13,905 research outputs found

    Anisotropic evolution of D-dimensional FRW spacetime

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    We examine the time evolution of the D=d+4 dimensional Einstein field equations subjected to a flat Robertson-Walker metric where the 3D and higher-dimensional scale factors are allowed to evolve at different rates. We find the exact solution to these equations for a single fluid component, which yields two limiting regimes offering the 3D scale factor as a function of the time. The fluid regime solution closely mimics that described by 4D FRW cosmology, offering a late-time behavior for the 3D scale factor after becoming valid in the early universe, and can give rise to a late-time accelerated expansion driven by vacuum energy. This is shown to be preceded by an earlier volume regime solution, which offers a very early-time epoch of accelerated expansion for a radiation-dominated universe for d=1. The time scales describing these phenomena, including the transition from volume to fluid regime, are shown to fall within a small fraction of the first second when the fundamental constants of the theory are aligned with the Planck time. This model potentially offers a higher-dimensional alternative to scalar-field inflationary theory and a consistent cosmological theory, yielding a unified description of early- and late-time accelerated expansions via a 5D spacetime scenario.Comment: Title changed from "A possible higher-dimensional alternative to scalar-field inflationary theory". Several new results have been added including a predicted lower- and upper-bound on the time scales marking the end of an early-time inflationary epoch and the beginning of an FRW epoch for d=

    Meteorological satellite data: A tool to describe the health of the world's agriculture

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    Local area coverage data acquired aboard the TIROS-N satellite family by the advanced very high resolution radiometer systems was examined to determine the agricultural information current. Albedo differences between channel 2 and channel 1 of the advanced very high resolution radiometer LAC (called EVI) are shown to be closely correlated to the Ashburn vegetative index produced from LANDSAT multispectral scanner data which have been shown to vary in response to "greenness", soil moisture, and crop production. The statistical correlation between the EVI and the Ashburn Vegetative Index (+ or - 1 deg) is 0.86

    Analysis of fluid/mechanical systems using EASY5

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    This paper illustrates how the use of a general analysis package can simplify modeling and analyzing fluid/mechanical systems. One such package is EASY5, a Boeing Computer Services product. The basic transmission line equations for modeling piped fluid systems are presented, as well as methods of incorporating these equations into the EASY5 environment. The paper describes how this analysis tool has been used to model several fluid subsystems of the Space Shuttle Orbiter

    Introduction to Special Issue of \u3ci\u3eJournal of Defense Modeling and Simulation\u3c/i\u3e: Novel Approaches to Defense and Military Modeling and Simulation

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    Developing solutions to complex problems in government and industry is a daunting task that often requires tremendous investment in time and resources to solve. Modeling and simulation (M&S) has incredible potential to streamline development and cut costs by conducting virtual experiments that give insight into performance under various test conditions. As many program managers in the federal acquisition process can attest, realistic testing of live equipment in an operational environment can be some of the most expensive parts of a development program. M&S can provide insight into mission success of yetto- bedesigned systems without the need to actually build and test the system in the real world. Similarly, M&S tools can evaluate human effectiveness under various scenarios while only risking the virtual lives of avatars. When properly applied, M&S capabilities provide critical insight that allows leaders to make smart decisions about how to accomplish the mission and increase human performance more quickly and at lower cost and risk than reliance on real-world testing. Throughout this special issue, we examine a variety of novel M&S concepts that promise to deliver simulation results to the defense and military community that positively impact system-level mission studies and human effectiveness research. These M&S tools not only affect the defense and military community, but can also have application to a wide variety of government and industry users with needs to solve similar problem sets. Whether the end goal is cost savings, operational analysis or refinement of sub-components, the M&S concepts described in this special issue testify to the power that these tools can provide to help decision makers efficiently allocate scarce resources and provide improved performance of humans and the systems that they operate in the long run
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