669 research outputs found
Study of a static screen, jig, spiral, and a compound water cyclone in a placer gold recovery plant
During the 1986 mining season both laboratory and field test work were conducted to study the performance efficiencies of a wedge-wire static screen, a Pan-American jig, a Reichert Mark VII spiral, and a 12" compound water cyclone. This work was conducted at EVECO, Inc.'s placer gold operations near Fox, Alaska, and funded by the State of Alaska Department of Natural Resources. The Mineral Industry Research Laboratory of the University of Alaska-Fairbanks perfomed the test work.Funded by the State of Alaska Department of Natural Resources
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The curious case of the camelthorn: competition, coexistence and nest-site limitation in a multispecies mutualism
Myrmecophyte plants house ants in domatia in exchange for protection from herbivores. Ant-myrmecophyte mutualisms exhibit two general patterns due to competition between ants for plant occupancy: i) domatia nest-sites are a limiting resource and ii) each individual plant hosts one ant species at a time. However, individual camelthorn trees (Vachellia erioloba) typically host two to four ant species simultaneously, often coexisting in adjacent domatia on the same branch. Such fine-grain spatial coexistence brings into question the conventional wisdom on ant-myrmecophyte mutualisms. Camelthorn ants appear not to be nest-site limited, despite low abundance of suitable domatia, and have random distributions of nest-sites within and across trees. These patterns suggest a lack of competition between ants for domatia and contrast strongly with other ant-myrmecophyte systems. Comparison of this unusual case with others suggests that spatial scale is crucial to coexistence or competitive exclusion involving multiple ant species. Furthermore, coexistence may be facilitated when co-occurring ant species diverge strongly on at least one niche axis. Our conclusions provide recommendations for future ant-myrmecophyte research, particularly in utilising multispecies systems to further our understanding of mutualism biology
Explosive events - swirling transition region jets
In this paper, we extend our earlier work to provide additional evidence for
an alternative scenario to explain the nature of so-called `explosive events'.
The bi-directed, fast Doppler motion of explosive events observed
spectroscopically in the transition region emission is classically interpreted
as a pair of bidirectional jets moving upward and downward from a reconnection
site. We discuss the problems of such a model. In our previous work, we focused
basically on the discrepancy of fast Doppler motion without detectable motion
in the image plane. We now suggest an alternative scenario for the explosive
events, based on our observations of spectral line tilts and bifurcated
structure in some events. Both features are indicative of rotational motion in
narrow structures. We explain the bifurcation as the result of rotation of
hollow cylindrical structures and demonstrate that such a sheath model can also
be applied to explain the nature of the puzzling `explosive events'. We find
that the spectral tilt, the lack of apparent motion, the bifurcation, and a
rapidly growing number of direct observations support an alternative scenario
of linear, spicular-sized jets with a strong spinning motion.Comment: 9 pages, 3 figures, accepted for publication in Solar Physic
How parents perceive and feel about participation in community activities: The comparison between parents of preschoolers with and without autism spectrum disorders
The present study compared how parents of preschoolers with and without Autism Spectrum Disorders (ASD) perceived and felt about participation in community activities. A questionnaire survey was conducted with 380 Hong Kong parents of preschoolers with ASD and 214 Hong Kong parents of preschoolers without ASD. The two groups were not different in their willingness and frequency of participation in community activities. However, the psychological processes underneath their willingness were very different. Among the parents of preschoolers with ASD, their willingness was associated with how they perceived the difficulty and importance of the participation and what emotions they experienced during the activities. This pattern of association was not evident among the parents of preschoolers without ASD. Copyright © The Author(s), 2010.published_or_final_versio
A framework for the local information dynamics of distributed computation in complex systems
The nature of distributed computation has often been described in terms of
the component operations of universal computation: information storage,
transfer and modification. We review the first complete framework that
quantifies each of these individual information dynamics on a local scale
within a system, and describes the manner in which they interact to create
non-trivial computation where "the whole is greater than the sum of the parts".
We describe the application of the framework to cellular automata, a simple yet
powerful model of distributed computation. This is an important application,
because the framework is the first to provide quantitative evidence for several
important conjectures about distributed computation in cellular automata: that
blinkers embody information storage, particles are information transfer agents,
and particle collisions are information modification events. The framework is
also shown to contrast the computations conducted by several well-known
cellular automata, highlighting the importance of information coherence in
complex computation. The results reviewed here provide important quantitative
insights into the fundamental nature of distributed computation and the
dynamics of complex systems, as well as impetus for the framework to be applied
to the analysis and design of other systems.Comment: 44 pages, 8 figure
Erasmus Language students in a British University – a case study
Students’ assessment of their academic experience is actively sought by Higher Education institutions, as evidenced in the National Student Survey introduced in 2005. Erasmus students, despite their growing numbers, tend to be excluded from these satisfaction surveys, even though they, too, are primary customers of a University. This study aims to present results from bespoke questionnaires and semi-structured interviews with a sample of Erasmus students studying languages in a British University. These methods allow us insight into the experience of these students and their assessment as a primary customer, with a focus on language learning and teaching, university facilities and student support. It investigates to what extent these factors influence their levels of satisfaction and what costs of adaptation if any, they encounter. Although excellent levels of satisfaction were found, some costs affect their experience. They relate to difficulties in adapting to a learning methodology based on a low number of hours and independent learning and to a guidance and support system seen as too stifling. The results portray this cohort’s British University as a well-equipped and well-meaning but ultimately overbearing institution, which may indicate that minimising costs can eliminate some sources of dissatisfaction
Long-term evolution of orbits about a precessing oblate planet. 3. A semianalytical and a purely numerical approach
Construction of a theory of orbits about a precessing oblate planet, in terms
of osculating elements defined in a frame of the equator of date, was started
in Efroimsky and Goldreich (2004) and Efroimsky (2005, 2006). We now combine
that analytical machinery with numerics. The resulting semianalytical theory is
then applied to Deimos over long time scales. In parallel, we carry out a
purely numerical integration in an inertial Cartesian frame. The results agree
to within a small margin, for over 10 Myr, demonstrating the applicability of
our semianalytical model over long timescales. This will enable us to employ it
at the further steps of the project, enriching the model with the tides, the
pull of the Sun, and the planet's triaxiality. Another goal of our work was to
check if the equinoctial precession predicted for a rigid Mars could have been
sufficient to repel the orbits away from the equator. We show that for low
initial inclinations, the orbit inclination reckoned from the precessing
equator of date is subject only to small variations. This is an extension, to
non-uniform precession given by the Colombo model, of an old result obtained by
Goldreich (1965) for the case of uniform precession and a low initial
inclination. However, near-polar initial inclinations may exhibit considerable
variations for up to +/- 10 deg in magnitude. Nevertheless, the analysis
confirms that an oblate planet can, indeed, afford large variations of the
equinoctial precession over hundreds of millions of years, without repelling
its near-equatorial satellites away from the equator of date: the satellite
inclination oscillates but does not show a secular increase. Nor does it show
secular decrease, a fact that is relevant to the discussion of the possibility
of high-inclination capture of Phobos and Deimos
Output Stability and Semilinear Sets in Chemical Reaction Networks and Deciders
Abstract. We study the set of output stable configurations of chemical reaction deciders (CRDs). It turns out that CRDs with only bimolecular reactions (which are almost equivalent to population protocols) have a special structure that allows for an algorithm to efficiently calculate the (finite) set of minimal output stable configurations. As a consequence, a relatively large sequence of configurations may be efficiently checked for output stability. We also provide a number of observations regarding the semilinearity result of Angluin et al. [Distrib. Comput., 2007] from the context of population protocols (which is a central result for output stable CRDs). In particular, we observe that the computation-friendly class of totally stable CRDs has equal expressive power as the larger class of output stable CRDs.
Detector Description and Performance for the First Coincidence Observations between LIGO and GEO
For 17 days in August and September 2002, the LIGO and GEO interferometer
gravitational wave detectors were operated in coincidence to produce their
first data for scientific analysis. Although the detectors were still far from
their design sensitivity levels, the data can be used to place better upper
limits on the flux of gravitational waves incident on the earth than previous
direct measurements. This paper describes the instruments and the data in some
detail, as a companion to analysis papers based on the first data.Comment: 41 pages, 9 figures 17 Sept 03: author list amended, minor editorial
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