1,792 research outputs found
Laser photogrammetry reveals variation in growth and early survival in free-ranging bottlenose dolphins
Acknowledgements Many thanks to the Chicago Zoological Society team for their assistance during photo-identification surveys in Sarasota, Florida and the Scottish Marine Animal Stranding Scheme and University of North Carolina Wilmington Marine Mammal Stranding Program for providing measurements of stranded bottlenose dolphins. Thanks to Holly Fearnbach and Isla Graham for statistical advice, to Hera Sengers and all our fieldwork assistants for their fieldwork support and to four anonymous reviewers who kindly provided comments on the manuscript. Scottish Natural Heritage, Department of Energy and Climate Change, Beatrice Offshore Windfarm Ltd, Moray Offshore Renewables Ltd, Marine Scotland, The Crown Estate and Highlands and Islands Enterprise all provided funding for photo-identification surveys. Survey work was conducted under Scottish Natural Heritage Animal Scientific LicencesPeer reviewedPublisher PD
Nonparametric Markovian Learning of Triggering Kernels for Mutually Exciting and Mutually Inhibiting Multivariate Hawkes Processes
In this paper, we address the problem of fitting multivariate Hawkes
processes to potentially large-scale data in a setting where series of events
are not only mutually-exciting but can also exhibit inhibitive patterns. We
focus on nonparametric learning and propose a novel algorithm called MEMIP
(Markovian Estimation of Mutually Interacting Processes) that makes use of
polynomial approximation theory and self-concordant analysis in order to learn
both triggering kernels and base intensities of events. Moreover, considering
that N historical observations are available, the algorithm performs
log-likelihood maximization in operations, while the complexity of
non-Markovian methods is in . Numerical experiments on simulated
data, as well as real-world data, show that our method enjoys improved
prediction performance when compared to state-of-the art methods like MMEL and
exponential kernels
Combining Provenance Management and Schema Evolution
The combination of provenance management and schema evolution using the CHASE algorithm is the focus of our research in the area of research data management. The aim is to combine the construc- tion of a CHASE inverse mapping to calculate the minimal part of the original database — the minimal sub-database — with a CHASE-based schema mapping for schema evolution
Case-control study to detect protective factors on pig farms with low Salmonella prevalence
The prevalence of Salmonella in UK pigs is amongst the highest in Europe, highlighting the risk to public health and the need to investigate on-farm controls. The objective of this study was to identify factors currently in operation on pig farms that had maintained a low Salmonella seroprevalence. For this purpose a case-control study was designed and pig farms with a low (\u3c10%) seroprevalence were compared against two randomly selected control farms, sharing the same geographical region and production type. A total of 11,452 samples, including pooled and individual floor faeces and environmental samples from pigs and their vicinity were tested and prevalence examined. In addition, detailed questionnaires were completed during the farm visits to collect descriptive data for risk factor analysis. It was shown that control farms had significantly higher prevalence compared to the case farms (19.4% and 4.3% for pooled and 6.7% and 0.1% for individual samples, respectively). The two risk factor analyses identified multiple variables associated with Salmonella prevalence including variables related to feed, effectiveness of cleaning and disinfection, biosecurity and batch production
Bird wings act as a suspension system that rejects gusts
Musculoskeletal systems cope with many environmental perturbations without neurological control. These passive preflex responses aid animals to move swiftly through complex terrain. Whether preflexes play a substantial role in animal flight is uncertain. We investigated how birds cope with gusty environments and found that their wings can act as a suspension system, reducing the effects of vertical gusts by elevating rapidly about the shoulder. This preflex mechanism rejected the gust impulse through inertial effects, diminishing the predicted impulse to the torso and head by 32% over the first 80 ms, before aerodynamic mechanisms took effect. For each wing, the centre of aerodynamic loading aligns with the centre of percussion, consistent with enhancing passive inertial gust rejection. The reduced motion of the torso in demanding conditions simplifies crucial tasks, such as landing, prey capture and visual tracking. Implementing a similar preflex mechanism in future small-scale aircraft will help to mitigate the effects of gusts and turbulence without added computational burden
High aerodynamic lift from the tail reduces drag in gliding raptors
Many functions have been postulated for the aerodynamic role of the avian tail during steady-state flight. By analogy with conventional aircraft, the tail might provide passive pitch stability if it produced very low or negative lift. Alternatively, aeronautical principles might suggest strategies that allow the tail to reduce inviscid, induced drag: if the wings and tail act in different horizontal planes, they might benefit from biplane-like aerodynamics; if they act in the same plane, lift from the tail might compensate for lift lost over the fuselage (body), reducing induced drag with a more even downwash profile. However, textbook aeronautical principles should be applied with caution because birds have highly capable sensing and active control, presumably reducing the demand for passive aerodynamic stability, and, because of their small size and low flight speeds, operate at Reynolds numbers two orders of magnitude below those of light aircraft. Here, by tracking up to 20,000, 0.3 mm neutrally buoyant soap bubbles behind a gliding barn owl, tawny owl and goshawk, we found that downwash velocity due to the body/tail consistently exceeds that due to the wings. The downwash measured behind the centreline is quantitatively consistent with an alternative hypothesis: that of constant lift production per planform area, a requirement for minimizing viscous, profile drag. Gliding raptors use lift distributions that compromise both inviscid induced drag minimization and static pitch stability, instead adopting a strategy that reduces the viscous drag, which is of proportionately greater importance to lower Reynolds number fliers
A dependent nominal type theory
Nominal abstract syntax is an approach to representing names and binding
pioneered by Gabbay and Pitts. So far nominal techniques have mostly been
studied using classical logic or model theory, not type theory. Nominal
extensions to simple, dependent and ML-like polymorphic languages have been
studied, but decidability and normalization results have only been established
for simple nominal type theories. We present a LF-style dependent type theory
extended with name-abstraction types, prove soundness and decidability of
beta-eta-equivalence checking, discuss adequacy and canonical forms via an
example, and discuss extensions such as dependently-typed recursion and
induction principles
Quasi-ordered photonic structures colour the bluespotted ribbontail ray
Due to the scarcity of blue colour exhibited by natural organisms, highlighting the underlying this colour mechanisms is always very impactful for the understanding of the natural world. In this research, the colour of the blue rounded spots occurring in the skin of Taeniura lymma stingray was unveiled by a combination of experimental and numerical techniques. Our results demonstrated that this blue colour arises from coherent scattering in quasi-ordered photonic structures occurring in the skin of this stingray.</p
Quasi-ordered photonic structures colour the bluespotted ribbontail ray
Due to the scarcity of blue colour exhibited by natural organisms, highlighting the underlying this colour mechanisms is always very impactful for the understanding of the natural world. In this research, the colour of the blue rounded spots occurring in the skin of Taeniura lymma stingray was unveiled by a combination of experimental and numerical techniques. Our results demonstrated that this blue colour arises from coherent scattering in quasi-ordered photonic structures occurring in the skin of this stingray.</p
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Improving the condition number of estimated covariance matrices
High dimensional error covariance matrices and their inverses are used to weight the
contribution of observation and background information in data assimilation procedures. As
observation error covariance matrices are often obtained by sampling methods, estimates are
often degenerate or ill-conditioned, making it impossible to invert an observation error
covariance matrix without the use of techniques to reduce its condition number. In this paper
we present new theory for two existing methods that can be used to ‘recondition’ any covariance
matrix: ridge regression, and the minimum eigenvalue method. We compare these methods
with multiplicative variance inflation, which cannot alter the condition number of a matrix, but
is often used to account for neglected correlation information. We investigate the impact of
reconditioning on variances and correlations of a general covariance matrix in both a theoretical
and practical setting. Improved theoretical understanding provides guidance to users regarding
method selection, and choice of target condition number. The new theory shows that, for the
same target condition number, both methods increase variances compared to the original
matrix, with larger increases for ridge regression than the minimum eigenvalue method. We
prove that the ridge regression method strictly decreases the absolute value of off-diagonal
correlations. Theoretical comparison of the impact of reconditioning and multiplicative
variance inflation on the data assimilation objective function shows that variance inflation alters
information across all scales uniformly, whereas reconditioning has a larger effect on scales
corresponding to smaller eigenvalues. We then consider two examples: a general correlation
function, and an observation error covariance matrix arising from interchannel correlations. The
minimum eigenvalue method results in smaller overall changes to the correlation matrix than
ridge regression, but can increase off-diagonal correlations. Data assimilation experiments reveal
that reconditioning corrects spurious noise in the analysis but underestimates the true signal
compared to multiplicative variance inflation
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