What Drives the Efficiency of Hard Coal Fuelled Electricity Generation? An Empirical Assessment

The efficiency of electricity generation in hard coal fired power plants varies considerably from country to country and over time. These differences occur both between developing and developed countries and between industrialised nations. The econometric analysis presented in this paper tests for the reasons of these discrepancies. In this examination abundance of hard coal and the price of hard coal are the two variables of our major interest. We assume that countries with an abundance of hard coal or relatively low costs of extraction show smaller degrees of efficiency than countries with poor deposits of this resource because the latter nations have a stronger dependency on efficient power plants than the former. Furthermore, higher prices should lead to more efficient electricity generation since production costs increase with growing hard coal prices. Our findings partially confirm these hypotheses and suggest that, among the chosen explanatory variables, hard coal abundance or the accessibility of hard coal, respectively, the hard coal price, the level of foreign direct investment inflows as well as the average power plant age are identified as principal drivers of power plant efficiency. From an environmental policy perspective we conclude that flexible policy instruments which internalise external effects caused by emissions as well as support for foreign investments are important means to foster energy efficiency. However, economic efficiency even if contrasting with energy efficiency must not be neglected in the design of energy policies. --energy efficiency,natural resources,hard coal fired power plant

A discrete version of the Darboux transform for isothermic surfaces

We study Christoffel and Darboux transforms of discrete isothermic nets in 4-dimensional Euclidean space: definitions and basic properties are derived. Analogies with the smooth case are discussed and a definition for discrete Ribaucour congruences is given. Surfaces of constant mean curvature are special among all isothermic surfaces: they can be characterized by the fact that their parallel constant mean curvature surfaces are Christoffel and Darboux transforms at the same time. This characterization is used to define discrete nets of constant mean curvature. Basic properties of discrete nets of constant mean curvature are derived.Comment: 30 pages, LaTeX, a version with high quality figures is available at http://www-sfb288.math.tu-berlin.de/preprints.htm

The cost of phasing out nuclear power: a quantitative assessment of alternative scenarios for Germany

In the debate on the premature phase-out of nuclear power generation in Germany, there is an intense dispute on the effective operating time for the existing nuclear power plants. This paper addresses the question of how alternative phase-out regulations affect both the magnitude of total economic costs and the distribution of these costs across nuclear power plants and competing companies. Based on a dynamic partial equilibrium analysis of power supply options, we quantify the excess costs of different regulatory approaches as a function over time and investigate the implied competitive effects at the plant as well as at the company level. We find that alternative phase-out regulations which effectively lead to the same date for an ultimate shutdown of nuclear power generation exhibit large differences in total costs. The competitive distortions across companies also vary considerably with the chosen regulation depending on how the respective cost implications at the plant level get distributed at the company level via the specific ownership. Our quantitative results refer to nuclear phase-out scenarios for Germany and its specific plant structure as well as plant-ownership by companies. However, the issues and methodological approaches presented in this paper may be important for other industrialized countries which also contemplate a premature nuclear phase-out. --

Minimal surfaces from circle patterns: Geometry from combinatorics

We suggest a new definition for discrete minimal surfaces in terms of sphere packings with orthogonally intersecting circles. These discrete minimal surfaces can be constructed from Schramm's circle patterns. We present a variational principle which allows us to construct discrete analogues of some classical minimal surfaces. The data used for the construction are purely combinatorial--the combinatorics of the curvature line pattern. A Weierstrass-type representation and an associated family are derived. We show the convergence to continuous minimal surfaces.Comment: 30 pages, many figures, some in reduced resolution. v2: Extended introduction. Minor changes in presentation. v3: revision according to the referee's suggestions, improved & expanded exposition, references added, minor mistakes correcte