3,487 research outputs found

    Deterministic Small-World Networks

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    Many real life networks, such as the World Wide Web, transportation systems, biological or social networks, achieve both a strong local clustering (nodes have many mutual neighbors) and a small diameter (maximum distance between any two nodes). These networks have been characterized as small-world networks and modeled by the addition of randomness to regular structures. We show that small-world networks can be constructed in a deterministic way. This exact approach permits a direct calculation of relevant network parameters allowing their immediate contrast with real-world networks and avoiding complex computer simulations.Comment: 6 pages, 1 figur

    DATAMAP upgrade version 4.0

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    The changes made on the data analysis and management program DATAMAP (Data from Aeromechanics Test and Analytics - Management and Analysis Package) are detailed. These changes are made to Version 3.07 (released February, 1981) and are called Version 4.0. Version 4.0 improvements were performed by Sterling Software under contract to NASA Ames Research Center. The increased capabilities instituted in this version include the breakout of the source code into modules for ease of modification, addition of a more accurate curve fit routine, ability to handle higher frequency data, additional data analysis features, and improvements in the functionality of existing features. These modification will allow DATAMAP to be used on more data sets and will make future modifications and additions easier to implement

    Oil, Development, and the Politics of the Bottom Billion

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    Cascade Dynamics of Multiplex Propagation

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    Random links between otherwise distant nodes can greatly facilitate the propagation of disease or information, provided contagion can be transmitted by a single active node. However we show that when the propagation requires simultaneous exposure to multiple sources of activation, called multiplex propagation, the effect of random links is just the opposite: it makes the propagation more difficult to achieve. We calculate analytical and numerically critical points for a threshold model in several classes of complex networks, including an empirical social network.Comment: 4 pages, 5 figures, for similar work visit http://hsd.soc.cornell.edu and http://www.imedea.uib.es/physdep

    Investigation into the Potential Use of Windbreaks to Improve Solar Collector Performance

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    The global demand for energy is ever increasing; however, the world has a limited number of fossil fuels available. Therefore, alternative renewable energy sources must be utilized. For this reason, solar thermal collectors have become an increasingly popular method for providing hot water or space heating. However, solar thermal collectors are most commonly used in areas that experience warm climates throughout the year. In areas that experience seasonal climates, the cold temperatures and harsh climate conditions significantly reduce the performance of solar thermal collectors during the winter months. This thesis examined the potential that the implementation of a windbreak could have on improving the performance of a solar collector, by reducing the wind induced convection losses, during winter climate conditions. In order to determine the effect of the windbreak, two collectors were operated simultaneously and side by side, one of which had a windbreak. The expected wind direction was from the northwest, so the windbreak was positioned on the westward side of the eastward collector. In this position, a northwest wind would pass over the first collector unhindered and the windbreak would provide shelter to the second collector. The performance of two collectors was measured by calculating and comparing the instantaneous efficiencies. Data was collected during February 2010 and October and November 2010. The results indicated that both wind speed and wind direction will impact the effect that the windbreak has. As one would expect, during non-windy days there was no significant difference observed between the two collectors. On Windy days in which the wind came from the expected wind direction, the windbreak appeared improve the collector\u27s performance. However, due to the uncertainty in the measurements, and the limited number of data points, a definitive declaration cannot be made

    Time Allocations and Reward Structures for US Academic Economists from 1955–2005: Evidence from Three National Surveys

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    Using survey data collected in 1995, 2000 and 2005 from US academic economists, in which respondents were asked to indicate what percentage of their work time they allocate to research, teaching and service activities, and also how their departments and schools weight research, teaching and service in determining annual raises and making promotion and tenure decisions, we find these economists were allocating more time to teaching even though perceived departmental and school incentives provided a clear premium for research. The overall samples did not show major changes in their allocation of time from 1995–2005, but there were different responses at different types of schools, with increased time spent on research by faculty at doctoral schools while at masters' and baccalaureate schools more time was devoted to teaching. We use regression analysis to investigate factors that affect how different faculty members allocate their time between teaching and research. In addition to Carnegie school classifications and related school characteristics, faculty members' gender and rank were significant predictors of how economists allocate their time. Male economists, particularly among assistant professors at research universities, spent less time on teaching and more time on research than female economists.
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