Network Position (network + position)

Distribution by Scientific Domains


Selected Abstracts


A NEGATIVE RELATIONSHIP BETWEEN MUTATION PLEIOTROPY AND FITNESS EFFECT IN YEAST

EVOLUTION, Issue 6 2007
Tim F. Cooper
It is generally thought that random mutations will, on average, reduce an organism's fitness because resulting phenotypic changes are likely to be maladaptive. This relationship leads to the prediction that mutations that alter more phenotypic traits, that is, are more pleiotropic, will impose larger fitness costs than mutations that affect fewer traits. Here we present a systems approach to test this expectation. Previous studies have independently estimated fitness and morphological effects of deleting all nonessential genes in Saccharomyces cerevisiae. Using datasets generated by these studies, we examined the relationship between the pleiotropic effect of each deletion mutation, measured as the number of morphological traits differing from the parental strain, and its effect on fitness. Pleiotropy explained ,18% of variation in fitness among the mutants even once we controlled for correlations between morphological traits. This relationship was robust to consideration of other explanatory factors, including the number of protein,protein interactions and the network position of the deleted genes. These results are consistent with pleiotropy having a direct role in affecting fitness. [source]


Predator,prey interactions in river networks: comparing shrimp spatial refugia in two drainage basins

FRESHWATER BIOLOGY, Issue 3 2009
ALAN P. COVICH
Summary 1.,Analysis of drainage networks provides a framework to evaluate the densities and distributions of prey species relative to locations of their predators. Upstream migration by diadromous shrimp (Atya lanipes and Xiphocaris elongata) during their life cycle provides access to headwater refugia from fish predation, which is intense in estuaries and coastal rivers. 2.,We postulate that geomorphic barriers (such as large, steep waterfalls >3.5 m in height), can directly limit the distribution of predatory fishes and, indirectly, affect the densities of their prey (freshwater shrimps) in headwater streams. 3.,We compared densities of shrimp in pools above and below waterfalls, in four headwater tributaries in two river basins of the Luquillo Mountains of northeastern Puerto Rico. We measured shrimp densities twice a year over 8 years (1998,2005) in Prieta, Toronja, Bisley 3 and Bisley 5 streams, which differ in drainage network positions relative to steep waterfalls in Río Espíritu Santo and Río Mameyes. 4.,Predatory fishes are absent in the Prieta and Toronja pools and present in Bisely 3 and in lower Bisley 5 pools. Atya lanipes and X. elongata rarely occur in the Bisley streams where predatory fishes are present but these shrimps are abundant in Prieta and Toronja, streams lacking predatory fishes. 5.,The mean carapace length of X. elongata is longer in pools where fish are present (Bisley 3 and lower Bisley 5) than in pools lacking fish (Prieta, Toronja, Upper Bisley 5). The increased body size is primarily due to significantly longer rostrums of individuals in stream reaches with fish (below waterfall barriers) than in those reaches lacking fish (above waterfall barriers). Rostrum length may be an adaptation to avoid predation by visually feeding fishes. 6.,Atya lanipes and X. elongata distributions and densities were predicted primarily by drainage network position relative to the presence or absence of predatory fishes. High, steep waterfalls effectively impeded fish from moving upstream and created a spatial refuge. Xiphocaris elongata may rely on size refugia (longer rostrum) to minimize predation where spatial refugia are lacking. [source]


Private Equity Syndication: Agency Costs, Reputation and Collaboration

JOURNAL OF BUSINESS FINANCE & ACCOUNTING, Issue 5-6 2009
Miguel Meuleman
Abstract:, Syndicates are a form of inter-firm alliance in which two or more private equity firms invest together in an investee firm and share a joint pay-off, and are an enduring feature of the leveraged buyout (LBO) and private equity industry. This study examines the relationship between syndication and agency costs at the investor-investee level, and the extent to which the reputation and the network position of the lead investor mediate this relationship. We examine this relationship using a sample of 1,122 buyout investments by 80 private equity companies in the UK between 1993 and 2006. Our findings show that where agency costs are highest, and hence ex-post monitoring by the lead investor is more important, syndication is less likely to occur. The negative relationship between agency costs and syndication, however, is alleviated by the reputation and network position of the lead investor firm. [source]


The impact of relative tenure on newcomer socialization dynamics

JOURNAL OF ORGANIZATIONAL BEHAVIOR, Issue 7 2004
Keith Rollag
Although many researchers have examined the impact of organizational tenure on newcomer socialization dynamics, few have explored whether relative tenure influences perceptions and behaviors inside organizations. This study introduces the concept of relative tenure and shows through a sociometric survey of 200 employees across four organizations that an individual's relative position in his or her firm's tenure distribution explains a significantly greater percentage of variance in newcomer status, social network position, and information-providing behavior than does absolute measures of tenure. The results suggest that organizational growth and turnover may have a bigger impact on newcomer socialization dynamics than has been discussed in the literature. The implications of the findings for socialization researchers and managers are discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Predator,prey interactions in river networks: comparing shrimp spatial refugia in two drainage basins

FRESHWATER BIOLOGY, Issue 3 2009
ALAN P. COVICH
Summary 1.,Analysis of drainage networks provides a framework to evaluate the densities and distributions of prey species relative to locations of their predators. Upstream migration by diadromous shrimp (Atya lanipes and Xiphocaris elongata) during their life cycle provides access to headwater refugia from fish predation, which is intense in estuaries and coastal rivers. 2.,We postulate that geomorphic barriers (such as large, steep waterfalls >3.5 m in height), can directly limit the distribution of predatory fishes and, indirectly, affect the densities of their prey (freshwater shrimps) in headwater streams. 3.,We compared densities of shrimp in pools above and below waterfalls, in four headwater tributaries in two river basins of the Luquillo Mountains of northeastern Puerto Rico. We measured shrimp densities twice a year over 8 years (1998,2005) in Prieta, Toronja, Bisley 3 and Bisley 5 streams, which differ in drainage network positions relative to steep waterfalls in Río Espíritu Santo and Río Mameyes. 4.,Predatory fishes are absent in the Prieta and Toronja pools and present in Bisely 3 and in lower Bisley 5 pools. Atya lanipes and X. elongata rarely occur in the Bisley streams where predatory fishes are present but these shrimps are abundant in Prieta and Toronja, streams lacking predatory fishes. 5.,The mean carapace length of X. elongata is longer in pools where fish are present (Bisley 3 and lower Bisley 5) than in pools lacking fish (Prieta, Toronja, Upper Bisley 5). The increased body size is primarily due to significantly longer rostrums of individuals in stream reaches with fish (below waterfall barriers) than in those reaches lacking fish (above waterfall barriers). Rostrum length may be an adaptation to avoid predation by visually feeding fishes. 6.,Atya lanipes and X. elongata distributions and densities were predicted primarily by drainage network position relative to the presence or absence of predatory fishes. High, steep waterfalls effectively impeded fish from moving upstream and created a spatial refuge. Xiphocaris elongata may rely on size refugia (longer rostrum) to minimize predation where spatial refugia are lacking. [source]


Investigation of the distributed generation penetration in a medium voltage power distribution network

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 7 2010
G. N. Koutroumpezis
Abstract This paper investigates the results of the distributed generation penetration in a weak medium voltage power distribution network. The connected distributed generation resources are in their entirety small hydroelectric plants. Their locations are predetermined. Specifically, the influence of distributed generation on the network branch currents and voltage profile as well as on the short-circuit level at the medium voltage busbars of the infeeding substation are examined using a commercial-grade software package. The arising problems are explored and alternative technical solutions to deal with them are proposed. Finally, an initial proposal for an optimum distributed generation penetration in the predetermined network positions is given. A real-world study case, rather than a simplified academic network, is selected to be analysed in order to specify, as accurately as possible, the arising practical problems and to use this experience in the future in the development of a fast and reliable method for the determination of optimal distributed generation allocation in random network positions. Copyright © 2009 John Wiley & Sons, Ltd. [source]