Reliability and Delay Distributions of Train Connections

Finding reliable train connections is a considerable issue in timetable information since train delays perturb the timetable daily. We present an effective probabilistic approach for estimating the reliability of connections in a large train network. Experiments on real customer queries and real timetables for all trains in Germany show that our approach can be implemented to deliver good results at the expense of only little processing time. Based on probability distributions for train events in connections, we estimate the reliability of connections. We have analyzed our computed reliability ratings by validating our predictions against real delay data from German Railways. This study shows that we are able to predict the feasibility of connections very well. In essence, our predictions are slightly optimistic for connections with a high rating and pretty accurate for connections with a medium rating. Only for the rare cases of a very low rating, we are too pessimistic. Our probabilistic approach already delivers good results, still has improvement potential, and offers a new perspective in the search for more reliable connections in order to bring passengers safely to their destinations even in case of delays

Path Finding Strategies in Stochastic Networks *

Abstract We introduce a novel generic algorithmic problem in directed acyclic graphs, motivated by our train delay research. Roughly speaking, an arc is admissible or not subject to the value of a random variable at its tail node. The core problem is to precompute data such that a walk along admissible arcs will lead to one of the target nodes with a high probability. In the motivating application scenario, this means to meet an appointment with a high chance even if train connections are broken due to train delays. We present an efficient dynamic-programming algorithm for the generic case. The algorithm allows us to maximize the probability of success or, alternatively, optimize other criteria subject to a guaranteed probability of success. Moreover, we customize this algorithm to the application scenario. For this scenario, we present computational results based on real data from the national German railway company. The results demonstrate that our approach is superior to the natural approach, that is, to find a fast and convenient connection and to identify alternative routes for all tight train changes where the probability that the change breaks due to delays is not negligible

Understanding alliance evolution and termination: Adjustment costs and the economics of resource value

Alliances have been studied extensively in the past and various arguments have been suggested to explain their evolution and eventual termination. We argue that one important explanation of alliance termination has remained overlooked, one where the mechanism revolves around resource value and is independent of any mismanagement, opportunism, lack of trust, interpretive misunderstanding, or perceptions of inequity. In this explanation, we recognize explicitly that resources undergo transformation through an alliance, and this transformation reveals new previously imperfectly predicted costs to remain in the alliance as well as new opportunities outside the alliance. We apply the concepts of direct and indirect adjustment costs and inter-temporal economies of scope to explain these phenomena and demonstrate that, depending on the particular structure of incentive asymmetry between the two firms after alliance formation, the new circumstances may motivate a revised cost/profit sharing arrangement, a change in ownership of alliance resources, or a complete dissolution of the alliance. Some determinants of adjustment costs are explored in detail, covering resource characteristics, resource combination characteristics, and environment characteristics. Based on the economics of resource value, our argument has implications not just for alliance evolution and termination but also provides a distinct lens to explain the evolution of firm boundaries and the manner of transition of alliances into acquisitions

HIV Knowledge, Attitudes, and Practices of Young People in Iran: Findings of a National Population-Based Survey in 2013

INTRODUCTION:The evidence is mixed on the HIV knowledge, attitude, and practices of youth in Iran. The aim of the current study was to assess knowledge, attitudes, and practices of Iranian youth towards HIV through a national survey. MATERIALS AND METHODS:Through a cross-sectional study with multistage cluster sampling, we administered a pilot-tested standard questionnaire to assess the levels of HIV knowledge, attitudes and practices of individuals aged 15-29 years old. Participants were recruited from 13 provinces in Iran and consisted of 2456 men and 2412 women. RESULTS:Only 37.3% of the participants had a high knowledge score. Most participants knew the main routes of HIV transmission; however, misconceptions existed about the transmission of HIV through mosquito bites across all age groups (31.7% correct response). Positive levels of attitude wereobserved among 20.7% of the participants. Most participants believed that people living with HIV (PLHIV) should be supported (88.3%) while only 46.3% were ready to share a table with them. Among those aged 19-29 years old, the main source of HIV information was mass media (69.1%), only 13.1% had ever tested for HIV, around 20.8% had ever had extramarital sex (31.7% male vs. 9.6% female),1.8% ever injected drugs (2.9% male vs. and 0.7% female). Among sexually active subjects in this age group, only 21.8% (26.1% male vs. 7.1% female) were consistent condom users. CONCLUSIONS:The findings showed that Iranian youth and young adults have relatively insufficient overall knowledge and negative attitudes about HIV and PLHIV. Novel strategies involving schools and youth's networks could be employed to deliver a culturally sensitive sexual health program