1,530 research outputs found
How ripples turn into dots: modeling ion-beam erosion under oblique incidence
Pattern formation on semiconductor surfaces induced by low energetic ion-beam
erosion under normal and oblique incidence is theoretically investigated using
a continuum model in form of a stochastic, nonlocal, anisotropic
Kuramoto-Sivashinsky equation. Depending on the size of the parameters this
model exhibits hexagonally ordered dot, ripple, less regular and even rather
smooth patterns. We investigate the transitional behavior between such states
and suggest how transitions can be experimentally detected.Comment: 11 pages, 4 figures, submitted for publication, revised versio
Far-infrared photometric observations of the outer planets and satellites with Herschel-PACS
We present all Herschel PACS photometer observations of Mars, Saturn, Uranus,
Neptune, Callisto, Ganymede, and Titan. All measurements were carefully
inspected for quality problems, were reduced in a (semi-)standard way, and were
calibrated. The derived flux densities are tied to the standard PACS photometer
response calibration, which is based on repeated measurements of five fiducial
stars. The overall absolute flux uncertainty is dominated by the estimated 5%
model uncertainty of the stellar models in the PACS wavelength range between 60
and 210 micron. A comparison with the corresponding planet and satellite models
shows excellent agreement for Uranus, Neptune, and Titan, well within the
specified 5%. Callisto is brighter than our model predictions by about 4-8%,
Ganymede by about 14-21%. We discuss possible reasons for the model offsets.
The measurements of these very bright point-like sources, together with
observations of stars and asteroids, show the high reliability of the PACS
photometer observations and the linear behavior of the PACS bolometer source
fluxes over more than four orders of magnitude (from mJy levels up to more than
1000 Jy). Our results show the great potential of using the observed solar
system targets for cross-calibration purposes with other ground-based,
airborne, and space-based instruments and projects. At the same time, the PACS
results will lead to improved model solutions for future calibration
applications.Comment: 25 pages, 11 figures, 11 table
Influence of the Dufour effect on convection in binary gas mixtures
Linear and nonlinear properties of convection in binary fluid layers heated
from below are investigated, in particular for gas parameters. A Galerkin
approximation for realistic boundary conditions that describes stationary and
oscillatory convection in the form of straight parallel rolls is used to
determine the influence of the Dufour effect on the bifurcation behaviour of
convective flow intensity, vertical heat current, and concentration mixing. The
Dufour--induced changes in the bifurcation topology and the existence regimes
of stationary and traveling wave convection are elucidated. To check the
validity of the Galerkin results we compare with finite--difference numerical
simulations of the full hydrodynamical field equations. Furthermore, we report
on the scaling behaviour of linear properties of the stationary instability.Comment: 14 pages and 10 figures as uuencoded Postscript file (using uufiles
Spring Dispersal Patterns of Red-winged Blackbirds, \u3ci\u3eAgelaius phoeniceus\u3c/i\u3e, staging in Eastern South Dakota
Red-winged Blackbirds (Agelaius phoeniceus) are very abundant summer residents throughout the Prairie Pothole Region of central Norht America. In late summer they assemble in post-breeding flocks that cause significant amounts of agricultural damage, particularly in sunflower fields near natal sites. In April 2001, we aerially color-marked ~370,000 Red-winged Blackbirds near Badger, South Dakota (44°48\u27N, 97°21\u27W), to determine if migrants staging here were summer residents in sunflower production areas ~350 km to the northwest. We measured patterns of migratory dispersal by collecting birds in 54 randomly selected blocks in the north central U.S. and the Prairie Provinces of Canada. The marked specimens (n =33) were categorized into three polygons based on analyses of banding and re-sighting data and proximity to concentrated sunflower production. We estimated that 82% of the migrants that had staged in eastern South Dakota resided within or on the periphery of the sunflower growing area. These birds probably stay near their breeding territories until at least late August and cause early damage to sunflower, which comprises the majority of damage. Resident birds in Alberta and most of Saskatchewan (18%) might arrive too late in the damage season to impact the sunflower crop significantly
Evaluation of registered pesticides as repellents for reducing blackbird (Icteridae) damage to sunflower
Chemical feeding repellents applied to ripening sunflower might help reduce blackbird (Icteridae) damage, which is a chronic agricultural problem from seed formation to harvest. However, costs are high to develop and register new repellents for agricultural use. In 2003 and 2004, we evaluated feeding repellency of 8 pesticides registered by the Environmental Protection Agency for use in sunflower. Caged red-winged blackbirds (Agelaius phoeniceus) were fed unshelled sunflower seeds treated with the following pesticides: 5 pyrethroid insecticides, an organochlorine, an organophosphorus, and a fungicide. Compared to untreated reference groups, feeding rates were reduced for 4 of the 5 pyrethroid insecticides. Only the organophosphorus (chlorpyrifos), however, significantly decreased feeding rates. More research on repellency effects of this product in field efficacy trials is probably warranted based on the results of our cage experiments. Depending on timing of application, registered insecticides with blackbird feeding repellency could provide supplemental economic benefits to sunflower producers through dual purpose use
Amorphous thin film growth: theory compared with experiment
Experimental results on amorphous ZrAlCu thin film growth and the dynamics of
the surface morphology as predicted from a minimal nonlinear stochastic
deposition equation are analysed and compared. Key points of this study are (i)
an estimation procedure for coefficients entering into the growth equation and
(ii) a detailed analysis and interpretation of the time evolution of the
correlation length and the surface roughness. The results corroborate the
usefulness of the deposition equation as a tool for studying amorphous growth
processes.Comment: 7 pages including 5 figure
Spring Dispersal Patterns of Red-winged Blackbirds, Agelaius phoeniceus, Staging in Eastern South Dakota
Red-winged Blackbirds (Agelaius phoeniceus) are very abundant summer residents throughout the Prairie Pothole Region of central North America. In late summer they assemble in post-breeding flocks that cause significant amounts of agricultural damage, particularly in sunflower fields near natal sites. In April 2001, we aerially color-marked ~370,000 Red-winged Blackbirds near Badger, South Dakota (44°48'N, 97°21'W), to determine if migrants staging here were summer residents in sunflower production areas ~350 km to the northwest. We measured patterns of migratory dispersal by collecting birds in 54 randomly selected blocks in the northcentral U.S. and the Prairie Provinces of Canada. The marked specimens (n = 33) were categorized into three polygons based on analyses of banding and re-sighting data and proximity to concentrated sunflower production. We estimated that 82% of the migrants that had staged in eastern South Dakota resided within or on the periphery of the sunflower growing area. These birds probably stay near their breeding territories until at least late August and cause early damage to sunflower, which comprises the majority of damage. Resident birds in Alberta and most of Saskatchewan (18%) might arrive too late in the damage season to impact the sunflower crop significantly
Influence of the Soret effect on convection of binary fluids
Convection in horizontal layers of binary fluids heated from below and in
particular the influence of the Soret effect on the bifurcation properties of
extended stationary and traveling patterns that occur for negative Soret
coupling is investigated theoretically. The fixed points corresponding to these
two convection structures are determined for realistic boundary conditions with
a many mode Galerkin scheme for temperature and concentration and an accurate
one mode truncation of the velocity field. This solution procedure yields the
stable and unstable solutions for all stationary and traveling patterns so that
complete phase diagrams for the different convection types in typical binary
liquid mixtures can easily be computed. Also the transition from weakly to
strongly nonlinear states can be analyzed in detail. An investigation of the
concentration current and of the relevance of its constituents shows the way
for a simplification of the mode representation of temperature and
concentration field as well as for an analytically manageable few mode
description.Comment: 30 pages, 12 figure
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