Estimation of geodesic tortuosity and constrictivity in stationary random closed sets

We investigate the problem of estimating geodesic tortuosity and constrictivity as two structural characteristics of stationary random closed sets. They are of central importance for the analysis of effective transport properties in porous or composite materials. Loosely speaking, geodesic tortuosity measures the windedness of paths, whereas the notion of constrictivity captures the appearance of bottlenecks resulting from narrow passages within a given materials phase. We first provide mathematically precise definitions of these quantities and introduce appropriate estimators. Then, we show strong consistency of these estimators for unboundedly growing sampling windows. In order to apply our estimators to real data sets, the extent of edge effects needs to be controlled. This is illustrated using a model for a multiphase material that is incorporated in solid oxide fuel cells.     

Wearing corset,losing shape: The euro's effect on trade imbalances

When does trade become a one-way relationship? We study bilateral trade balances for a sample of 18 European countries over the period from 1948 through 2008. We find that, with the introduction of the euro, trade imbalances among euro area members widened considerably, even after allowing for permanent asymmetries in trade competitiveness within pairs of countries or in the overall trade competitiveness of individual countries. This is consistent with indications that pair-wise trade tends to be more balanced when nominal exchange rates are flexible. Intra-euro area imbalances also seem to have become more persistent with the introduction of the euro, some of which is linked to labor market inflexibility. Reviewing the direction of imbalances, we find that bilateral trade surpluses are decreasing in the real exchange rate, decreasing in growth differentials, and increasing in the relative volatility of national business cycles. Finally, countries with relatively higher fiscal deficits and less flexible labor and product markets exhibit systematically lower trade surpluses than others.     

Effectiveness of an educational intervention to increase knowledge and reduce use of risky behaviors associated with cumulative trauma in office workers

OBJECTIVE: This pilot project assessed the effectiveness of an intervention to increase knowledge and reduce risky behaviors related to cumulative trauma disorders (CTD) in office workers. STUDY DESIGN: All 124 employees from the administrative offices of a health maintenance organization were invited to participate. Subjects were followed across time using an identification number. Data were collected via questionnaire in June 1994 (pretest1) (N=84), August 1994 (pretest II) (N= 63) and September 1995 (posttest) (N=40). The yearlong intervention focused on functional activities to prevent CTD. RESULTS: of chi-square analyses for the 40 subjects who completed all surveys indicated this intervention significantly increased overall knowledge of CTD (p =.002). Significant changes in self-reported hand/wrist (p =.016) and neck/shoulder (p =.003) posture were also found. CONCLUSIONS: This study is a first step in identifying effective educational interventions to increase knowledge and reduce risk factors related to CTD in office workers.     

The Process of Vertical Dis-Integration: An Evolutionary Perspective on Outsourcing

It is argued that an evolutionaryperspective on firm boundaries with its strongfocus on knowledge, as well as processes ofsearch, learning and capability development isinstrumental in developing a theory of firmboundaries that is close to managerialconcerns. Building on insights in evolutionaryeconomics, propositions are developed regardingscope, speed, and switching costs in theprocess of vertical dis-integration of whichoutsourcing is a particular instance. Currenttheories of firm boundaries give indication whycertain activities might be candidates foroutsourcing by stressing efficiency gains interms of transaction and production costs. They overlook, however, that ``technologicallyseparable interface' between activities might notbe available in codified form, and neglectlearning dynamics that lead to strategicconsequences in terms of capability developmentand adaptability in competitive environments ofvarying dynamics. An evolutionary perspectiveon vertical dis-integration recognises thatfirms make contractual commitments and partlytacit capabilities develop in a path-dependentmanner. The fact that the firm's past casts ashadow on current governance options, andpossibilities to realise them, complicates theprocess of governance change and imposesswitching costs that impact the scope and speedof vertical dis-integration. An evolutionaryperspective on vertical dis-integration alsosuggests considering long-term consequences ofoutsourcing decisions on the dynamiccapabilities of the firm.     

Wodurch kann die soziale Ungleichheit des Schulerfolgs am stärksten verringert werden?

Social inequality of student achievement in school has a variety of causes, all of them are well investigated scientifically. But, if a particular cause could be neutralized, which of these causes would have the strongest effect of reducing social inequality? Based on data of the PISA 2000 study, the contribution argues that the secondary social effect, which mainly represents the parental decisions for transitions to different branches of the higher educational system, has at least the same quantity as the primary social effect, which consists in all family background conditions of a student. Simple simulations show how the social inequality will change, if either the primary or the secondary social effect are neutralized. These changes cannot be forecasted in an easy or linear way under different conditions.     

Sind Universitätsprüfungen objektiv?

In diesem Beitrag werden Ergebnisse aus einem quantitativ-historischen Forschungsprojekt vorgestellt, die es zulassen, die provokative Titelfrage nach der Objektivit?t von akademischen Prüfungen in der Zeit bis 1945 zu stellen. Die Objektivit?t wird dadurch in Frage gestellt, dass die Quoten des Nicht-Bestehens in universit?ren und nach-universit?ren Abschlussprüfungen systematisch im Zeitverlauf stiegen und fielen, und zwar im Rhythmus der Arbeitsmarktchancen der jeweiligen Karrieren, die mit dem Studienfach verbunden sind: In Zeiten von überfüllung in den Karrieren bestanden prozentual mehr Kandidaten die Prüfungen nicht. Ein m?glicher Grund sind ?nderungen des „Selektionsklimas“ im Bildungssystem. Dieser Zusammenhang k?nnte auch nach 1945 bis heute weiterbestanden haben, obwohl die bisher schlechte Datenlage hier keine generelle Aussage zul?sst.