21,838 research outputs found
The end of the map?
Martin Smith and Andy Howard* explain why moving away from the printed map to a digital 3D National Geological Model is a ‘coming of age’ for William Smith’s great visio
Bayesian Modelling of Direct and Indirect Effects of Marine Reserves on Fishes : A thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Statistics at Massey University, Albany, New Zealand.
This thesis reviews and develops modern advanced statistical methodology for
sampling and modelling count data from marine ecological studies, with specific applications
to quantifying potential direct and indirect effects of marine reserves on fishes in north
eastern New Zealand. Counts of snapper (Pagrus auratus: Sparidae) from baited underwater
video surveys from an unbalanced, multi-year, hierarchical sampling programme were
analysed using a Bayesian Generalised Linear Mixed Model (GLMM) approach, which
allowed the integer counts to be explicitly modelled while incorporating multiple fixed and
random effects. Overdispersion was modelled using a zero-inflated negative-binomial error
distribution. A parsimonious method for zero inflation was developed, where the mean of the
count distribution is explicitly linked to the probability of an excess zero. Comparisons of
variance components identified marine reserve status as the greatest source of variation in
counts of snapper above the legal size limit. Relative densities inside reserves were, on
average, 13-times greater than outside reserves.
Small benthic reef fishes inside and outside the same three reserves were surveyed to
evaluate evidence for potential indirect effects of marine reserves via restored populations of
fishery-targeted predators such as snapper. Sites for sampling were obtained randomly from
populations of interest using spatial data and geo-referencing tools in R—a rarely used
approach that is recommended here more generally to improve field-based ecological
surveys. Resultant multispecies count data were analysed with multivariate GLMMs
implemented in the R package MCMCglmm, based on a multivariate Poisson lognormal error
distribution. Posterior distributions for hypothesised effects of interest were calculated
directly for each species. While reserves did not appear to affect densities of small fishes,
reserve-habitat interactions indicated that some endemic species of triplefin (Tripterygiidae)
had different associations with small-scale habitat gradients inside vs outside reserves. These patterns were consistent with a behavioural risk effect, where small fishes may be more
strongly attracted to refuge habitats to avoid predators inside vs outside reserves.
The approaches developed and implemented in this thesis respond to some of the
major current statistical and logistic challenges inherent in the analysis of counts of
organisms. This work provides useful exemplar pathways for rigorous study design,
modelling and inference in ecological systems
Dust emission from Barnard 35: Gas heating anomaly resolved
The molecular cloud B35 has puzzled observers because it contains gas which is, at T sub g approx. = 23 K, hotter that the surrounding dust whose T sub d approx. = 10 K. An investigation of the IRAS data, however, shows a previously unreported dust component at T sub d approx. 33 K, whose luminosity is ample to heat the gas. IRAS also finds that about 12 percent of the total luminosity around the core, and about 20 percent along the rim, arises from the small grain component with T less than or = 300 K. The temperature of these two components vary across the source, and this behavior is discussed. The results illustrate the presence of multiple components of dust in these clouds, and emphasize the need for data at multiple wavelengths
The strengthening of certain stainless steels by the reverse martensite transformation
Imperial Users onl
Irrelevant Exceptional Divisors for Curves on a Smooth Surface
Given a singular curve on a smooth surface, we determine which exceptional
divisors on the minimal resolution of that curve contribute toward its jumping
numbers.Comment: Added reference to Favre & Jonsson and a slight extension of the
comment immediately following Definition 2.
An Entry Point for Formal Methods: Specification and Analysis of Event Logs
Formal specification languages have long languished, due to the grave
scalability problems faced by complete verification methods. Runtime
verification promises to use formal specifications to automate part of the more
scalable art of testing, but has not been widely applied to real systems, and
often falters due to the cost and complexity of instrumentation for online
monitoring. In this paper we discuss work in progress to apply an event-based
specification system to the logging mechanism of the Mars Science Laboratory
mission at JPL. By focusing on log analysis, we exploit the "instrumentation"
already implemented and required for communicating with the spacecraft. We
argue that this work both shows a practical method for using formal
specifications in testing and opens interesting research avenues, including a
challenging specification learning problem
Selection and static calibration of the Marsh J1678 pressure gauge
During the experimental testing of the ultralight, it was determined that a pressure gauge would be required to monitor the simulated flight loads. After analyzing several factors, which are indicated in the discussion section of this report, the Marsh J1678 pressure gauge appeared to be the prominent candidate for the task. However, prior to the final selection, the Marsh pressure gauge was calibrated twice by two different techniques. As a result of the calibration, the Marsh gauge was selected as the appropriate measuring device during the structural testing of the ultralight. Although, there are commerical pressure gauges available on the market that would have proven to be more efficient and accurate. However, in order to obtain these characteristics in a gauge, one has to pay the price on the price tag, and this value is an exponential function of the degree of accuracy efficiency, precision, and many other features that may be designed into the gauge. After analyzing the extent of precision and accuracy that would be required, a more expensive gauge wouldn't have proven to be a financial benefit towards the outcome of the experiment
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