Algebraic Connectivity and Degree Sequences of Trees

We investigate the structure of trees that have minimal algebraic connectivity among all trees with a given degree sequence. We show that such trees are caterpillars and that the vertex degrees are non-decreasing on every path on non-pendant vertices starting at the characteristic set of the Fiedler vector.Comment: 8 page

From here to infinity - sparse finite versus Dirichlet process mixtures in model-based clustering

In model-based-clustering mixture models are used to group data points into clusters. A useful concept introduced for Gaussian mixtures by Malsiner Walli et al (2016) are sparse finite mixtures, where the prior distribution on the weight distribution of a mixture with $K$ components is chosen in such a way that a priori the number of clusters in the data is random and is allowed to be smaller than $K$ with high probability. The number of cluster is then inferred a posteriori from the data. The present paper makes the following contributions in the context of sparse finite mixture modelling. First, it is illustrated that the concept of sparse finite mixture is very generic and easily extended to cluster various types of non-Gaussian data, in particular discrete data and continuous multivariate data arising from non-Gaussian clusters. Second, sparse finite mixtures are compared to Dirichlet process mixtures with respect to their ability to identify the number of clusters. For both model classes, a random hyper prior is considered for the parameters determining the weight distribution. By suitable matching of these priors, it is shown that the choice of this hyper prior is far more influential on the cluster solution than whether a sparse finite mixture or a Dirichlet process mixture is taken into consideration.Comment: Accepted versio

A Note on Queueing Systems Exposed to Disasters

We discuss queueing systems subject to total disasters. If the time intervals between successive disasters are i.i.d. random variables independent of arrival and service process and arrivals form a Poisson process, then the transient and the asymptotic analysis of such models may be based on Feller's Second Renewal Theorem. Several examples are given: the limiting behavior of M/G/1 in case of exponential disasters and its special cases M/M/1, M/M/1/K and M/M/infinity. (author´s abstract)Series: Research Report Series / Department of Statistics and Mathematic

The Investment Effects of Price Caps under Imperfect Competition. A Note.

This note analyzes a simple Cournot model where firms choose outputs and capacities facing varying demand and price-cap regulation. We find that binding price caps set above long-run marginal cost increase (rather than decrease) aggregate capacity investment. (author's abstract)Series: Working Papers / Research Institute for Regulatory Economic

Housing Rent Dynamics and Rent Regulation in St. Petersburg (1880-1917)

This article studies the evolution of housing rents in St. Petersburg between 1880 and 1917 covering an eventful period of Russian and world history. We collect and digitize over 5,000 rental advertisements from historic newspapers, which we use together with geo-coded addresses and detailed structural characteristics to construct a quality-adjusted rent price index in continuous time. We provide the first pre-war and pre-Soviet index based on market data for any Russian housing market. In 1915, one of the world's earliest rent control and tenant protection policies was introduced as a response to soaring prices following the outbreak of World War I. We analyze the impact of this policy: while before the regulation rents were increasing at a similar rapid pace as other consumer prices, the policy reversed this trend. We find evidence for official compliance with the policy, document a rise in tenure duration and strongly increased rent affordability among workers after the introduction of the policy. We conclude that the immediate prelude to the October Revolution was indeed characterized by economic turmoil, but rent affordability and rising rents were no longer the prevailing problems.Series: Department of Economics Working Paper Serie

Supporting Pluralism by Artificial Intelligence: Conceptualizing Epistemic Disagreements as Digital Artifacts

A crucial concept in philosophy and social sciences, epistemic disagreement, has not yet been adequately reflected in the Web. In this paper, we call for development of intelligent tools dealing with epistemic disagreements on the Web to support pluralism. As a first step, we present Polyphony, an ontology for representing and annotating epistemic disagreements

A paper waste prediction model

The aim of this paper is to develop a model predicting the collected amount of waste paper at the regional level of municipalities. Leaming about the factors that influence the amount of collected paper is a prerequisite for the evaluation and reorganization of collection systems. We hypothesize that the amount of collected paper depends on both, the waste potential and factors which influence the convenience such as the density of collection sites. For this study, we use a sample of 649 municipalities. The data show a high variance in terms of the collected waste paper per person and year between the municipalities. We develop a multivariate regression model providing valuable insights about the relationship between demographic parameters and the amount of collected waste paper. Furthermore, in this novel approach we found a significant positive impact of the convenience of the collection system

The Community Structure of R&D Cooperation in Europe. Evidence from a social network perspective

The focus of this paper is on pre-competitive R&D cooperation across Europe, as captured by R&D joint ventures funded by the European Commission in the time period 1998-2002, within the 5th Framework Program. The cooperations in this Framework Program give rise to a bipartite network with 72,745 network edges between 25,839 actors (representing organizations that include firms, universities, research organizations and public agencies) and 9,490 R&D projects. With this construction, participating actors are linked only through joint projects. In this paper we describe the community identification problem based on the concept of modularity, and use the recently introduced label-propagation algorithm to identify communities in the network, and differentiate the identified communities by developing community-specific profiles using social network analysis and geographic visualization techniques. We expect the results to enrich our picture of the European Research Area by providing new insights into the global and local structures of R&D cooperation across Europe

Industrial cluster formation in European regions. U.S. cluster templates and Austrian evidence.

The paper will be organized in the following manner. We first provide a concise review of how industrial trade clusters were developed from available I/O coefficients (see box), including how regional industrial data may be embedded within their "templates". Second, we will review the steps taken, using available industrial concordances, that permit regional data from other advanced national industrial systems to be embedded within these templates. Third, we will illustrate the results of applying the U.S. template for the motor vehicle industrial trade cluster to regions in both Austria and North Carolina over 5-10 year time periods. Finally, we will offer some speculative observations about what the results may indicate about regional cluster development in these two regions. (authors' abstract, ed. M.Putz)Series: SRE - Discussion Paper

Measuring the degree of virtualization. An empirical analysis in two Austrian industries.

Strategic management literature suggests that especially in young and dynamic industries Virtual Corporations are more likely to emerge, as this type of organization is flexible enough to deal with rapidly changing environments. This paper challenges the proposition that environ-mental uncertainty and technological change lead to organizational adaptation towards virtual structures. We analyzed companies of two Austrian industries, data processing and engineering, which are characterized by different rates of innovation and environmental uncertainty, and compare their strategic, structural, and process characteristics by measuring their Degree of Virtualization. Results indicate almost no difference in the Degree of Virtualization. From these findings, we draw implications for the theoretical concept of Virtual Corpora-tions as well as for empirical research. (author's abstract)Series: Report Series SFB "Adaptive Information Systems and Modelling in Economics and Management Science