Relations Between Graphs

Given two graphs G and H, we ask under which conditions there is a relation R that generates the edges of H given the structure of graph G. This construction can be seen as a form of multihomomorphism. It generalizes surjective homomorphisms of graphs and naturally leads to notions of R-retractions, R-cores, and R-cocores of graphs. Both R-cores and R-cocores of graphs are unique up to isomorphism and can be computed in polynomial time.Comment: accepted by Ars Mathematica Contemporane

Explaining interviewer effects and respondent behavior: Theoretical models and empirical analysis

Reinecke J, Schmidt P. Explaining interviewer effects and respondent behavior: Theoretical models and empirical analysis. Quality and Quantity. 1993;27(3):219-247.The behavior of respondents in interview situations has been dealt on the one hand with respect to many empirical studies and on the other hand in connection with different theoretical approaches (Hyman 1954; Cannell & Kahn 1968). In this paper the most relevant theoretical explanations are discussed and systematized from the point of view of the theory of reasoned action (Ajzen & Fishbein 1980). Whereas this theory program has been used in many substantive fields, it has rarely been applied to the problem of interviewer effects and response sets. In this approach one assumes that the actors in interview situations decide according to cost-benefit calculations. The theory of reasoned action is viewed as an operationalized theory, discussed in more detail and formalized via structural equation models. These models are empirically tested with the data of a survey specifically designed to perform such a method study. The reported contact rates of German with foreigners is the dependent variable under study. First, a model without interviewer variables is tested to explain respondent behavior in terms of norms, attitudes and some other determinants. Then the status and the age of interviewers are introduced as situational determinants of the respondents' behavior. For subgroup analyses the respondents are divided into three groups varying in the amount of the need for social approval. The models are tested according to two subgroups (low and high need for social approval) with the technique of multiple group comparison in LISREL (Jöreskog/Sörbom 1988). All models and results are interpreted in terms of the theory of reasoned action. At the end some conclusions for modelling interviewer effects and respondent behavior are discussed

Numerical simulation of growth of Escherichia coli in unsaturated porous media

A model for the aerobic and anaerobic growth of Escherichia coli (HB101 K12 pGLO) depending on the concentration of oxygen and DOC as substrate has been developed based on laboratory batch experiments. Using inverse modelling to obtain optimal sets of parameters, it could be shown that a model based on a modified double Contois kinetic can predict cell densities, organic carbon utilisation, oxygen transfer and utilisation rates for a large number of experiments under aerobic and anaerobic conditions with a single unique set of parameters. The model was extended to describe growth of E. coli in unsaturated porous media, combining diffusion, phase exchange and microbiological growth. Experiments in a Hele-Shaw cell, filled with quartz sand, were conducted to study bacterial growth in the capillary fringe above a saturated porous medium. Cell density profiles in the Hele-Shaw cell were predicted with the growth model and the parameters from the batch experiments without any further calibration. They showed a very good qualitative and quantitative agreement with cell densities determined from samples taken from the Hele-Shaw cell by re-suspension and subsequent counting. Thus it could be shown, that it is possible to successfully transfer growth parameters from batch experiments to porous media for both aerobic and anaerobic conditions.Comment: Minor changes in conclusions, results unchange

Deutsche Direktinvestitionen in Entwicklungs- und Reformländern : haben sich die Motive gewandelt?.

Direktinvestition; Deutsch; Standortfaktor; Schätzung; Deutschland; Entwicklungsländer; Osteuropa;

Multiphysics Simulation of a Battery Electric Train Operation

The changeover from diesel driven multiple units to battery electric multiple units is a challenge for operators due to the limited range of these trains. Therefore, in this paper a tool is developed and described that simulates the entire operation of a battery electric train. The tool contains a model of the track, the vehicle, the timetable and the environment. The model of the track is built on elevation profiles, radius information and speed limitation. The vehicle model is derived from an electric multiple unit suitable for local and commuter train operation. To do parametric studies or model different train units it is easily possible to change vehicle properties. Modeling the timetable and the environment allows the simulation of an entire operation day. The overall simulation model was validated and is consistent. Finally examples show the simulation possibilities and features of the tool