Feigenbaum graphs: a complex network perspective of chaos

The recently formulated theory of horizontal visibility graphs transforms time series into graphs and allows the possibility of studying dynamical systems through the characterization of their associated networks. This method leads to a natural graph-theoretical description of nonlinear systems with qualities in the spirit of symbolic dynamics. We support our claim via the case study of the period-doubling and band-splitting attractor cascades that characterize unimodal maps. We provide a universal analytical description of this classic scenario in terms of the horizontal visibility graphs associated with the dynamics within the attractors, that we call Feigenbaum graphs, independent of map nonlinearity or other particulars. We derive exact results for their degree distribution and related quantities, recast them in the context of the renormalization group and find that its fixed points coincide with those of network entropy optimization. Furthermore, we show that the network entropy mimics the Lyapunov exponent of the map independently of its sign, hinting at a Pesin-like relation equally valid out of chaos.Comment: Published in PLoS ONE (Sep 2011

The impact of digital start-up founders’ higher education on reaching equity investment milestones

This paper builds on human capital theory to assess the importance of formal education among graduate entrepreneurs. Using a sample of 4.953 digital start-ups the paper evaluates the impact of start-up founding teams’ higher education on the probability of securing equity investment and subsequent exit for investors. The main findings are: (1), teams with a founder that has a technical education are less likely to remain self-financed and are more likely to secure equity investment and to exit, but the impact of technical education declines with higher level degrees, (2) teams with a founder that has doctoral level business education are less likely to remain self-financed and have a higher probability of securing equity investment, while undergraduate and postgraduate business education have no significant effect, and (3) teams with a founder that has an undergraduate general education (arts and humanities) are less likely to remain self-financed and are more likely to secure equity investment and exit while postgraduate and doctoral general education have no significant effect on securing equity investment and exit. The findings enhance our understanding of factors that influence digital start-ups achieving equity milestones by showing the heterogeneous influence of different types of higher education, and therefore human capital, on new ventures achieving equity milestones. The results suggest that researchers and policy-makers should extend their consideration of universities entrepreneurial activity to include the development of human capital

Yes, we can!:building a capable initial team for a software startup

Abstract Startup companies are based on the founders’ innovations and visions of new business opportunities. Software startups are commonly considered as especially innovative. Besides the importance of the innovation and business vision, in the early stages of the startup, the initial team plays a key role in transforming the innovation into a product or a service. At the same time, software startups are often small, immature companies with very limited resources. That highlights the importance of the initial team’s capabilities to address the challenges of product development from the innovation—the knowledge, experiences, skills, and other cognitive abilities. In this chapter, we present the results of studies on the initial team’s capabilities from the viewpoint of the product development, planning, designing, implementing, and verifying the targeted product or service. The studies were conducted on a group of 13 software startups in Italy, Norway, and Finland. The studies revealed that from a group of very heterogeneous software startups a generic structure of the initial team could be identified, consisting of three different roles, each having a specific set of responsibilities and capability needs. This team structure provides a software startup with a balance between the team’s capabilities and problems and challenges to be solved during the early product development process. In addition, we present the sources of the needed capabilities, the initial knowledge, experience, and skills of the founder, and broadening and deepening the initial capabilities by validated learning and by growth toward the identified team structure

Phenytoin Pharmacokinetics After Intravenous Administration to Patients Receiving Enteral Tube-Feeding

Serial plasma samples were collected after administration of 13 intravenous dose of phenytoin to 11 patients with head injury; 5 to patients who had been receiving enteral feeds for less than 5 days (group 1), and 8 to patients who had been receiving enteral feeds for loner than 5 days (group 2). Average plasma phenytoin concentrations were higher in group 1 than in group 2 (0.003). The median intravenous study dose was the same (300 mg) in both groups (p=0.17). Group 2 received slightly higher doses expressed as mg/kg (median of 5.45 mg/kg compared to 4.29 mg/kg in group 1, p=0.21). Phenytoin was more rapidly eliminated following intravenous dosing patients receiving long-term enteral feeding. V-max was higher in group 2 than in group 1 (medians, 709 versus 394 mg/day) and K-m smaller (medians, 2.5 versus 3.9 mg/l), but volume of distribution was similar in both groups (p=0.88). The kinetic parameters of phenytoin in group 1 were similar to previously published population pharmacokinetic parameters. In order to maintain phenytoin concentrations adequate for seizure prophylaxis in patients receiving long-term enteral feeding it would be advisable to decrease the dosing interval as well as increasing the phenytoin dose when the drug is administered intravenously