are less than a third of those for countries that have the same or lower yields as South Africa. If the wheat industry in the Western Cape is to survive international competition, it will have to create its international competitiveness.Crop Production/Industries, International Relations/Trade,

The relation between post-shock temperature, cosmic-ray pressure and cosmic-ray escape for non-relativistic shocks

Supernova remnants are thought to be the dominant source of Galactic cosmic rays. This requires that at least 5% of the available energy is transferred to cosmic rays, implying a high cosmic-ray pressure downstream of supernova remnant shocks. Recently, it has been shown that the downstream temperature in some remnants is low compared to the measured shock velocities, implying that additional pressure support by accelerated particles is present. Here we use a two-fluid thermodynamic approach to derive the relation between post-shock fractional cosmic-ray pressure and post-shock temperature, assuming no additional heating beyond adiabatic heating in the shock precursor and with all non-adiabatic heating occurring at the subshock. The derived relations show that a high fractional cosmic-ray pressure is only possible, if a substantial fraction of the incoming energy flux escapes from the system. Recently a shock velocity and a downstream proton temperature were measured for a shock in the supernova remnant RCW 86. We apply the two-fluid solutions to these measurements and find that the the downstream fractional cosmic-ray pressure is at least 50% with a cosmic-ray energy flux escape of at least 20%. In general, in order to have 5% of the supernova energy go into accelerating cosmic rays, on average the post-shock cosmic-ray pressure needs to be 30% for an effective cosmic-ray adiabatic index of 4/3.Comment: 9 pages, 6 color figures. This is updated with a corrected figure 5a and 5b, reflecting an ApJ erratu

Fluids with quenched disorder: Scaling of the free energy barrier near critical points

In the context of Monte Carlo simulations, the analysis of the probability distribution $P_L(m)$ of the order parameter $m$, as obtained in simulation boxes of finite linear extension $L$, allows for an easy estimation of the location of the critical point and the critical exponents. For Ising-like systems without quenched disorder, $P_L(m)$ becomes scale invariant at the critical point, where it assumes a characteristic bimodal shape featuring two overlapping peaks. In particular, the ratio between the value of $P_L(m)$ at the peaks ($P_{L, max}$) and the value at the minimum in-between ($P_{L, min}$) becomes $L$-independent at criticality. However, for Ising-like systems with quenched random fields, we argue that instead $\Delta F_L := \ln (P_{L, max} / P_{L, min}) \propto L^\theta$ should be observed, where $\theta>0$ is the "violation of hyperscaling" exponent. Since $\theta$ is substantially non-zero, the scaling of $\Delta F_L$ with system size should be easily detectable in simulations. For two fluid models with quenched disorder, $\Delta F_L$ versus $L$ was measured, and the expected scaling was confirmed. This provides further evidence that fluids with quenched disorder belong to the universality class of the random-field Ising model.Comment: sent to J. Phys. Cond. Mat

Predictions for mass-loss rates and terminal wind velocities of massive O-type stars

Mass loss forms an important aspect of the evolution of massive stars, as well as for the enrichment of the surrounding ISM. Our goal is to predict accurate mass-loss rates and terminal wind velocities. These quantities can be compared to empirical values, thereby testing radiation-driven wind models. One specific issue is that of the "weak-wind problem", where empirically derived mass-loss rates fall orders of magnitude short of predicted values. We employ an established Monte Carlo model and a recently suggested new line acceleration formalism to solve the wind dynamics consistently. We provide a new grid of mass-loss rates and terminal wind velocities of O stars, and compare the values to empirical results. Our models fail to provide mass-loss rates for main-sequence stars below a luminosity of log(L/Lsun) = 5.2, where we run into a fundamental limit. At luminosities below this critical value there is insufficient momentum transferred in the region below the sonic point to kick-start the acceleration. This problem occurs at the location of the onset of the weak-wind problem. For O dwarfs, the boundary between being able to start a wind, and failing to do so, is at spectral type O6/O6.5. The direct cause of this failure is a combination of the lower luminosity and a lack of Fe V lines at the wind base. This might indicate that another mechanism is required to provide the necessary driving to initiate the wind. For stars more luminous than log(L/Lsun) = 5.2, our new mass-loss rates are in excellent agreement with the mass-loss prescription by Vink et al. 2000. This implies that the main assumption entering the method of the Vink et al. prescriptions - i.e. that the momentum equation is not explicitly solved for - does not compromise the reliability of the Vink et al. results for this part of parameter space (Abridged).Comment: 10 pages, 10 figures, Astronomy & Astrophysics (in press