In: Journal of Discrete Algorithms, 2012, vol. 17, p. 95-102
Let G = (V , E) be a graph in which every vertex v ∈ V has a weight w(v)>=0 and a cost c(v) >=0. Let SG be the family of all maximum-weight stable sets in G. For any integer d 0, a minimum d-transversal in the graph G with respect to SG is a subset of vertices T ⊆ V of minimum total cost such that |T ∩ S| d for every S ∈ SG. In this paper, we present a polynomial-time algorithm to...
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In: Health economics, 2011, vol. 20, no. 4, p. 484-504
Using exceptionally rich linked administrative and survey information on German welfare recipients we investigate the health effects of transitions from welfare to employment and of assignments to welfare-to-work programmes. Applying semi- parametric propensity score matching estimators we find that employment substantially increases (mental) health. The positive effects are mainly driven by...
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In: Journal of Applied Econometrics, 2014, vol. 29, no. 6, p. 920-943
This paper demonstrates the identification of causal mechanisms of a binary treatment under selection on observables, (primarily) based on inverse probability weighting; i.e. we consider the average indirect effect of the treatment, which operates through an intermediate variable (or mediator) that is situated on the causal path between the treatment and the outcome, as well as the...
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In: Journal of Applied Econometrics, 2015, vol. 30, no. 7, p. 1144-1168
Identification in most sample selection models depends on the independence of the regressors and the error terms conditional on the selection probability. All quantile and mean functions are parallel in these models; this implies that quantile estimators cannot reveal any—per assumption non-existing—heterogeneity. Quantile estimators are nevertheless useful for testing the conditional...
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In: Studies in Communication Sciences, 2013, vol. 13, no. 2, p. 139-147
tWith the rise of Web 2.0 the discussion about professional journalism changing radically or even becom-ing obsolete in the future has intensified. Up to now, empirical findings mainly stem from research on(micro-)blogging and show its complementary rather than equivalent function compared with profes-sional journalism. Amazingly, the performance of collaborative amateur news websites with an...
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In: Einführung in die Archäometrie, 2007, p. 237-259
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In: The European Physical Journal B, 2008, vol. 66, no. 4, p. 557-561
Keywords in scientific articles have found their significance in information filtering and classification. In this article, we empirically investigated statistical characteristics and evolutionary properties of keywords in a very famous journal, namely Proceedings of the National Academy of Science of the United States of America (PNAS), including frequency distribution, temporal scaling...
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In: The European Physical Journal B, 2008, vol. 63, no. 2, p. 273-278
We investigate a network model based on an infinite regular square lattice embedded in the Euclidean plane where the node connection probability is given by the geometrical distance of nodes. We show that the degree distribution in the basic model is sharply peaked around its mean value. Since the model was originally developed to mimic the social network of acquaintances, to broaden the degree...
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In: The European Physical Journal B, 2008, vol. 62, no. 1, p. 101-104
We propose a novel capacity model for complex networks against cascading failure. In this model, vertices with both higher loads and larger degrees should be paid more extra capacities, i.e. the allocation of extra capacity on vertex i will be proportional to ki γ , where ki is the degree of vertex i and γ > 0 is a free parameter. We have applied this model...
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In: Journal of Econometrics, 2006, vol. 133, no. 1, p. 153-190
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