260 research outputs found
Tuning a fuzzy controller using quadratic response surfaces
Response surface methodology, an alternative method to traditional tuning of a fuzzy controller, is described. An example based on a simulated inverted pendulum 'plant' shows that with (only) 15 trial runs, the controller can be calibrated using a quadratic form to approximate the response surface
Small ecologies
Small ecologies is a poetry collection that explores the interconnectedness of all aspects of life, from microscopic neural synapses to macroscopic cosmic occurrences. Strongly influenced, but not constrained, by the natural world, the poems in Small ecologies delve into the deep regions of human interaction with the environment, other humans, and themselves. The large ecology in which humans exist is created by an infinite number of small ecologies
Photoionization of Clustered Halos by the First Stars
We present numerical simulations of the photoevaporation of cosmological
halos clustered around a 120 M primordial star, confining our study to
structures capable of hosting Population III star formation. The calculations
include self-consistent multifrequency conservative transfer of UV photons
together with nine-species primordial chemistry and all relevant radiative
processes. The ultimate fates of these halos varies with central density and
proximity to the central source but generally fall into one of four categories.
Diffuse halos with central densities below 2 - 3 cm are completely
ionized and evaporated by the central star anywhere in the cluster. More
evolved halo cores at densities above 2000 cm are impervious to both
ionizing and Lyman-Werner flux at most distances from the star and collapse of
their cores proceeds without delay. Radiative feedback in halos of intermediate
density can be either positive or negative, depending on how the I-front
remnant shock both compresses and deforms the core and enriches it with H.
We find that the 120 M star photodissociates H in most halos within
the cluster but that catalysis by H- rapidly restores molecular hydrogen within
a few hundred Kyr after the death of the star, with little delay in star
formation. Our models exhibit significant departures from previous
one-dimensional spherically-symmetric simulations, which are prone to serious
errors due to unphysical geometric focusing effects.Comment: 5 pages, 5 figures, to appear in "First Stars III", eds. B. O'Shea,
A. Heger and T. Abe
How the First Stars Regulated Local Star Formation I: Radiative Feedback
We present numerical simulations of how a 120 M primordial star
regulates star formation in nearby cosmological halos at 20 by
photoevaporation. Our models include nine-species primordial chemistry and
self-consistent multifrequency conservative transfer of UV photons with all
relevant radiative processes. Whether or not new stars form in halos clustered
around a Population III star ultimately depends on their core densities and
proximity to the star. Diffuse halos with central densities below 2 - 3
cm are completely ionized and evaporated anywhere in the cluster.
Evolved halos with core densities above 2000 cm are impervious to both
ionizing and Lyman-Werner flux at most distances from the star and collapse as
quickly as they would in its absence. Star formation in halos of intermediate
density can be either promoted or suppressed depending on how the I-front
remnant shock compresses, deforms and enriches the core with H. We find
that the 120 M star photodissociates H in most halos in the cluster
but that catalysis by H- restores it a few hundred kyr after the death of the
star, with little effect on star formation. Our models exhibit significant
departures from previous one-dimensional spherically-symmetric simulations,
which are prone to serious errors due to unphysical geometric focusing effects.Comment: 20 pages, 19 figures, accepted by ApJ, title and abstract change
Forming a Primordial Star in a Relic HII Region
There has been considerable theoretical debate over whether photoionization
and supernova feedback from the first Population III stars facilitate or
suppress the formation of the next generation of stars. We present results from
an Eulerian adaptive mesh refinement simulation demonstrating the formation of
a primordial star within a region ionized by an earlier nearby star. Despite
the higher temperatures of the ionized gas and its flow out of the dark matter
potential wells, this second star formed within 23 million years of its
neighbor's death. The enhanced electron fraction within the HII region
catalyzes rapid molecular hydrogen formation that leads to faster cooling in
the subsequent star forming halos than in the first halos. This "second
generation" primordial protostar has a much lower accretion rate because,
unlike the first protostar, it forms in a rotationally supported disk of
approx. 10-100 solar masses. This is primarily due to the much higher angular
momentum of the halo in which the second star forms. In contrast to previously
published scenarios, such configurations may allow binaries or multiple systems
of lower mass stars to form. These first high resolution calculations offer
insight into the impact of feedback upon subsequent populations of stars and
clearly demonstrate how primordial chemistry promotes the formation of
subsequent generations of stars even in the presence of the entropy injected by
the first stars into the IGM.Comment: 4 pages, 2 figures. Some revisions, including enhanced discussion of
angular momentum issues. Asrophysical Journal, accepte
Multiscale Object-Based Classification and Feature Extraction along Arctic Coasts
Permafrost coasts are experiencing accelerated erosion in response to above average warming in the Arctic resulting in local, regional, and global consequences. However, Arctic coasts are expansive in scale, constituting 30–34% of Earth’s coastline, and represent a particular challenge for wide-scale, high temporal measurement and monitoring. This study addresses the potential strengths and limitations of an object-based approach to integrate with an automated workflow by assessing the accuracy of coastal classifications and subsequent feature extraction of coastal indicator features. We tested three object-based classifications; thresholding, supervised, and a deep learning model using convolutional neural networks, focusing on a Pleaides satellite scene in the Western Canadian Arctic. Multiple spatial resolutions (0.6, 1, 2.5, 5, 10, and 30 m/pixel) and segmentation scales (100, 200, 300, 400, 500, 600, 700, and 800) were tested to understand the wider applicability across imaging platforms. We achieved classification accuracies greater than 85% for the higher image resolution scenarios using all classification methods. Coastal features, waterline and tundra, or vegetation, line, generated from image classifications were found to be within the image uncertainty 60% of the time when compared to reference features. Further, for very high resolution scenarios, segmentation scale did not affect classification accuracy; however, a smaller segmentation scale (i.e., smaller image objects) led to improved feature extraction. Similar results were generated across classification approaches with a slight improvement observed when using deep learning CNN, which we also suggest has wider applicability. Overall, our study provides a promising contribution towards broad scale monitoring of Arctic coastal erosion.info:eu-repo/semantics/publishedVersio
Contributors to Dining Satisfaction of Residence Hall Students
Early writings on university housing show a connection between dining services and university residence halls (Riker & Lopez, 1 96 1 ) Regardless of how housing and dining programs are organized within the institution, the two entities are inevitably connected; living and eating go together. A recent annual study (Educational Benchmarking, Inc. (EBI), 2002) comparing four years of data cited satisfaction with dining as being one of the foremost predictors of overall residence satisfaction. This prominent relationship provides incentive for housing administrators to be more aware of students\u27 dining satisfaction. The purpose of this research was to examine contributors to residence hall students\u27 dining satisfaction at a large Midwestern university
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