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Memristor-based design solutions for mitigating parametric variations in IoT applications
Get PDFPhD ThesisRapid advancement of the internet of things (IoT) is predicated by two important factors
of the electronic technology, namely device size and energy-efficiency. With smaller
size comes the problem of process, voltage and temperature (PVT) variations of delays
which are the key operational parameters of devices. Parametric variability is also
an obstacle on the way to allowing devices to work in systems with unpredictable
power sources, such as those powered by energy-harvesters. Designers tackle these
problems holistically by developing new techniques such as asynchronous logic, where
mechanisms such as matching delays are widely used to adapt to delay variations. To
mitigate energy efficiency and power interruption issues the matching delays need to
be ideally retained in a non-volatile storage. Meanwhile, a resistive memory called
memristor becomes a promising component for power-restricted applications owing to
its inherent non-volatility. While providing non-volatility, the use of memristor in delay
matching incurs some power overheads. This creates the first challenge on the way of
introducing memristors into IoT devices for the delay matching.
Another important factor affecting the use of memristors in IoT devices is the
dependence of the memristor value on temperature. For example, a memristance
decoder used in the memristor-based components must be able to correct the read data
without incurring significant overheads on the overall system. This creates the second
challenge for overcoming the temperature effect in memristance decoding process.
In this research, we propose methods for improving PVT tolerance and energy
characteristics of IoT devices from the perspective of above two main challenges:
(i) utilising memristor to enhance the energy efficiency of the delay element (DE), and
(ii) improving the temperature awareness and energy robustness of the memristance
decoder.
For memristor-based delay element (MemDE), we applied a memristor between two
inverters to vary the path resistance, which determines the RC delay. This allows power
saving due to the low number of switching components and the absence of external delay
storage. We also investigate a solution for avoiding the unintended tuning (UT) and a
timing model to estimate the proper pulse width for memristance tuning. The simulation
results based on UMC 180nm technology and VTEAM model show the MemDE can
provide the delay between 0.55ns and 1.44ns which is compatible to the 4-bit multiplexerbased
delay element (MuxDE) in the same technology while consuming thirteen times
less power. The key contribution within (i) is the development of low-power MemDE to
mitigate the timing mismatch caused by PVT variations.
To estimate the temperature effect on memristance, we develop an empirical temperature
model which fits both titanium dioxide and silver chalcogenide memristors. The
temperature experiments are conducted using the latter device, and the results confirm
the validity of the proposed model with the accuracy R-squared >88%. The memristance
decoder is designed to deliver two key advantages. Firstly, the temperature model is
integrated into the VTEAM model to enable the temperature compensation. Secondly, it
supports resolution scalability to match the energy budget. The simulation results of the
2-bit decoder based on UMC 65nm technology show the energy can be varied between
49fJ and 98fJ. This is the second major contribution to address the challenge (ii).
This thesis gives future research directions into an in-depth study of the memristive
electronics as a variation-robust energy-efficient design paradigm and its impact on
developing future IoT applications.sponsored by the Royal Thai Governmen
Controller with Vehicular Communication Design for Vehicular Platoon System
Get PDFPhD ThesisTracked Electric Vehicles (TEV) which is a new mass-transport system. It aims to provide
a safe, efficient and coordinated traffic system. In TEV, the inter-vehicular distance is
reduced to only a quarter of the regular car length and where drive at 200km/h enabling
mass transport at uniform speed. Under this requirement, the design of the controller is
particularly important. This thesis first developed an innovative approach using adaptive
Proportion, integral and derivation (PID) controller using fuzzy logic theory to keep variable
time-gap between dynamic cars for platooning system with communication delay. The
simulation results presented show a significant improvement in keeping time-gap variable
between the cars enabling a safe and efficient flow of the platooning system. Secondly,
this thesis investigates the use of Slide Mode Control (SMC) for TEV. It studies different
V2V communication topology structures using graph theory and proposes a novel SMC
design with and without global dynamic information. The Lyapunov candidate function was
chosen to study the impact which forms an integral part for current and future research. The
simulation results show that this novel SMC has a tolerance ability for communication delay.
In order to present the real time TEV platoon system, a similar PI controller has been utilized
in a novel automated vehicle, based on Raspberry Pi, multi-sensors and the designed Remote
Control (RC) car. Thirdly, in order to obtain precise positioning information for vehicles in
platoon system, this thesis describes Inertial Measurement Unit (IMU)/Global Navigation
Satellite System (GNSS) data fusion to achieve a highly precise positioning solution. The
results show that the following vehicles can reach the same velocity and acceleration as the
leading vehicle in 5 seconds and the spacing error is less than 0.1m. The practical results are
in line with those from the simulated experiment
Thyroxine in Acute Myocardial Infarction (ThyrAMI)
Get PDFPh. D. ThesisImportance: Thyroid hormones play a key role in modulating myocardial contractility and
vascular function. Subclinical hypothyroidism is associated with worse cardiovascular
outcomes, in those without cardiovascular disease, and a poor prognosis in patients with acute
myocardial infarction.
Objective: To evaluate the effect of levothyroxine treatment on left ventricular function,
markers of vascular function and patient reported outcomes in patients with acute myocardial
infarction and subclinical hypothyroidism.
Hypotheses: Levothyroxine treatment will improve left ventricular function as a primary
outcome measure. Furthermore, levothyroxine treatment will decrease thrombus burden,
improve clot kinetics, platelet reactivity and endothelial function as well as patient reported
outcomes.
Design, Setting, and Participants: A double blind, randomized clinical trial conducted in six
hospitals in the United Kingdom. Patients with acute myocardial infarction including STsegment elevation and non-ST-segment elevation were recruited between February 2015 and
December 2016 with the last participant being followed up in December 2017.
Interventions: Levothyroxine treatment (n=46) commencing at 25 mcg titrated to aim for
serum thyrotropin levels between 0.4 and 2.5 mU/L or identical placebo (n=49), both provided
in capsule form, once daily for 52 weeks.
Main outcomes and measures: The primary outcome measure was left ventricular ejection
fraction at 52 weeks, assessed by magnetic resonance imaging, adjusted for age, sex, type of
acute myocardial infarction, affected coronary artery territory and baseline left ventricular
ejection fraction. Secondary outcomes were surrogate markers of vascular function and patient
reported outcome measures of health status, health-related quality of life, and depression.
ii
Results: Among the 95 participants randomized, the primary outcome measurements at 52
weeks were available in 85 (89.5%) patients. The mean left ventricular ejection fraction at
baseline and at 52 weeks was 51.3% and 53.8% in the levothyroxine group compared to 54.0%
and 56.1% in the placebo group; adjusted difference in groups (95% confidence interval) of
0.76% (-0.93% to 2.46%), p=0.37. Levothyroxine treatment did not significantly decrease
thrombus burden, improve clot kinetics, decrease platelet reactivity or improve endothelial
function. Furthermore, patient reported outcomes were not significantly different between both
groups at the study end. There were 15 (33.3%) and 18 (36.7%) cardiovascular adverse events
in the levothyroxine and placebo groups, respectively.
Conclusions and relevance: In this preliminary study involving patients with subclinical
hypothyroidism and acute myocardial infarction, treatment with low dose levothyroxine,
compared to placebo, did not significantly improve left ventricular ejection fraction, markers
of vascular function and patient reported outcomes after 52 weeks. These findings do not
support treatment of subclinical hypothyroidism in patients with acute myocardial infarction
How may we understand the experiences of school belonging amongst students with refugee backgrounds?
Get PDFD. App. Ed. Psy. Thesis.Sense of belonging has been highlighted as a key factor in supporting refugee children in the
post-migration phase. In the systematic literature review, I explored factors that contribute to
a sense of belonging among refugee students in schools. This qualitative review was
conducted using thematic synthesis. This process generated four main themes: meaningful
contribution, positive and consistent relationships, emotionally safe classroom and acquiring
new language as factors contributing to the sense of belonging of refugee students in schools.
The need for further research to explore the sense of school belonging of refugee students
within the UK is highlighted.
The bridging document explored aspects of the research, such as my rationale for
choosing the topic area. This section also provided a link between the systematic literature
review and the empirical study. In this, I discussed my philosophical stance, methodological
decisions and ethical considerations.
The aim of the empirical research project was to explore the experience of school
belonging amongst secondary school refugee students in the Northeast of England (NE). This
study draws upon the Bio-Psycho-Socio-Ecological Model (BPSEM) of school belonging,
which understands the sense of belonging not as an individual attribute but as a result of
complex interacting factors. Due to the focus on subjective experiences, Interpretative
Phenomenological Analysis was utilised. Seven refugee students were interviewed using a
semi-structured interview about their experience of school belonging in the NE via the Zoom
video-conferencing platform. The questions were underpinned by the theoretical
understanding of school belonging from literature and four main themes were developed from
the data: agency, participation, safety, and separation. The themes were discussed in terms of
barriers and supporting factors to participants’ school belonging in the NE. Also, findings
were considered in light of relevant literature and the BPSEM. Both draw attention to the
need to consider this issue within school systems and inform how Educational Psychologists
might work within school systems to enable factors that support the school belonging of
refugee students
Developing tools to investigate initiating events of mitochondrial translation
Get PDFPhD ThesisMitochondria are the predominant source of adenosine triphosphate (ATP) in nucleated human
cells. ATP is required as cellular energy source and mitochondria synthesise ATP by coupling
the oxidative phosphorylation (OXPHOS) system. Mitochondria contain their own circular
DNA (mtDNA) which encodes 11 messenger RNA (mt-mRNA), 2 ribosomal RNA (mtrRNA), and 22 tRNA (mt-tRNA) molecules which are all utilized for the synthesis of 13
proteins, all key components of the multi-subunit OXPHOS complexes, by the mitochondrial
ribosome (mitoribosome). Much of the life cycle of mt-RNA and the process of translation is
still unclear, in particular a full understanding of mt-mRNA stability, delivery, and loading
onto the mt-SSU (or mitoribosomes) is lacking. The aim of this research was to investigate
these processes using super resolution imaging of mt-rRNA and proximity-dependent
proteomic analysis.
I have visualised mt-rRNA molecules beyond the diffraction limit by the development and
application of RNA Fluorescent In Situ Hybridisation (FISH) compatible with STimulated
Emission Depletion (STED) microscopy. This technique was used to validate the loss of the
16S mt-rRNA upon induction of the mitochondrially-targeted VapC20 endonuclease and has
contributed to a model wherein the formation of the monosome is an important factor in mtmRNA transcript stability.
To further understand the process of mt-mRNA loading onto the mitoribosome, I employed
proximity-dependent biotin identification (BioID) to uncover proteins which may be enriched
at the mitoribosome mt-mRNA entry site. Multiple mitoribosomal proteins were fused to the
BioID moiety, expressed in human cells, and screened for their ability to assemble into the
mitoribosome. Mass spectrometry was used to characterise the proximal interaction network
of MRPS39 and MRPS27 which uncovered the heterodimeric proteins PHB and PHB2. These
proteins were then investigated to further understand their roles in mitochondrial translation.
This thesis presents a thorough investigation into mt-RNA and mitochondrial translation and
provides tools and techniques that complement the current literature
Missed Opportunities: How the Taiping Rebellion and American Civil War Changed American Attitudes Towards the Chinese Empire and China, 1850-1865
Get PDFPh. D. Thesis.This thesis is entitled Missed Opportunities: How the Taiping Rebellion and American Civil
War Changed American Attitudes Towards the Chinese Empire and China, 1850-1865. It
explores how American ideas about the rebellion in China drew on the disparate American
understandings of citizenship, religion, revolution, violence, trade and war. By using an
entangled history methodology, this thesis demonstrates how communication between the
American community in Shanghai and the United States itself shaped the ways both
Americans in China and Americans at home understood events in China. The multitudes of
information which crossed the Pacific both ways meant Americans did not understand the
Taiping Rebellion in isolation, but with reference to the world around them and especially
the secession crisis and Civil War in the United States. This dissertation argues that, despite
a host of different ideas and stances on the whether the Taiping rebels might be beneficial
for both China and those Americans seeking to make money or spread the word of God in
the early 1850s, Americans of all political, religious and sectional backgrounds had come to
a broad consensus that the Taiping did not represent opportunity for the United States by
1865. This is because of a hardening in attitudes towards revolution and violence, as well as
a growing belief that the rebellion in China was standing in the way of American merchants
making money in China. Finally, we can learn from examining this subject that the Taiping
Rebellion was such actually something that Americans could rally around at a time of
disunity, and furthermore, explain that despite the instability within the United States,
Americans of all backgrounds looked to China as a land of opportunity and perhaps even
imperial ambition.Arts and
Humanities Research Counc
Modelling energy efficiency and performance trade-offs
Get PDFPhD ThesisPower and energy consumption in data centres is a huge concern for data centre
providers. As a result, this work considers the modelling and analysis of policy and
scheduling schemes using Markovian processing algebra known as PEPA. The first
emphasis was on modelling an energy policy in PEPA that dynamically controls the
powering servers ON or OFF. The focus is to identify and reflect the trade-off between
saving energy (by powering down servers) and performance cost. While powering down
servers saves energy, it could increase the performance cost. The research analyses the
effect of the policy on energy consumption and performance cost, with different combinations of dynamic and static servers used in the policy against different scenarios,
including changes in job arrival rate, job arrival duration and the time needed by
servers to be powered On and start process jobs. The result gave interesting outcomes
because every scenario is unique, and therefore, no server combinations were found to
give low energy and high performance in all situations.
The second focus was to consider the impact of scheduler’s choice on performance
and energy under unknown service demands. Three algorithms were looked at: task
assignment based on guessing size (TAGS), the shortest queue strategy and random
allocation. These policies were modelled using PEPA to derive numerical solutions in
a two servers system. The performance was analysed considering throughput, average
response time and servers’ utilisation. At the same time, the energy consumption
was in terms of total energy consumption and energy consumption per job. The
intention was to analyse the performance and energy consumption in a homogeneous
and heterogeneous environment, and the environment was assumed to be homogeneous
in the beginning. However, the service distribution was considered either a negative
exponential (hence relatively low variance) or a two-phase hyper-exponential (relatively
high variance) in each policy. In all cases, the arrival process has been assumed to
be a Poisson stream, and the maximum queue lengths are finite (maximum size is 10
jobs). The performance results showed that TAGS performs worse under exponential
- vii -
distribution and the best under two-phase hyper-exponential. TAGS produce higher
throughput and lower job loss when service demand has an H2 distribution. Our
results show that servers running under TAGS consume more energy than other policies
regarding total energy consumption and energy per job under exponential distribution.
In contrast, TAGS consumes less energy per job than the random allocation when the
arrival rate is high, and the job size is variable (two-phase hyper-exponential).
In a heterogeneous environment and based on our results on the homogeneous environment, the performance metrics and energy consumption was analysed only under twophase hyper-exponential. TAGS works well in all server configurations and achieves
greater throughput than the shortest queue or weighted random, even when the second
server’s speed was reduced by 40% of the first server’s in TAGS. TAGS outperforms
both the shortest queue and weighted random, whether their second server is faster or
slower than the TAGS second server. The system’s heterogeneity did not significantly
improve or decrease TAGS throughput results. Whether the second server is faster or
slower, even when the arrival rate is less than 75% of the system capacity, it approximately showed no effect. On the other hand, heterogeneity of the system has a notable
effect on the throughput of the shortest queue and weighted random. The decrease or
increase in throughput follows the trend of the second server performance capability.
In terms of total energy consumption, for all scheduling schemes, when the second
server is slower than the first server, the energy consumption is the highest among all
scenarios for each arrival rate. TAGS was the worst and consumed higher energy than
both the shortest queue strategy and weighted random allocation. However, in terms
of energy per job, when servers are identical, or server2 is faster, it was observed that
the shortest queue is the optimal strategy as long as the incoming jobs rate does not
exceed 70% of the system capacity ( arrival rate <15). Furthermore, the TAGS was
the best strategy when the incoming task rate exceeds 70% of the system capacity. So,
as more jobs are produced, the energy per job decreases eventually. Choosing the energy policy or scheduling algorithm will impact energy consumption and performance
either negatively or positively
The impact of corporate governance on major shareholdings : the case of Saudi Arabia
Get PDFPhD ThesisThe aim of this thesis is to examine whether the Corporate Governance (CG) structure in
potential investee companies in Saudi Arabia has an impact on major shareholders choices of
shares. Scholars argue that good CG practices provide investors with more confidence to invest
their wealth in capital markets especially in developing countries (McKinsey, 2000). Saudi
Arabia embraces unique cultural, economic, social, religious settings and is characterised with
a prevalent presence of major shareholders in the capital market that is accompanied by
allegedly weak legal settings, which was observed after the infamous collapse of the Saudi
capital market in February 2006 (Ramady, 2010; Al-Nodel and Hussainey, 2010; Al-Matari,
Al-Swidi and Fadzil, 2012).
In order to investigate the impact of corporate governance on major shareholdings in the Saudi
capital market, a full review of the CG evolution in Saudi Arabia is presented and two sets of
questions are identified to achieve the objectives of this thesis. To address the research
questions, this thesis employs triangulation (i.e., mixed methods, quantitative and qualitative)
and embraces agency theory as main theoretical framework. The quantitative assessment is
performed using a panel data analysis of 97 non-financial listed companies in the Saudi capital
market over the period from 2013 to 2017 (485 observations). The qualitative assessment is
performed by conducting semi-structured interviews with fifteen participants of different
categories of major shareholders within the Saudi capital market.
Overall, the regression analysis has shown that total major shareholdings have a significant
negative relationship with CG score. Some interviewees expressed similar views toward such
mechanisms as they are believed to be responsible for the limitation of their power over
investee firms. The results of regression analysis to each category of major shareholders have
revealed that the only categories that are significantly related to CG is wealthy families
(negative) and wealthy individuals (positive), which is also supported by the findings of the
qualitative assessment. The qualitative assessment of the rest of major shareholders categories
have provided mixed results concerning CG preferences. Few interviewees believe that some
parts of CG structure of investee firms play a role during the decision-making of their
investments. On the other hand, most interviewees have revealed that CG in general is not
taken into consideration when making investment decisions. This explains the insignificant
relationship between CG and most categories of major shareholders revealed by the regression
analysis.The government of Saudi Arabia and Imam
Abdulrahman Bin Faisal Universit
The Accuracy of Electron Density from Theory : Calculating Electric Field Gradients and X-ray Scattering for Molecules and Solutions
Get PDFPh. D. Thesis.Electron density is the principle determinant of the characteristic properties
of molecules, their structure and dynamics. For this reason it is vital
to ascertain accurate densities. One method of predicting electron densities
is density functional theory (DFT). It is derived from the Hohenburg-Kohn
theorem which states that an exact ground-state energy should yield an exact
electron density and vice versa. In reality the exact solution is not fully
known as exchange and correlation have to be estimated. Were it known,
accurate densities and energies could be calculated at a fraction of ab initio
computational cost. However, it is noted that functional methods have deviated
from the path to the exact functional due to energetic overfitting. This
study used the electric field gradient (EFG) as an electron-density probe to
facilitate comparison both to ab initio calculation (CCSD(T)) and microwave
spectroscopy for simple transition metal complexes and halogenated aromatic
compounds. EFGs improved with increased Hartree-Fock (HF) exchange
fraction encountered for higher rungs of Jacob’s Ladder due to selfinteraction
error (SIE) reduction. SIE cancellation was uneven between transition
metals, halogens and aromatic rings, causing functional-dependent
electronegativity. Electron density can also be inferred from X-ray scattering.
X-ray free-electron lasers (XFELs) are used to probe molecular structure
and dynamics on ultrafast time scales. Solutions contains additional
scattering signals other than the desired solute from the solvent and solutesolvent.
The solvent term can be extracted experimentally or via molecular
dynamics (MD) trajectories. Theory is also the only method of predicting the
solute-solvent term independently. The solvent force-field parameters can
be derived from experiment or theoretically from DFT calculation. The impact
of the chosen force field on the the predicted scattering profiles was
evaluated herein, Quantum Bespoke Kit (QUBE) and all-atom Optimised
Potentials for Liquid Simulations (OPLS-AA) force-fields were used to assess
theoretically- and experimentally-derived parameters respectively for
common solvents for the same test solute (I2). Force-field dependence is elucidated
for both terms due to differences in non-bonded parameters.There
also remains further investigation to better approximate experimental solvent
terms. Solute-solvent scattering occurs on comparable scales to the solute
scattering. XFELs have also been applied recently to improve understanding
metal-to-ligand charge transfer (MLCT) in transition metal complexes
and the influence of polar solvents in their structures. QUBE was
used to investigate the ground and excited states of [Cu(phen)2]+ and compared
to recent classical MD and quantum-mechanical/molecular mechanical
(QM/MM) simulations. It performed particularly well in regards to identifying
Cu-N bond asymmetry and solvent influence in the ligand-ligand
dihedral in the triplet state which were not identified in previous theoretical
investigation but in agreement with recent experimental understanding.
This improvement was attributed to its use of high-rung DFT in parameterisation
(wB97X-D). Overall this investigation evaluate thoroughly the current
state of theory in reproducing accurate electron densities, highlighting the
importance of reducing DFT SIE to improve density accuracy, which in turn
impacts force-field parameter quality, indicating that DFT improvement impacts
all branches of theoretical chemistry
Co-designing of an intervention to support health visitors’ implementation of practices recommended for prevention of excess weight gain in 0-2 year old children
Get PDFPh. D. Thesis.Background: Early rapid weight gain is a risk factor for later obesity. UK health visitors (HVs)
are well-positioned to address excessive weight-gain trends in early childhood. However,
HVs face unique barriers when caring for children under age two with excessive rates of
weight gain. Interventions that strengthen HVs’ role by addressing key barriers and
facilitators of implementation of recommended guidelines into routine practice are needed.
Aim: This research engaged with HVs to systematically design an intervention to support
their implementation of practice behaviours.
Methods: A mixed-methods evidence synthesis and series of interactive workshops with HVs
were conducted. HVs who are the recipients of the intervention provided their views of what
is important, relevant, and feasible in the local context. The findings of the workshops were
combined in an iterative process to inform the sequential steps of the Behaviour Change
Wheel framework and guide the process of designing the intervention.
Results: Theoretical analysis of the workshops revealed HVs’ capabilities, opportunities, and
motivations related to addressing early-childhood obesity prevention. Intervention
strategies deemed most likely to support implementation (enablement, education, training,
modelling, persuasion) were combined to design a face-to-face interactive training
intervention. Outcome measures to test feasibility, acceptability, and fidelity of delivery of
the proposed intervention were identified.
Discussion: An interactive training intervention has been designed, informed by behaviour
change theory, evidence, expert knowledge, and experiences of health visitors, in an area of
health promotion that is currently evolving. Future research should be directed to evaluate
the acceptability and feasibility of the intervention in a pilot trial. The use of a systematic
approach to the development process, identification of intervention contents and their
hypothesised mechanisms of action using standard terminology provides an opportunity for
this research to contribute to the body of literature on designing of implementation
interventions using a collaborative approach.Durham County Council, Newcastle
University, and Fuse, the Centre for Translational Research in Public Healt