Search results for "Operations Research"
showing 10 items of 1297 documents
Quantifying sunk costs and learning effects in R&D persistence
2020
Abstract This paper analyzes and quantifies the fundamental factors that are likely to cause persistence in performing R&D activities: the existence of sunk costs associated with R&D activities and the process of learning that characterizes this type of activity. We estimate our model with Spanish manufacturing firms for the period 1991-2014. By decomposing the effects of sunk costs and learning effects, we find that both are important determinants of R&D persistence, and that failing to allow for learning systematically overestimates sunk cost effects. Both large firms and SMEs benefit from direct and indirect (via productivity) effects of R&D experience, but in large firms this is more li…
Child–display interaction:Lessons learned on touchless avatar-based large display interfaces
2020
AbstractDuring the last decade, touchless gestural interfaces have been widely studied as one of the most promising interaction paradigms in the context of pervasive displays. In particular, avatars and silhouettes have proved to be effective in making the touchless capacity of displays self-evident. In this paper, we focus on a child–display interaction approach to avatar-based touchless gestural interfaces. We believe that large displays offer an opportunity to stimulate children’s experiences and engagement; for instance, learning about art is very engaging for children but can bring a number of challenges. Our study aims to contribute to the literature on both pervasive displays and chi…
Strategies for Including Patients Recruited During Interim Analysis of Clinical Trials
2007
In clinical trials a periodical check of safety and efficacy data is often needed. For organizational reasons it is rarely desirable to stop a trial during such an interim analysis. Therefore, new study patients are included in the trial while the interim analysis is ongoing. Disregarding the additional information provided by these interim patients would be unsatisfactory, especially for an office of regulatory affairs. Consequently, the rules for group sequential or adaptive decisions must be adjusted to the recruitment of interim patients. In this paper, two strategies for modifying study designs to consider the analysis of interim patients are proposed.
Evolution of correlation structure of industrial indices of U.S. equity markets
2013
We investigate the dynamics of correlations present between pairs of industry indices of US stocks traded in US markets by studying correlation based networks and spectral properties of the correlation matrix. The study is performed by using 49 industry index time series computed by K. French and E. Fama during the time period from July 1969 to December 2011 that is spanning more than 40 years. We show that the correlation between industry indices presents both a fast and a slow dynamics. The slow dynamics has a time scale longer than five years showing that a different degree of diversification of the investment is possible in different periods of time. On top to this slow dynamics, we als…
Search for excited leptons in Z0 decay
1990
Due to the severity of system-wide power outages, though their probability of occurrence is slight, regulatory authorities require that a system restoration plan be drawn up and kept up to date at all times. The power outage that affected northeastern North America in 2003 proved the need for such a requirement. The particular structure of Hydro-Quebec's power system requires the use of a highly specific system restoration procedure. The daily preparation of the system restoration plan is based on a strategy whose application requires that a restoration sequence be drawn up that uses available equipment, the electrical behavior of which has been validated using appropriate studies. Over the…
Models and solution methods for the uncapacitatedr-allocationp-hub equitable center problem
2017
Hub networks are commonly used in telecommunications and logistics to connect origins to destinations in situations where a direct connection between each origin–destination (o-d) pair is impractical or too costly. Hubs serve as switching points to consolidate and route traffic in order to realize economies of scale. The main decisions associated with hub-network problems include (1) determining the number of hubs (p), (2) selecting the p-nodes in the network that will serve as hubs, (3) allocating non-hub nodes (terminals) to up to r-hubs, and (4) routing the pairwise o-d traffic. Typically, hub location problems include all four decisions while hub allocation problems assume that the valu…
On the hardness of evaluating criticality of activities in a planar network with duration intervals
2003
Complexity results for problems of evaluating the criticality of activities in planar networks with duration time intervals are presented. We show that the problems of asserting whether an activity is possibly critical, and of computing bounds on the float of an activity in these networks are NP-complete and NP-hard, respectively.
Persecution and Patronage: Oscar Buneman’s years in Britain
2016
The German student Oscar Bunemann, in trouble with the Nazi authorities in the mid-1930s, chose to emigrate to Britain and pursue a PhD there. After emigration, his surname appears as Buneman. On the verge of completing his degree in 1940, he was detained as an enemy alien and spent almost a year in internment. Upon release, he found work as an atomic scientist in England, and went on to lead a post-war career as a pioneering plasma physicist in the USA.We study forced migration of European scientists before and during the Second World War, and scientific patronage in the host countries. Buneman’s case is interesting from several points of view. Being a non-Jewish, non-communist, anti-Nazi …
A new indicator for higher education student performance
2014
The debate on academic achievement is a heated issue that involves all the higher education contexts. This paper attempts to provide an indicator that can make the measurement of university student performance easier and that can be easily applied to different systems, making comparisons more fair. The Italian University System is used as a starting point to make several considerations on the current measures and to build up a new performance indicator. Then, a generalization for other marking systems is shown and finally a quantile regression is performed to investigate some determinants of the new performance indicator, also with respect to the current one.
The Olt River pollution monitoring, using spatial analysis, analityc hierarchy process and technique for order preference by similarity methods
2016
Abstract Environmental pollution is one of the most serious problems of the contemporary world. Chemical industry is one of the major sources of environmental pollutants. Human knowledge and experience is currently focused on the use of assessment methods and techniques before and during the onset of such activities. For instance, it is common to consider the integration of multiple constraining factors and also, taking into account their high complexity and the application of one of the various techniques of Multi-Criteria Decision Making. The purpose of this study is to determine the location of the least and most polluted areas from several sampling points on the Olt River, in Romania. I…