35 research outputs found
5th anniversary focus: author Peter Fretwell on penguins and climate change
No full textPeter Fretwell is a senior scientist in the Mapping and Geographic Information Centre, at the British Antarctic Survey
5th anniversary focus: author Peter Fretwell on penguins and climate change
No full textPeter Fretwell is a senior scientist in the Mapping and Geographic Information Centre, at the British Antarctic Survey.
Peter has pioneered the use of satellite imagery to study polar wildlife such as penguins, walrus, whales, and seabirds; and has authored books on penguins and Antarctic environments
Correction : Using remote sensing to detect whale strandings in remote areas: The case of sei whales mass mortality in Chilean Patagonia(PLoS ONE (2019) 14:10(e0222498)DOI:10.1371/journal.pone.0222498)
No full textPublisher Copyright: © 2019 Fretwell et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.In the funding statement, the description of funding awarded to Maria Jose Perez-Alvarez is incomplete. The correct information is as follows: Maria Jose Perez-Alvarez was funded by CONICYT-FONDECYT Initiation Program 11170182, Postdoctoral FONDECYT Program 3140513, Projects ICM P05-002 and PFB 023
Quantifying the causes and consequences of variation in satellite-derived population indices: a case study of emperor penguins
No full text© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Labrousse, S., Iles, D., Viollat, L., Fretwell, P., Trathan, P. N., Zitterbart, D. P., Jenouvrier, S., & LaRue, M. Quantifying the causes and consequences of variation in satellite-derived population indices: a case study of emperor penguins. Remote Sensing in Ecology and Conservation, (2021), https://doi.org/10.1002/rse2.233.Very high-resolution satellite (VHR) imagery is a promising tool for estimating the abundance of wildlife populations, especially in remote regions where traditional surveys are limited by logistical challenges. Emperor penguins Aptenodytes forsteri were the first species to have a circumpolar population estimate derived via VHR imagery. Here we address an untested assumption from Fretwell et al. (2012) that a single image of an emperor penguin colony is a reasonable representation of the colony for the year the image was taken. We evaluated satellite-related and environmental variables that might influence the calculated area of penguin pixels to reduce uncertainties in satellite-based estimates of emperor penguin populations in the future. We focused our analysis on multiple VHR images from three representative colonies: Atka Bay, Stancomb-Wills (Weddell Sea sector) and Coulman Island (Ross Sea sector) between September and December during 2011. We replicated methods in Fretwell et al. (2012), which included using supervised classification tools in ArcGIS 10.7 software to calculate area occupied by penguins (hereafter referred to as ‘population indices’) in each image. We found that population indices varied from 2 to nearly 6-fold, suggesting that penguin pixel areas calculated from a single image may not provide a complete understanding of colony size for that year. Thus, we further highlight the important roles of: (i) sun azimuth and elevation through image resolution and (ii) penguin patchiness (aggregated vs. distributed) on the calculated areas. We found an effect of wind and temperature on penguin patchiness. Despite intra-seasonal variability in population indices, simulations indicate that reliable, robust population trends are possible by including satellite-related and environmental covariates and aggregating indices across time and space. Our work provides additional parameters that should be included in future models of population size for emperor penguins.Geospatial support for this work was provided by the Polar Geospatial Center under NSF-OPP awards 1043681 and 1559691. NCAR- PPC visitor funds and Ian Nisbet that supported the internship of LV. WWF-UK supported PNT and PTF under grant GB095701. DZ was supported by The Penzance Endowed Fund and The Grayce B. Kerr Fund in Support of Assistant Scientists. To SJ, ML, SL, LV, NSF OPP 1744794
The relationship between teachers' perceptions of the school learning climate, students' reading and math achievement levels, and the high school dropout rate in the Atlanta public schools, 1989
No full textThe purpose of this correlational study was to determine the relationship between teachers' perceptions of selected school learning climate variables, students' reading and math achievement levels, and the high school dropout rate in the Atlanta Public Schools. The school learning climate variables were those identified in A School Learning Climate Assessment Instrument. The original validation for this instrument was in elementary schools. Validation at the secondary level was obtained for this study. The following variables were found to have a significant relationship to the high school dropout rate in the Atlanta Public Schools: Emphasis on Achievement; Teacher Expectations of Students; Evaluation of the Instructional Program; Safe and Orderly Environment; Time Devoted to Instruction; and Reading Achievement. Further investigation revealed Teacher Expectations of Students as the strongest predictor and Emphasis on Achievement as the second strongest predictor of dropping out in the Atlanta Public Schools. The major implications and recommendations from the study are as follows: Implications: 1. Raising teachers expectations of student performance will lead to a decrease in the dropout rate. 2. Implementing strategies to improve students' reading abilities will lead to a decrease in the dropout rate. Recommendations: 1. Implement a school climate improvement program. 2. Provide staff development activities that focus on increasing teachers' expectations of students
Performance Modelling and Analysis of Weighted Fair Queueing for Scheduling in Communication Networks. An investigation into the Development of New Scheduling Algorithms for Weighted Fair Queueing System with Finite Buffer.
No full textAnalytical modelling and characterization of Weighted Fair Queueing (WFQ) have recently
received considerable attention by several researches since WFQ offers the minimum
delay and optimal fairness guarantee. However, all previous work on WFQ has
focused on developing approximations of the scheduler with an infinite buffer because of
supposed scalability problems in the WFQ computation.
The main aims of this thesis are to study WFQ system, by providing an analytical WFQ
model which is a theoretical construct based on a form of processor sharing for finite
capacity. Furthermore, the solutions for classes with Poisson arrivals and exponential
service are derived and verified against global balance solution.
This thesis shows that the analytical models proposed can give very good results under
particular conditions which are very close to WFQ algorithms, where accuracy of
the models is verified by simulations of WFQ model. Simulations were performed with
QNAP-2 simulator. In addition, the thesis presents several performance studies signifying
the power of the proposed analytical model in providing an accurate delay bounds to
a large number of classes.
These results are not able to cover all unsolved issues in the WFQ system. They represent
a starting point for the research activities that the Author will conduct in the future. The
author believes that the most promising research activities exist in the scheduler method
to provide statistical guarantees to multi-class services. The author is convinced that
alternative software, for example, on the three class model buffer case, is able to satisfy
the large number of buffer because of the software limitation in this thesis. While they can
be a good topic for long-term research, the short-medium term will show an increasing
interest in the modification of the WFQ models to provide differentiated services.Ministry of Higher Educatio
Functionals of exponential Brownian motion and divided differences
No full textWe provide a surprising new application of classical approximation theory to a fundamental asset-pricing model of mathematical finance. Specifically, we calculate an analytic value for the correlation coefficient between
exponential Brownian motion and its time average, and we find the use of divided differences greatly elucidates formulae, providing a path to several new results. As applications, we find that this correlation coefficient is always at least 1/p2 and, via the Hermite–Genocchi integral relation, demonstrate that all moments of the time average are certain divided differences of the exponential function. We also prove that these moments agree with the somewhat more complex formulae obtained by Oshanin and Yor
Performance modelling and analysis of weighted fair queueing for scheduling in communication networks : an investigation into the development of new scheduling algorithms for weighted fair queueing system with finite buffer
No full textAnalytical modelling and characterization of Weighted Fair Queueing (WFQ) have recently received considerable attention by several researches since WFQ offers the minimum delay and optimal fairness guarantee. However, all previous work on WFQ has focused on developing approximations of the scheduler with an infinite buffer because of supposed scalability problems in the WFQ computation. The main aims of this thesis are to study WFQ system, by providing an analytical WFQ model which is a theoretical construct based on a form of processor sharing for finite capacity. Furthermore, the solutions for classes with Poisson arrivals and exponential service are derived and verified against global balance solution. This thesis shows that the analytical models proposed can give very good results under particular conditions which are very close to WFQ algorithms, where accuracy of the models is verified by simulations of WFQ model. Simulations were performed with QNAP-2 simulator. In addition, the thesis presents several performance studies signifying the power of the proposed analytical model in providing an accurate delay bounds to a large number of classes. These results are not able to cover all unsolved issues in the WFQ system. They represent a starting point for the research activities that the Author will conduct in the future. The author believes that the most promising research activities exist in the scheduler method to provide statistical guarantees to multi-class services. The author is convinced that alternative software, for example, on the three class model buffer case, is able to satisfy the large number of buffer because of the software limitation in this thesis. While they can be a good topic for long-term research, the short-medium term will show an increasing interest in the modification of the WFQ models to provide differentiated services.EThOS - Electronic Theses Online ServiceMinistry of Higher EducationGBUnited Kingdo
Achieving selenium load targets
No full textPresented at Contemporary challenges for irrigation and drainage: proceedings from the USCID 14th technical conference on irrigation, drainage and flood control held on June 3-6, 1998 in Phoenix, Arizona.Seven irrigation and drainage districts in the California's San Joaquin Valley are participating in a regional program to reduce the load of selenium entering the San Joaquin River. Farmers have improved their irrigation methods to reduce surface runoff and deep percolation, district staff have improved their operations to support farm-level water management efforts, and a regional association has been formed to operate regional drainage facilities and coordinate efforts to achieve monthly and annual selenium load targets. The costs of these efforts include farm-level expenditures for new irrigation systems and for increases in irrigation labor and other water management inputs, district-level expenditures for new facilities and staff to manage water deliveries and drainage water reduction efforts more aggressively, and the fixed and variable costs of operating and maintaining regional drainage facilities. Empirical estimates of these costs for the Broadview Water District in 1997 include 11 per acre for district-level efforts, and $14 per acre for supporting regional drainage activities
Using and evaluating CASE tools : from software engineering to phenomenology
No full textCASE (Computer-Aided Systems Engineering) is a recent addition to the long line of
"silver bullets" that promise to transform information systems development, delivering
new levels of quality and productivity. CASE is particularly intriguing because
information systems (IS) practitioners spend their working lives applying information
technology (IT) to other people's work, and now they are applying it to themselves.
CASE research to date has been dominated by accounts of tool development,
normative writings (for example practitioner success stories) and surveys recording
IT specialists' perceptions. There have been very few in-depth studies of tool use,
and very few attempts to quantify benefits, therefore the essence of the CASE process
remains largely unexplored, and the views of stakeholders other than the IT specialists
have yet to be heard.
The research presented here addresses these concerns by adopting a hybrid research
approach combining action research, grounded theory and phenoinenology and using
both qualitative and quantitative data in order to tell the story of a system developer's
experience in using CASE tools in three information systems projects for a major UK
car manufacturer over a four year period. The author was the lead developer on all
three projects. Action research is a learning process, the researcher is an explorer.
At the start of this project it was assumed that the tools would be the focus of the
work. As the research progressed it became evident that the tools were but part of
a richer organisational context in which culture, politics, history, external initiatives
and cognitive limitations played important roles. The author continued to record
experiences and impressions of tool use in the project diary together with quality and
productivity metrics. But the diary also became home to a story of organisational
developments that had not originally been foreseen.
The principal contribution made by the work is to identity the narrow positivistic
nature of CASE knowledge, and to show via the research stories the overwhelming
importance of organisational context to systems development success and how the
exploration of context is poorly supported by the tools. Sixteen further contributions
are listed in the Conclusions to the thesis, including a major extension to Wynekoop
and Conger's CASE research taxonomy, an identification of the potentially
misleading nature of quantitative IS assessment and further evidence of the limitations
of the "scientific" approach to systems development.
The thesis is completed by two proposals for further work. The first seeks to
advance IS theory by developing further a number of emerging process models of IS
development. The second seeks to advance IS practice by asking the question "How
can CASE tools be used to stimulate awareness and debate about the effects of
organisational context?", and outlines a programme of research in this area
