4,077 research outputs found
Efficiency of Human Activity on Information Spreading on Twitter
Understanding the collective reaction to individual actions is key to
effectively spread information in social media. In this work we define
efficiency on Twitter, as the ratio between the emergent spreading process and
the activity employed by the user. We characterize this property by means of a
quantitative analysis of the structural and dynamical patterns emergent from
human interactions, and show it to be universal across several Twitter
conversations. We found that some influential users efficiently cause
remarkable collective reactions by each message sent, while the majority of
users must employ extremely larger efforts to reach similar effects. Next we
propose a model that reproduces the retweet cascades occurring on Twitter to
explain the emergent distribution of the user efficiency. The model shows that
the dynamical patterns of the conversations are strongly conditioned by the
topology of the underlying network. We conclude that the appearance of a small
fraction of extremely efficient users results from the heterogeneity of the
followers network and independently of the individual user behavior.Comment: 29 pages, 10 figure
Management Roles in Political and Senior Civil Servant Positions: A Multiple-Study Approach
A recent trend in public administration studies has been to assess how public management is performed by politicians and top civil servants. Surprisingly, little is known about how these different posts develop their management roles. Following seminal management studies, we focus on core management roles to compare the ways in which politicians and top civil servants develop their management responsibilities within public organizations. Empirical evidence is provided by triangulating three separate studies developed in Spain. Results from the triangulation show that there is unmistakable evidence of differentiations between politicians and top civil servants when performing their managerial roles
A "Free-Lunch" tour of the Jovian System
An ED-tether mission to Jupiter is presented. A bare tether carrying cathodic devices at both ends but no power supply, and using no propellant, could move 'freely' among Jupiter's
4 great moons. The tour scheme would have current naturally driven throughout by the motional electric field, the Lorentz force switching direction with current around a 'drag' radius of 160,00 kms, where the speed of the jovian ionosphere equals the speed of a spacecraft in circular orbit. With plasma density and magnetic field decreasing rapidly with distance from Jupiter, drag/thrust would only be operated in the inner plasmasphere, current being near shut off conveniently in orbit by disconnecting cathodes or plugging in a very large resistance; the tether could serve as its own power supply by plugging in an electric
load where convenient, with just some reduction in thrust or drag. The periapsis of the spacecraft in a heliocentric transfer orbit from Earth would lie inside the drag sphere; with tether deployed and current on around periapsis, magnetic drag allows Jupiter to capture the spacecraft into an elliptic orbit of high eccentricity. Current would be on at succesive perijove passes and off elsewhere, reducing the eccentricity by lowering the apoapsis progressively to
allow visits of the giant moons. In a second phase, current is on around apoapsis outside the drag sphere, rising the periapsis until the full orbit lies outside that sphere. In a third phase, current is on at periapsis, increasing the eccentricity until a last push makes the orbit hyperbolic to escape Jupiter. Dynamical issues such as low gravity-gradient at Jupiter and tether orientation in elliptic orbits of high eccentricity are discussed
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Saturn power generation with electrodynamic tethers in polar orbit
A power generation scheme based on bare electrodynamic tethers (EDT), working in passive mode is investigated for the purpose of supplying power to scientific missions at Saturn. The system employs a spinning EDT on a lowaltitude
polar orbit which permits to efficiently convert plasmasphere energy into useful power. After optimizing the tether design for power generation we compute the supplied power along the orbit and the impact of the Lorentz force
on the orbital elements as function of the tether and orbit characteristics.
Although uncertainties in the current ionosphere density modeling strongly affect the performance of the system the peak power density of the EDT appears be greater than conventional power systems
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