Optimization problems with color-induced budget constraints

In 1984, Gabow and Tarjan provided a very elegant and fast algorithm for the following problem: given a matroid defined on a red and blue colored ground set, determine a basis of minimum cost among those with k red elements, or decide that no such basis exists. In this paper, we investigate extensions of this problem from ordinary matroids to the more general notion of poset matroids which take precedence constraints on the ground set into account. We show that the problem on general poset matroids becomes -hard, already if the underlying partially ordered set (poset) consists of binary trees of height two. On the positive side, we present two algorithms: a pseudopolynomial one for integer polymatroids, i.e., the case where the poset consists of disjoint chains, and a polynomial algorithm for the problem to determine a minimum cost ideal of size l with k red elements, i.e., the uniform rank-l poset matroid, on series-parallel posets.     

Coopetition in coworking-spaces: value creation and appropriation tensions in an entrepreneurial space

Coopetition has the potential to improve entrepreneurship and innovation. It will be prevalent in coworking-spaces building a growing field for individual and corporate entrepreneurship. The individuals’ physical closeness in the professional and social space of the coworking-space eases multifaceted transfers of explicit and implicit knowledge, stimulating creation, transfer, overhaul, and implementation of entrepreneurial ideas. While entrepreneurs in these coworking-spaces collaborate on sharing knowledge and resources and on finding creative ideas from which can breed new venture concepts, they simultaneously compete on the appropriation of values. Thus, entrepreneurs in coworking-spaces face coopetitive tensions of creating and appropriating the values. Based  on  interview data and secondary sources, this paper explains four different prototype institutions of coworking-spaces: the corporate coworking-space, the open corporate coworking-space, the consultancy coworking-space, and the independent coworking-space. Study explains different tensions of value creation and appropriation that occur within the coopetition in the different forms of coworking-spaces.     

Contract design and insurance fraud: an experimental investigation

This paper experimentally examines the impact of contract design on insurance fraud. We test how fraud behavior varies for insurance contracts with full coverage, a straight deductible or claim-dependent premiums (bonus-malus contracts), in a setup where rational and selfish individuals have an incentive to always claim the maximum possible indemnity. We find a substantial impact of contractual arrangements: Deductible contracts lead to a greater extent to claim build-up than full coverage contracts. In contrast, bonus-malus contracts that entail the same net gains from fraud as deductible contracts do not increase claim build-up. Thus, our results indicate that bonus-malus contracts may be superior to deductible contracts for behavioral reasons.     

The disenchantment of Bitcoin: unveiling the myth of a digital currency

Bitcoin and its peculiar, decentralized transaction system, have already ignited interest by professional and retail traders in search for profits and by economists and legal experts, looking for possible regulation to contain illegal uses. We instead examine the unexpected and ongoing success of Bitcoin from a sociological perspective, first questioning its unusual legitimation system, backed by the so called ‘blockchain technology’, instead of by governmental authorities. Then we collect data and elements to reconstruct Bitcoin’s history as a cryptocurrency, starting from the mysterious story surrounding its birth. We then follow its spread and development through social networks and words of mouth, together with its sudden booms and bursts, finally to suggest that both users and institutional regulators should be aware of the risks of Bitcoin and of its alleged power to challenge our very notion of money.     

Participatory Spaces of Mental Health Service User Organizations in the Post-deinstitutional Era: Mapping Roles and Challenges

By applying the concept of participatory spaces, this article maps and analyzes current research on mental health service user organizations (MHSUOs). We have analyzed research literature from 2006 to 2016 to examine how the role of and challenges facing MHSUOs are formulated in the post-deinstitutional era. The current situation is marked by MHSUOs parallel presence in invited, claimed and popular spaces for participation. The post-deinstitutional era is characterized by a shift in focus from gaining access to such participatory spaces, to critically examining the political opportunities available in these. We further argue that the dominance of psychiatry-specific spaces could prevent MHSUOs from fully exploring their potential for participation in broader social issues.     

Double ASN Minimax sampling plans by variables when the standard deviation is unknown

We deal with the double sampling plans by variables proposed by Bowker and Goode (Sampling Inspection by Variables, McGraw–Hill, New York, 1952) when the standard deviation is unknown. Using the procedure for the calculation of the OC given by Krumbholz and Rohr (Allg. Stat. Arch. 90:233–251, 2006), we present an optimization algorithm allowing to determine the ASN Minimax plan. This plan, among all double plans satisfying the classical two-point-condition on the OC, has the minimal ASN maximum.