The Performance of German Water Utilities: A (Semi)-Parametric Analysis

Germany's water supply industry is characterized by a multitude of utilities and widely diverging prices, possibly resulting from structural differences beyond the control of firms' management, but also from inefficiencies. In this article we use Data Envelopment Analysis and Stochastic Frontier Analysis to determine the utilities' technical efficiency scores based on cross-sectional data from 373 public and private water utilities in 2006. We find large differences in technical efficiency scores even after accounting for significant structural variables like network density, share of groundwater usage and water losses.Water supply, technical efficiency, data envelopment analysis, stochastic frontier analysis, structural variables, bootstrapped truncated regression

Potential Gains from Mergers in Local Public Transport: An Efficiency Analysis Applied to Germany

We analyze potential gains from hypothetical mergers in local public transport using the non-parametric Data Envelopment Analysis with bias corrections by means of bootstrapping. Our sample consists of 41 public transport companies from Germany's most densely populated region, North Rhine-Westphalia. We merge them into geographically meaningful, larger units that operate partially on a joint tram network. Merger gains are then decomposed into individual technical efficiency, synergy and size effects following the methodology of Bogetoft and Wang [Bogetoft, P., Wang, D., 2005. Estimating the Potential Gains from Mergers. Journal of Productivity Analysis, 23(2), 145-171]. Our empirical findings suggest that substantial gains up to 16 percent of factor inputs are present, mainly resulting from synergy effects.Merger, Public Transport, Efficiency, Data Envelopment Analysis

Migration reversal of soft particles in vertical flows

Non-neutrally buoyant soft particles in vertical microflows are investigated. We find, soft particles lighter than the liquid migrate to off-center streamlines in a downward Poiseuille flow (buoyancy-force antiparallel to flow). In contrast, heavy soft particles migrate to the center of the downward (and vanishing) Poiseuille flow. A reversal of the flow direction causes in both cases a reversal of the migration direction, i. e. heavier (lighter) particles migrate away from (to) the center of a parabolic flow profile. Non-neutrally buoyant particles migrate also in a linear shear flow across the parallel streamlines: heavy (light) particles migrate along (antiparallel to) the local shear gradient. This surprising, flow-dependent migration is characterized by simulations and analytical calculations for small particle deformations, confirming our plausible explanation of the effect. This density dependent migration reversal may be useful for separating particles.Comment: 8 pages, 7 figure

Eigenvalue Distributions of Reduced Density Matrices

Given a random quantum state of multiple distinguishable or indistinguishable particles, we provide an effective method, rooted in symplectic geometry, to compute the joint probability distribution of the eigenvalues of its one-body reduced density matrices. As a corollary, by taking the distribution's support, which is a convex moment polytope, we recover a complete solution to the one-body quantum marginal problem. We obtain the probability distribution by reducing to the corresponding distribution of diagonal entries (i.e., to the quantitative version of a classical marginal problem), which is then determined algorithmically. This reduction applies more generally to symplectic geometry, relating invariant measures for the coadjoint action of a compact Lie group to their projections onto a Cartan subalgebra, and can also be quantized to provide an efficient algorithm for computing bounded height Kronecker and plethysm coefficients.Comment: 51 pages, 7 figure

Quantization of gauge fields, graph polynomials and graph cohomology

We review quantization of gauge fields using algebraic properties of 3-regular graphs. We derive the Feynman integrand at n loops for a non-abelian gauge theory quantized in a covariant gauge from scalar integrands for connected 3-regular graphs, obtained from the two Symanzik polynomials. The transition to the full gauge theory amplitude is obtained by the use of a third, new, graph polynomial, the corolla polynomial. This implies effectively a covariant quantization without ghosts, where all the relevant signs of the ghost sector are incorporated in a double complex furnished by the corolla polynomial -we call it cycle homology- and by graph homology.Comment: 44p, many figures, to appea