7,638 research outputs found

    A Lead Market Approach Towards the Emergence and Diffusion of Coal-fired Power Plant Technology

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    Today, more than 70% of the world?s total electricity production is supplied by power plants using conventional fossil fuels. Coal accounts for more than half of the fossil fuel combustion in electricity plants. Future mega trends give reason to believe that electricity demand will double until 2030. The abundance of coal reserves in many countries and increasing fuel prices for gas and oil against the background of a growing need to provide sufficient, secure and affordable energy make coal an attractive option in worldwide electricity production. Against this background, the aim of this paper is to analyse why clean coal technologies in some countries diffuse faster and to a greater extent than in other nations. The paper applies the lead market concept. Lead markets are markets that adopt an innovation before it is adopted by most other countries and therefore lead the global diffusion of the innovation. The most important technological trajectory for coal power plants is the pulverised coal-fired steam cycle (PC) which is the basis for all other coal combustion technologies. Modern PC technology is well developed and accounts for over 90% of coal-fired capacity worldwide. Therefore it will be taken as a reference technology, with SC (Supercritical) coal-fired power generation technologies being selected as an innovative technology within this trajectory. As for the diffusion of SC, the paper concentrates on Germany, USA, China and Japan. The analysis shows that the typical lead market pattern applies only to a limited extent. In the 1960s and 1970s, the USA has established a lead market for SC technology. In the meanwhile, Japan has surpassed the United States, although it started out as typical lag market. After analysing the technology diffusion in the four countries, one central question evolves: Can we determine a lead market for coal-fired power plant technology today? The discussion of lead market factors shows that currently no clear lead market exists for coal-fired power plant technology. Although the United States still has comparative advantages in terms of prices, demand and market structure, Japan has caught up in terms of transfer advantage and Germany in terms of regulation. In the near future, demand advantages will switch to China. This supports also the hypothesis that - apart from the demand-oriented lead market model - push factors such as R&D activity play a strong role as well. The transfer advantage of Japan stems mainly from its intensive R&D activities. Thus it can be concluded that a mix of push and pull policies is necessary in order to establish a lead market position. --Lead Markets,Coal Power plants,Energy Technology,Energy Policy

    How the First Stars Regulated Local Star Formation I: Radiative Feedback

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    We present numerical simulations of how a 120 M_\odot primordial star regulates star formation in nearby cosmological halos at zz \sim 20 by photoevaporation. Our models include nine-species primordial chemistry and self-consistent multifrequency conservative transfer of UV photons with all relevant radiative processes. Whether or not new stars form in halos clustered around a Population III star ultimately depends on their core densities and proximity to the star. Diffuse halos with central densities below 2 - 3 cm3^{-3} are completely ionized and evaporated anywhere in the cluster. Evolved halos with core densities above 2000 cm3^{-3} are impervious to both ionizing and Lyman-Werner flux at most distances from the star and collapse as quickly as they would in its absence. Star formation in halos of intermediate density can be either promoted or suppressed depending on how the I-front remnant shock compresses, deforms and enriches the core with H2_2. We find that the 120 M_\odot star photodissociates H2_2 in most halos in the cluster but that catalysis by H- restores it a few hundred kyr after the death of the star, with little effect on star formation. Our models exhibit significant departures from previous one-dimensional spherically-symmetric simulations, which are prone to serious errors due to unphysical geometric focusing effects.Comment: 20 pages, 19 figures, accepted by ApJ, title and abstract change

    Photoionization of Clustered Halos by the First Stars

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    We present numerical simulations of the photoevaporation of cosmological halos clustered around a 120 M_\odot primordial star, confining our study to structures capable of hosting Population III star formation. The calculations include self-consistent multifrequency conservative transfer of UV photons together with nine-species primordial chemistry and all relevant radiative processes. The ultimate fates of these halos varies with central density and proximity to the central source but generally fall into one of four categories. Diffuse halos with central densities below 2 - 3 cm3^{-3} are completely ionized and evaporated by the central star anywhere in the cluster. More evolved halo cores at densities above 2000 cm3^{-3} are impervious to both ionizing and Lyman-Werner flux at most distances from the star and collapse of their cores proceeds without delay. Radiative feedback in halos of intermediate density can be either positive or negative, depending on how the I-front remnant shock both compresses and deforms the core and enriches it with H2_2. We find that the 120 M_\odot star photodissociates H2_2 in most halos within the cluster but that catalysis by H- rapidly restores molecular hydrogen within a few hundred Kyr after the death of the star, with little delay in star formation. Our models exhibit significant departures from previous one-dimensional spherically-symmetric simulations, which are prone to serious errors due to unphysical geometric focusing effects.Comment: 5 pages, 5 figures, to appear in "First Stars III", eds. B. O'Shea, A. Heger and T. Abe

    #CotedIvoire: Why the 2015 Presidential Election was Peaceful

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    Hannah Smidt examines the factors that led to breaking the cycle of violence in the 2015 Côte d’Ivoire elections
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