855 research outputs found
COMPARISON OF CONVENTIONAL AND TRANSGENIC TECHNOLOGIES UNDER ALTERNATIVE CULTURAL PRACTICES FOR COTTON IN GEORGIA
This study was conducted to determine allocative efficiency and cost effectiveness of growing conventional and transgenic cotton varieties under alternative cultural practices in South Georgia. A data envelopment model was used to compare costs and returns associated with various combinations of tillage and technology. The results suggest that combination of genetically modified cotton varieties and strip till cultivation practices yields a more efficient use of inputs relative to the level of output.Crop Production/Industries, Research and Development/Tech Change/Emerging Technologies,
The products of hydrolysis of cascara resin
Thesis (B.S.)--University of Illinois, 1920.Typescript.Includes bibliographical references (leaf 13)
Tests of efficiency of the Rolla power plant
The object of the test was to determine the efficiency of the separate units and of the plant as a whole under actual normal working conditions --Object, page 1
Migration of Extrasolar Planets: Effects from X-Wind Accretion Disks
Magnetic fields are dragged in from the interstellar medium during the
gravitational collapse that forms star/disk systems. Consideration of mean
field magnetohydrodynamics (MHD) in these disks shows that magnetic effects
produce subkeplerian rotation curves and truncate the inner disk. This letter
explores the ramifications of these predicted disk properties for the migration
of extrasolar planets. Subkeplerian flow in gaseous disks drives a new
migration mechanism for embedded planets and modifies the gap opening processes
for larger planets. This subkeplerian migration mechanism dominates over Type I
migration for sufficiently small planets (m_P < 1 M_\earth) and/or close orbits
(r < 1 AU). Although the inclusion of subkeplerian torques shortens the total
migration time by only a moderate amount, the mass accreted by migrating
planetary cores is significantly reduced. Truncation of the inner disk edge
(for typical system parameters) naturally explains final planetary orbits with
periods P=4 days. Planets with shorter periods P=2 days can be explained by
migration during FU-Ori outbursts, when the mass accretion rate is high and the
disk edge moves inward. Finally, the midplane density is greatly increased at
the inner truncation point of the disk (the X-point); this enhancement, in
conjunction with continuing flow of gas and solids through the region, supports
the in situ formation of giant planets.Comment: 15 pages, 2 figures, accepted to ApJ Letter
Effects of Turbulence, Eccentricity Damping, and Migration Rate on the Capture of Planets into Mean Motion Resonance
Pairs of migrating extrasolar planets often lock into mean motion resonance
as they drift inward. This paper studies the convergent migration of giant
planets (driven by a circumstellar disk) and determines the probability that
they are captured into mean motion resonance. The probability that such planets
enter resonance depends on the type of resonance, the migration rate, the
eccentricity damping rate, and the amplitude of the turbulent fluctuations.
This problem is studied both through direct integrations of the full 3-body
problem, and via semi-analytic model equations. In general, the probability of
resonance decreases with increasing migration rate, and with increasing levels
of turbulence, but increases with eccentricity damping. Previous work has shown
that the distributions of orbital elements (eccentricity and semimajor axis)
for observed extrasolar planets can be reproduced by migration models with
multiple planets. However, these results depend on resonance locking, and this
study shows that entry into -- and maintenance of -- mean motion resonance
depends sensitively on migration rate, eccentricity damping, and turbulence.Comment: 43 pages including 14 figures; accepted for publication in The
Astrophysical Journa
Buckling and vibration analysis of laminated panels using VICONOPT
The analysis aspects of the 23,000‐line FORTRAN program VICONOPT are described. Overall stiffness matrices assembled from the earlier exact VIPASA flat plate stiffnesses are optionally coupled by Lagrangian multipliers to find critical buckling loads, or natural frequencies of undamped vibration, of prismatic assemblies of anisotropic flat plates with arbitrarily located point supports or simple transverse supporting frames. The longitudinal continuity of typical wing and fuselage panels is closely approximated because the solutions are for the infinitely long structure obtained by repeating a bay and its supports longitudinally. Any longitudinally invariant in‐plane plate stresses are permitted, and very rapid solutions are guaranteed by numerous refinements, including multilevel substructuring and a method for repetitive cross sections that is exact for regular polygons used to represent cylinders. Modal displacements and stresses in or between plies of laminated plates are calculated and plotted, with values being recovered at all nodes of substructures. Comparison with usual approximate finite‐element methods confirms that, for comparably converged solutions, VICONOPT is typically between 100 and 104 times faster
Subject preferences of fifth-grade children.
Thesis (Ed.M.)--Boston University
N.B.:Pages 155 and 309 are missing from original thesis
Giant Planet Migration through the Action of Disk Torques and Planet Scattering
This paper presents a parametric study of giant planet migration through the
combined action of disk torques and planet-planet scattering. The torques
exerted on planets during Type II migration in circumstellar disks readily
decrease the semi-major axes, whereas scattering between planets increases the
orbital eccentricities. This paper presents a parametric exploration of the
possible parameter space for this migration scenario using two (initial)
planetary mass distributions and a range of values for the time scale of
eccentricity damping (due to the disk). For each class of systems, many
realizations of the simulations are performed in order to determine the
distributions of the resulting orbital elements of the surviving planets; this
paper presents the results of 8500 numerical experiments. Our goal is to study
the physics of this particular migration mechanism and to test it against
observations of extrasolar planets. The action of disk torques and
planet-planet scattering results in a distribution of final orbital elements
that fills the a-e plane, in rough agreement with the orbital elements of
observed extrasolar planets. In addition to specifying the orbital elements, we
characterize this migration mechanism by finding the percentages of ejected and
accreted planets, the number of collisions, the dependence of outcomes on
planetary masses, the time spent in 2:1 and 3:1 resonances, and the effects of
the planetary IMF. We also determine the distribution of inclination angles of
surviving planets and the distribution of ejection speeds for exiled planets.Comment: 46 pages including 15 figures; accepted to ICARU
Combining multiple classifications of chemical structures using consensus clustering
Consensus clustering involves combining multiple clusterings of the same set of objects to achieve a single clustering that will, hopefully, provide a better picture of the groupings that are present in a dataset. This Letter reports the use of consensus clustering methods on sets of chemical compounds represented by 2D fingerprints. Experiments with DUD, IDAlert, MDDR and MUV data suggests that consensus methods are unlikely to result in significant improvements in clustering effectiveness as compared to the use of a single clustering method. (C) 2012 Elsevier Ltd. All rights reserved
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