721 research outputs found
From coinductive proofs to exact real arithmetic: theory and applications
Based on a new coinductive characterization of continuous functions we
extract certified programs for exact real number computation from constructive
proofs. The extracted programs construct and combine exact real number
algorithms with respect to the binary signed digit representation of real
numbers. The data type corresponding to the coinductive definition of
continuous functions consists of finitely branching non-wellfounded trees
describing when the algorithm writes and reads digits. We discuss several
examples including the extraction of programs for polynomials up to degree two
and the definite integral of continuous maps
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Managing climate risk in water supply systems : materials and tools designed to empower technical professionals to better understand key issues
This manual has been developed as a learning tool to be used with a
companion series of practical exercises. They have been developed to
provide a hands-on approach to learning key concepts in hydrology and
climate science as they relate to climate risk management in water supply
systems, as introduced in the text
Microscale distribution patterns of terrestrial bryophytes in a subalpine forest: the use of logistic regression as an interpretive tool
This study investigated microhabitat relationships of terrestrial bryophytes in a subalpine forest of coastal British Columbia. Substratum affinities were characterized for dominant bryophytes. Logistic regression analysis was used to gain insight into the ecological determinants of fine scale (0.1 m2) bryophyte distribution by examining the predictive relationship between bryophyte species occurrence and localized environmental conditions, as well as the coverage of other bryophytes. The predictive relationships were compared to evaluate the relative importance of environmental factors versus interspecific interactions in structuring bryophyte communities. The results indicate that bryophytes show unique responses in their relationships to environmental conditions and other bryophytes. Positive feedback appears to be an important process among terrestrial bryophytes in subalpine forests
Egg shape in the Common Guillemot Uria aalge and Brunnich’s Guillemot U. lomvia: not a rolling matter?
The adaptive significance of avian egg shape is
poorly understood, and has been studied only in those
species producing pyriform (pear-shaped, or pointed) eggs:
waders and guillemots (murres) Uria spp., albeit to a
limited extent. In the latter, it is widely believed that the
pyriform shape has evolved to minimise their likelihood of
rolling off a cliff ledge: the idea being that the more
pointed the egg, the narrower the arc in which it rolls, and
the less likely it is it will fall from a cliff ledge. Previous
research also claimed that the rolling trajectory—the
diameter of the arc they describe—of Common Guillemot
U. aalge eggs is influenced not only by its shape but also
by its mass, with heavier (i.e. larger) eggs describing a
wider arc than lighter eggs. The finding that both shape and
mass determined the rolling trajectory of Common
Guillemot eggs (the shape–mass hypothesis) was used to
explain the apparent anomaly that Bru¨nnich’s Guillemot U.
lomvia produce eggs that are less pointed, yet breed on
narrower ledges than Common Guillemots. They are able
to do this, it was suggested, because Bru¨nnich’s Guillemot
eggs are smaller and lighter in mass than those of Common
Guillemots. However, since some populations of
Bru¨nnich’s Guillemots produce eggs that are as large or
larger than those of some Common Guillemot populations,
the shape–mass hypothesis predicts that that (1) larger (i.e.
heavier) eggs of both guillemot species will be more
pyriform (pointed) in shape, and (2) that eggs of the two
species of same mass should be similarly pointed. We
tested these predictions and found: (1) only a weak, positive
association between egg volume and pointedness in
both guillemot species (\3% of the variation in egg shape
explained by egg volume), and (2) no evidence that eggs of
the two species of similar mass were more similar in shape:
regardless of their mass, Brunnich’s Guillemot eggs were
less pointed than Common Guillemot eggs. Overall, our
results call into question the long-held belief that protection
from rolling is the main selective factor driving guillemot
egg shape
OA06-06 LB. Evidence of vaccine-induced changes in breakthrough HIV-1 strains from the Step trial
Limits to Poisson's ratio in isotropic materials - general result for arbitrary deformation
The lower bound usually cited for Poisson's ratio {\nu} is -1, derived from
the relationship between {\nu} and the bulk and shear moduli. From
consideration of the longitudinal and biaxial moduli, we recently determined
that the lower bound on {\nu} for isotropic materials is actually 1/5, a value
also consistent with experimental measurements on real materials. Herein we
generalize this result, first by analyzing expressions for {\nu} in terms of
six common elastic constants, and then by considering arbitrary strains. The
results corroborate the prior finding that 1/5 <= {\nu} for linear elasticity
to be applicable.Comment: 15 pages, 3 figures, 1 tabl
Rethinking use-wear analysis and experimentation as applied to the study of past hominin tool use
In prehistoric human populations, technologies played a fundamental role in the acquisition of different resources and are represented in the main daily living activities, such as with bone, wooden, and stone-tipped spears for hunting, and chipped-stone tools for butchering.
Considering that paleoanthropologists and archeologists are focused on the study of different processes involved in the evolution of human behavior, investigating how hominins acted in the past through the study of evidence on archeological artifacts is crucial. Thus, investigat ing tool use is of major importance for a comprehensive understanding of all processes that characterize human choices of raw materials, techniques, and tool types. Many functional assumptions of tool use have been based on tool design and morphology according to archeologists’ interpretations and ethnographic observations. Such assumptions are used as
baselines when inferring human behavior and have driven an improvement in the methods and techniques employed in functional studies over the past few decades. Here, while arguing that use-wear analysis is a key discipline to assess past hominin tool use and to interpret the organization and variability of artifact types in the archeological record, we aim to review and discuss the current state-of-the-art methods, protocols, and their limitations. In doing so, our discussion focuses on three main topics: (1) the need for fundamental
improvements by adopting established methods and techniques from similar research fields, (2) the need to implement and combine different levels of experimentation, and (3) the crucial need to establish standards and protocols in order to improve data quality, standard ization, repeatability, and reproducibility. By adopting this perspective, we believe that studies will increase the reliability and applicability of use-wear methods on tool function.
The need for a holistic approach that combines not only use-wear traces but also tool technology, design, curation, durability, and efficiency is also debated and revised. Such a revision is a crucial step if archeologists want to build major inferences on human decision making behavior and biocultural evolution processes.info:eu-repo/semantics/publishedVersio
Do Lions Panthera leo Actively Select Prey or Do Prey Preferences Simply Reflect Chance Responses via Evolutionary Adaptations to Optimal Foraging?
Research on coursing predators has revealed that actions throughout the predatory behavioral sequence (using encounter rate, hunting rate, and kill rate as proxy measures of decisions) drive observed prey preferences. We tested whether similar actions drive the observed prey preferences of a stalking predator, the African lion Panthera leo. We conducted two 96 hour, continuous follows of lions in Addo Elephant National Park seasonally from December 2003 until November 2005 (16 follows), and compared prey encounter rate with prey abundance, hunt rate with prey encounter rate, and kill rate with prey hunt rate for the major prey species in Addo using Jacobs' electivity index. We found that lions encountered preferred prey species far more frequently than expected based on their abundance, and they hunted these species more frequently than expected based on this higher encounter rate. Lions responded variably to non-preferred and avoided prey species throughout the predatory sequence, although they hunted avoided prey far less frequently than expected based on the number of encounters of them. We conclude that actions of lions throughout the predatory behavioural sequence, but particularly early on, drive the prey preferences that have been documented for this species. Once a hunt is initiated, evolutionary adaptations to the predator-prey interactions drive hunting success
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