4,840 research outputs found
A computer simulation of Skylab dynamics and attitude control for performance verification and operational support
A simulation of the Skylab attitude and pointing control system (APCS) is outlined and discussed. Implementation is via a large hybrid computer and includes those factors affecting system momentum management, propellant consumption, and overall vehicle performance. The important features of the flight system are discussed; the mathematical models necessary for this treatment are outlined; and the decisions involved in implementation are discussed. A brief summary of the goals and capabilities of this tool is also included
Plasmon Evolution and Charge-Density Wave Suppression in Potassium Intercalated Tantalum Diselenide
We have investigated the influence of potassium intercalation on the
formation of the charge-density wave (CDW) instability in 2H-tantalum
diselenide by means of Electron Energy-Loss Spectroscopy and density functional
theory. Our observations are consistent with a filling of the conduction band
as indicated by a substantial decrease of the plasma frequency in experiment
and theory. In addition, elastic scattering clearly points to a destruction of
the CDW upon intercalation as can be seen by a vanishing of the corresponding
superstructures. This is accompanied by a new superstructure, which can be
attributed to the intercalated potassium. Based on the behavior of the c-axis
upon intercalation we argue in favor of interlayer-sites for the alkali-metal
and that the lattice remains in the 2H-modification
A Bayesian approach to probabilistic sensitivity analysis in structured benefit-risk assessment
Research on irrigation of corn and soybeans at Conesville and Ankeny, Iowa, 1951 to 1955
Irrigation in the humid and semihumid sections of the United States has increased manyfold since World War II. Before this, irrigation was confined principally to the more arid western states. Some of the reasons for the spread to more humid areas were the development of portable lightweight aluminum pipe and couplers, moderately high farm prices, occurrence of several drouthy seasons, increased use of fertilizers and development of better crop varieties. Drouths in various portions of the state in 1953, 1954, 1955 and 1956 have prompted many farmers to buy irrigation equipment. A 1953 survey in Iowa showed that only 55 farmers were irrigating about 3,600 acres. Twenty-two of these farmers were in Muscatine County where irrigation is used on vegetable crops. Two years later, in 1955, another survey indicated that 250 farmers were irrigating approximately 15,000 acres.
Indications are that irrigation will continue to increase, particularly along the Mississippi and Missouri rivers. Along the Missouri River there are about 600,000 acres of bottomland. Most of this area needs better surface drainage. Without too much additional cost, land which is surface drained can be shaped for surface irrigation. Because of good ground water supplies, this area has a high irrigation potential. These conditions also exist to a more limited extent along other major Iowa streams
Variability in Short Gamma-ray Bursts: Gravitationally Unstable Tidal Tails
Short gamma-ray bursts are thought to result from the mergers of two neutron
stars or a neutron star and stellar mass black hole. The final stages of the
merger are generally accompanied by the production of one or more tidal "tails"
of ejecta, which fall back onto the remnant-disc system at late times. Using
the results of a linear stability analysis, we show that if the material
comprising these tails is modeled as adiabatic and the effective adiabatic
index satisfies , then the tails are gravitationally unstable
and collapse to form small-scale knots. We analytically estimate the properties
of these knots, including their spacing along the tidal tail and the total
number produced, and their effect on the mass return rate to the merger
remnant. We perform hydrodynamical simulations of the disruption of a
polytropic (with the polytropic and adiabatic indices equal), neutron star by a black hole, and find agreement between the predictions of
the linear stability analysis and the distribution of knots that collapse out
of the instability. The return of these knots to the black hole induces
variability in the fallback rate, which can manifest as variability in the
lightcurve of the GRB and -- depending on how rapidly the instability operates
-- the prompt emission. The late-time variability induced by the return of
these knots is also consistent with the extended emission observed in some
GRBs.Comment: Small corrections, additional references included to reflect ApJL
published versio
The longitudinal conductance of mesoscopic Hall samples with arbitrary disorder and periodic modulations
We use the Kubo-Landauer formalism to compute the longitudinal (two-terminal)
conductance of a two dimensional electron system placed in a strong
perpendicular magnetic field, and subjected to periodic modulations and/or
disorder potentials. The scattering problem is recast as a set of
inhomogeneous, coupled linear equations, allowing us to find the transmission
probabilities from a finite-size system computation; the results are exact for
non-interacting electrons. Our method fully accounts for the effects of the
disorder and the periodic modulation, irrespective of their relative strength,
as long as Landau level mixing is negligible. In particular, we focus on the
interplay between the effects of the periodic modulation and those of the
disorder. This appears to be the relevant regime to understand recent
experiments [S. Melinte {\em et al}, Phys. Rev. Lett. {\bf 92}, 036802 (2004)],
and our numerical results are in qualitative agreement with these experimental
results. The numerical techniques we develop can be generalized
straightforwardly to many-terminal geometries, as well as other multi-channel
scattering problems.Comment: 13 pages, 11 figure
Operational Observatory of the catalan sea (OOCS)
The Operational Observatory of the Catalan Sea (OOCS) recently created
by the Operational Oceanography Group at CEAB-CSIC is presented. The OOCS aims
at performing observations of the marine environment in the Catalan Sea and beyond,
assessing, modelling and forecasting the hydrodynamic and biogeochemical
processes of the region. Some of the biogeochemical variables available in the models
and forecast are phytoplankton, zooplankton and nutrients. Although OOCS is
expected to be fully operational in 2011, some of its services are already available to
the public through a dedicated webpage http://www.ceab.csic.es/~simob/.Peer Reviewe
Embedding language across the university and through the curriculum: implementing the EEL project
EVOLUTION OF THE STRATOSPHERIC TEMPERATURE AND CHEMICAL COMPOSITION OVER ONE TITANIAN YEAR
Since the Voyager 1 (V1) flyby in 1980, Titans exploration from space and the ground has been ongoing for more than a full revolution of Saturn around the Sun (one Titan year or 29.5 Earth years was completed in May 2010). In this study we search for temporal variations affecting Titans atmospheric thermal and chemical structure within that year. We process Cassini CIRS data taken during the Titan flybys from 2006-2013 and compare them to the 1980 V1IRIS spectra (re-analyzed here). We also consider data from Earth-based and -orbiting observatories (such as from the ISO, re-visited). When we compare the CIRS 2010 and the IRIS data we find limited inter-annual variations, below the 25 or35 levels for the lower and middle, or the high latitudes, respectively. A return to the 1980 stratospheric temperatures and abundances is generally achieved from 50degN to 50degS, indicative of the solar radiation being the dominating energy source at 10 AU, as for the Earth, as predicted by GCM and photochemical models. However, some exceptions exist among the most complex hydrocarbons (C4H2 and C3H4), especially in the North. In the Southern latitudes, since 2012, we see a trend for an increase of several trace gases, possibly indicative of a seasonal atmospheric reversal. At the Northern latitudes we found enhanced abundances around the period of the northern spring equinox in mid-2009 (as in Bampasidis et al. 2012), which subsequently decreased (from 2010-2012) returning to values similar to those found in the V1 epoch a Titanian year before
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