NUI Maynooth Eprint Archive
Not a member yet
18159 research outputs found
Sort by
Using a surface energy budget framework to characterize grass-biophysical response to changes in climate in support of on-farm decision making in Ireland
No full textxxiv
Abstract
This thesis, for the first time in Ireland, uses a framework that combines a land surface scheme
(LSS) based on a surface energy budget theory, available environmental observations, land
surface and atmospheric analyses, to understand essential mechanistic factors that
determine grass growth response across the Irish landscape. A soil moisture model parameter
(C soil)
is identified as the key factor that distinguishes soil types and their ability to retain
water for plant growth, plant response to exchange processes, and drives the response of LSS
in drying soils. A Modification of this parameter indicates that the LSS can be transferred to
other locations. In the context of understanding the links between land surface dynamic
processes and the persistence of 2018 summer drought regionally, drying soils and high
atmospheric anomalies result in a reduced evapotranspiration (ET) process. This is the
situation over grasslands in the east and south east of the country where a wet ‘evaporative’
regime quickly shifts into a ‘transitional’ regime in which vegetation functioning and ET are
controlled by soil water availability. Particularly, a threshold value of soil moisture content
that suggests the onset of 2018 agricultural drought has been found across the regions. The
importance of water use efficiency for monitoring grass growth at field level and for
distinguishing zones of optimum productivity is further discussed in the thesis. Overall, the
findings demonstrate the potential consequences of climate change on Irish grasslands and
the need for policies that are tailored to reinforcing observation networks to complement
theories and model outputs akin to on-farm adaptation and optimization of water availability
and productivity
Wave-to-grid (W2G) control of a wave energy converter
No full textGrid integration of wave energy involves various power train stages from device to grid, such as a power take-off
stage, a power conversion stage, and a power conditioning stage. The coupled performance of the complete
wave-to-grid system depends heavily on the dynamics of each stage and their respective controllers. However,
the control objectives of various stages may not align with each other and pose a potential problem, in terms of
economic performance and grid integration. This study presents a complete wave-to-grid control approach for a
wave energy converter, ensuring that the system performs optimally under variable wave resource conditions.
The proposed system comprises a point absorber wave energy converter oscillating in heave, a linear permanent
magnet generator, and back-to-back power converters for connection to the grid. Additionally, short term energy
storage, based on an ultra-capacitor, is also added to the DC link between the back-to-back converters for power
quality improvement. In the paper, a mathematical model is derived for the individual components of the waveto-grid system. Then, the controllers for each stage of the power train are designed. A LiTe-Con controller is used
for maximum power extraction on the device side, while Lyapunov-based nonlinear controllers are designed for
power converter control in order to achieve the full range of control objectives. The result shows that the proposed controllers accomplish the desired control objectives and perform well under various operating conditions
The Complex and Changing Face of Higher Education Language Teaching in the Republic of Ireland.
No full textThe landscape of language learning and teaching in higher education (HE) in Ireland is complex and varied. Between institutions, a diversity of organisational structures are
identifiable and, even within institutions, it can be seen that the provision of language education can vary significantly. In this paper, we present an overview of complexity within language education in Irish higher education which we investigated as part of
our scoping exercise for the Higher Education Language Educator Competences (HELECs) project. In order to manage this complexity, we have taken a number of
different approaches to gathering and analysing relevant data. Firstly, we attempt to ascertain which languages are offered and the programmes within which they are
available. We rely here on data gathered by Post-Primary Languages Ireland (PPLI) and published on the Careers Portal website. Secondly, we present an analysis of the
structure of language provision units within Universities and Institutes of Technology (IoTs). These data are publicly available through the institutions’ websites. Thirdly, we
provide a detailed examination of the complex constellation of staff profiles involved in language education at four institutions representing the categories of higher education
institutions (HEIs) in the system. We interrogate language units’ websites to obtain this information and augment it with data gathered through the HELECs project. In
presenting these data, we aim to provide an overview of the landscape of language teaching and learning in HE in Ireland. In conducting this data analysis, we identify
areas of concern for the sector including: the visibility of languages within HEIs; the multiplicity of professional identities of those who teach language in HE; and issues of
precarity of employment and career progression in HE language education
Understanding the cost of care of type 2 diabetes mellitus - a value measurement perspective
No full textObjectives:
We explore the cost of care of type 2 diabetes mellitus (T2DM) using time-driven activity-based costing (TDABC) and connect that cost to resulting patient health outcomes.
Design:
We construct six care pathways varying from low-risk to high-risk patients over a 12-month cycle of care. We collect time, resource and cost data on activities in each care pathway and compute a time-driven estimate of cost. Use of patient outcome data highlights the health outcomes achieved.
Setting:
Primary, secondary and tertiary care.
Participants:
Medical staff involved in the care of patients with T2DM.
Primary and secondary measures:
Primary: resources consumed to provide T2DM care. Secondary: health outcomes for representative patient within each patient category.
Results:
By computing cost of T2DM care and associated complications of chronic kidney disease, active foot disease, moderate risk of active foot disease and myocardial infarction, we show that when patients develop acute complications, significant costs are incurred, as compared with the cost of maintaining a patient at low or moderate risk. Variance analysis further informs decision making by showing the need to have the right personnel doing the right tasks at the right time to control costs.
Conclusions:
A TDABC approach facilitates an understanding of the drivers of cost in chronic illness care. Our paper highlights the stages in the care pathway where different settings, decision making and a more optimal use of resources could assist with achievement of better patient outcomes
An Investigation into Exchange Rate Dynamics, Adjustment Mechanisms and Monetary Policy
No full textExchange rate regimes have evolved substantially over the years, right from the Gold Standard
to the Bretton Woods era and post-Bretton Woods periods. The post-Bretton Woods era has
seen the emergence of currency unions and a whole range of hybrid and sophisticated
exchange rate regimes. This study attempts to recover the preferred anchor currencies of
different countries and further uses a Markov-switching process to decompose exchange rate
behaviour into component regimes. The regression-based results reveal the preferred anchor
currencies while the Markov-switching results indicate that the model is able to decompose the
currency behaviour of eight currencies into appreciating and depreciating regimes.
Furthermore, the Markov results identify the key turning points in the exchange rate series,
especially the 2008/2009 crisis period
Optimal control of pitch and rotational velocity for a cyclorotor wave energy device
No full textThe development of optimal control strategies for cyclorotor wave energy converters (WECs) is at an early stage. In this paper, we present new methods and solutions for optimal pitch and/or rotational velocity control strategies for different configurations of cyclorotor-based WECs, in both monochromatic and panchromatic waves. The cyclorotor is modelled with the use of an approximate two-dimensional mathematical model, where hydrofoils are approximated as point source vortices in potential waves. The goal of the developed control strategy is to determine the optimal velocity profile, and/or pitch angle variations, for maximum energy conversion, in terms of generated shaft power. The solutions, obtained with the use of spectral methods, show a clear benefit in using a variable velocity for cyclorotors with either one or two hydrofoils, in monochromatic waves, while the real time pitching did not significantly increase the value of the absorbed wave energy. We also present control results for panchromatic waves, assuming all the properties of incoming wave packages are known. The obtained solutions have shown significant benefit in joint optimal pitch and velocity control, especially in the case of panchromatic waves
Extensions to Bayesian tree-based machine learning algorithms
No full textBayesian additive regression trees (BART) is a Bayesian tree-based algorithm
which can provide high predictive accuracy in both classification and regression
problems. Unlike other machine learning algorithms based on an ensemble of trees,
such as random forests and gradient boosting, BART is not based on recursive partitioning.
Rather, it is a fully Bayesian model built upon a likelihood function and
diligently specified prior distributions.
In this thesis, we propose methodological extensions to BART to deal with two
main limitations of tree-based methods: the limited ability to fit smooth functions,
which is inherently associated with how methods based on trees are built, as well
as the lack of adequate mechanisms that enable to quantify in an interpretable
fashion the impact of certain inputs of primary interest on the output.
Firstly, we present an extension that aims to deal with linear effects at the terminal
nodes level. By considering linear piecewise functions instead of piecewise constants,
local linearities are captured more efficiently and fewer trees are required to
achieve equal or better performance than BART. Secondly, motivated by an agricultural
application, we develop a semi-parametric BART model in which marginal
genotypes and environment effects are estimated along with their interactions.
Last, motivated by data collected in 2019 under the seventh cycle of the quadrennial
Trends in International Mathematics and Science Study, we extend semiparametric
models based on BART, which generally assume that the set of covariates
in the linear predictor and the BART model are mutually exclusive, to account
for shared covariates. In particular, we change the tree-generation moves in BART
to deal with bias/confounding between the parametric and non-parametric components,
even when they have covariates in common
QUBIC I: Overview and science program
No full textThe Q & U Bolometric Interferometer for Cosmology (QUBIC) is a novel kind
of polarimeter optimized for the measurement of the B-mode polarization of the Cosmic Microwave Background (CMB), which is one of the major challenges of observational cosmology.
The signal is expected to be of the order of a few tens of nK, prone to instrumental systematic effects and polluted by various astrophysical foregrounds which can only be controlled
through multichroic observations. QUBIC is designed to address these observational issues
with a novel approach that combines the advantages of interferometry in terms of control
of instrumental systematic effects with those of bolometric detectors in terms of wide-band,
background-limited sensitivity. The QUBIC synthesized beam has a frequency-dependent
shape that results in the ability to produce maps of the CMB polarization in multiple subbands within the two physical bands of the instrument (150 and 220 GHz). These features
make QUBIC complementary to other instruments and makes it particularly well suited to
characterize and remove Galactic foreground contamination. In this article, first of a series of
eight, we give an overview of the QUBIC instrument design, the main results of the calibration
campaign, and present the scientific program of QUBIC including not only the measurement
of primordial B-modes, but also the measurement of Galactic foregrounds. We give forecasts for typical observations and measurements: with three years of integration on the sky and
assuming perfect foreground removal as well as stable atmospheric conditions from our site in
Argentina, our simulations show that we can achieve a statistical sensitivity to the effective
tensor-to-scalar ratio (including primordial and foreground B-modes) σ(r) = 0.015
Impact of CO2 emission taxation and fuel types on Arctic shipping attractiveness
No full textThis study investigates the impact of hubs, CO2 emission taxation policy, and bunker fuels on the economic and environmental attractiveness of the Northern Sea Route (NSR).
Twenty-eight years of historical ice data have been combined to define the uncertainty level of ice thickness and concentration and converted to risk indexes using POLARIS, a risk management tool. The shortest travel times have been defined using the risk levels and a time-dependent shortest path algorithm.
The results stress that the carbon tax is not antinomic with profit. Moreover, the use of hubs was not found to be economically advantageous for a majority of the examined scenarios. Furthermore, although it increases the overall emissions, this reduces the CO2 emissions per container due to the rise in the shipping volumes. Demand elasticity to transit time and to freight rates shows that the choice of hubs significantly impacts the NSR’s economic and environmental attractiveness
Special Issue: Design, management, sustainability and evaluation of transportation systems in the Arctic
No full textThe abstract is included in the text