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The Estimation of Stratospheric Aerosol Optical Depth from Measurements of Stellar Extinction
Get PDFStratospheric aerosol optical depth (SAOD) data is obtained for the period 1955-present based on measurements of starlight intensity by ground-based astronomical equipment. These measurements of intensity at different stellar zenith angles allow for the calculation of optical depth, a quantity measuring how much light is extinguished by the atmosphere for a given time and location. This data presents an exciting opportunity to supplement measurements of SAOD in periods where satellite data is either sparse or non-existent. The use of astronomical observations to reconstruct SAOD was pioneered by Richard Stothers (Stothers, 2001), who published hemispheric annual means for SAOD using astronomy data from 1961-1979. This
reconstruction is still a component of SAOD reconstructions used in climate modeling today. This period, referred to here as the Stothers period, fills a gap between SAOD reconstructions using ice cores and satellite instruments (1979-present). Stothers claimed that the astronomy data is the most accurate source of SAOD information in this period. However, this claim has yet to be substantiated as no quantified values of uncertainty were presented and only minimal comparisons to other methods were made. Therefore, it is not currently clear how accurately the astronomy data represents the true SAOD in the Stothers period. To establish uncertainty in this period, a comprehensive literature search for was done for astronomical optical depth measurements in the modern period. Six observing sites with long term time series data in the modern period were chosen. These sites include Canary Islands, Flagstaff, Washington Camp, and San Pedro Martir in the Northern Hemisphere, as well as Cerro Tololo and La Silla Tololo in the Southern Hemisphere. The Stothers method was applied to measurements at these sites in addition to several other observing sites with shorter coverage to deduce SAOD from astronomical data in both the pre-satellite and modern periods. The GloSSAC stratospheric aerosol reconstruction, based primarily on satellite data is taken to be the true value of SAOD in the modern period and the error in the astronomy data is obtained by considering the standard deviation in difference between the measurements. Using this method, a value for the typical error of ±0.0176 with a mean percent difference of ∼13% was found for annual means of SAOD obtained from astronomical measurements in the Northern Hemisphere and ±0.0169 with a mean percent difference of ∼16% in the Southern Hemisphere, leading to a global average error of ±0.0173 with a mean percent difference of ∼14.5%. This error estimate can be used to impose constraints on values of SAOD obtained from astronomical data in the pre-satellite era and will inform more robust quantification of the effect of volcanic eruptions on 20th century global mean temperature variability
Infrared Spectroelectrochemical Studies of Redox-Active Self Assembled Monolayers: Structure and Kinetics
Get PDFLong-range bridge-mediated electron transfer proceeding through outer-sphere pathways attracts scientific interest beyond fundamental studies due to its relevance in technological systems like molecular electronics and biosensors. Deep knowledge of the structure and dynamics of these molecular interfaces and the kinetics of the electron transfer processes are critical to improving the performance of such technological systems. Interfacial charge transfer between the electrode and redox molecules can be manipulated as an outer sphere electron transfer process by employing organic molecules as bridging moieties between the electron donor and acceptor. Electrode surfaces can be made suitable for charge transfer studies via the self assembled monolayers (SAMs) of redox-substituted alkanethiols. Alternatively, redox species can be covalently tethered to the terminals of preformed monolayers of alkane chains. Electroactive surfaces prepared via both methodologies are explored for studying heterogeneous electron transfer (ET) processes using conventional electrochemical techniques such as cyclic voltammetry and chronocoulometry. Butler-Volmer (BV) formalism and Marcus-Hush-Chidsey (MHC) theory are some of the widely accepted models to predict the kinetic parameters of electron transfer processes. In-situ surface characterization techniques such as surface-enhanced infrared absorption spectroscopy (SEIRAS) offer the potential to provide deeper insights into molecular processes occurring in organized systems during electron transfer. Time-resolved SEIRAS technique is an advanced method capable of correlating structural changes in both the redox-active moiety and the scaffold supporting the redox centre preceding/during/following the electron transfer process. This thesis reports a combination of time-resolved SEIRAS with conventional electrochemistry techniques to study the electron transfer process across different electroactive layers. The time-resolved SEIRAS technique is applied here to follow the molecular restructuring of alkane-bridging moieties during the electron transfer process in ferrocene-SAM systems. The behaviour of surrounding SAM structures to the redox moieties during the electron transfer process is also explored using deuterated alkanethiols as diluents. An amide-coupling reaction is explored to link electroactive moieties to prefabricated alkanethiol SAM terminals. Studying the reaction mechanism of the amide-coupling process offers an opportunity to improve the reaction efficiency. Therefore, the
potential of electrochemical-SEIRAS has been leveraged to monitor the amide-coupling process on the monolayers under various reaction conditions. SEIRAS analysis identified that the reaction intermediates change
their rate of formation under the electrode potential control, which establishes proof for potential-dependent
reaction pathways for amide-coupling reactions. Another redox species studied in this body of research is 2,2,6,6- tetramethylpiperidine-1-oxyl (TEMPO ̇ ), a prominent organic free radical used as a catalyst in various industrial-scale processes. Electron transfer studies of TEMPO ̇ tethered to various lengths of alkanethiols
are reported in this thesis using conventional electrochemical techniques. Time-resolved SEIRAS studies of TEMPO ̇ -alkanethiol monolayers for structural and kinetic analysis are reported here for the first time. The SEIRAS analysis provides a molecular model showing the conformational change of TEMPO ̇ moieties along with structural reorientation of the alkane chain adlayers during the electron transfer process
Active Vibration Control of a Flexible Robotic Manipulator
No full textThe abstract of this item is unavailable due to an embargo
A Comparison of the Bidomain and EMI Models in Refractory Cardiac Tissue
Get PDFComputational cardiac modelling has made incredible strides over the past 40 years toward becoming an
integral component of healthcare. The majority of cardiac modelling is accomplished using the bidomain
or monodomain models, equations describing electrical conduction in cardiac tissue. These models use a
volume averaging approach in which the structure of individual cells is disregarded; instead, cells are treated
homogeneously as a continuum. Although this approach often provides an adequate view of cardiac activity
at the macro level, there are situations where this approximation is insufficient, such as when discontinuities
at the cellular level are implicated in a given disease or phenomenon. To address this, a more detailed tissue
model has recently been developed: the extracellular-membrane-intracellular (EMI) model. The EMI model
explicitly defines the extracellular, membrane, and intracellular compartments to form a highly detailed
model of cardiac tissue. However, this additional level of detail also poses a high computational cost.
This thesis investigates the trade-off that exists between the conventional bidomain model and the EMI
model. To do this, we carry out a comparison study. This constitutes the first EMI comparison study
that has been conducted outside of the research group that developed the model. Using both models, we
find the currents required to trigger consecutive action potentials at varying time intervals. We then use
these data points to construct refractory profiles for each model and compare these profiles against available
experimental data. Our findings demonstrate that within the framework of this study, the behaviour of the
EMI model is noticeably closer to experimental data than the behaviour of the bidomain model. These results
have implications on the way we approach tissue model selection in the future, as well as for our general
understanding of the refractory properties of cardiac tissue
Measuring and Characterizing (mis)compliance of the Android permission system
Get PDFWithin the Android mobile operating system, Android permissions act as a system of safeguards designed to restrict access to potentially sensitive data and privileged components. Multiple research studies indicate flaws and limitations of the Android permission system, prompting Google to implement a more regulated and fine-grained permission model. In spite of its newly-introduced complexity, misgranted permissions continue to present a significant risk to users.
We present research on theoretical and practical misuse of permissions using our methodology that leverages unified permissions and call mappings. To guide the automated evaluation of permission use and compliance in Android apps, we develop PChecker, a tool that reports permissions requested by and granted to Android devices.
We evaluate four versions of the Android Open Source Project code (major versions 10--13) and shed light on the prevalence of discrepancies between the official Android guidelines for permissions and their implementation in the Android platform source code. We use PChecker to analyze the permission use of 3,681 Android apps showing the common prevalence and occasional severity of non-compliance in real-world scenarios
Mayenite Composite Pellet Development and Applications for Chloride Removal for Saline Oilfield Groundwater
No full textThe abstract of this item is unavailable due to an embargo
Aptamer-Based Detection of Salivary Melatonin for Circadian Rhythm Sleep Disorders Monitoring
No full textThe abstract of this item is unavailable due to an embargo
Defining the LEGACY of the Maternal Vaginal Microbiome in Microbial Communities of the Infant Gut
Get PDFOver the past decade, small-scale studies have suggested that human colonisation by microbes begins in utero, as evidenced by detection of bacterial DNA in placental tissues and amniotic fluid. Others have suggested that caesarean section (CS) delivery causes dysbiosis in the infant gut microbiome directly due to a lack of exposure to maternal vaginal microbes and that this may be corrected by direct transfer of maternal vaginal microbes These controversial observations in the absence of robust supporting evidence highlight the need to study the acquisition and development of human microbiomes from birth.
In this thesis, I have studied the composition and development of the infant stool microbiome immediately following birth, up to three months of life, using a combination of culture-based and culture-independent methods, largely based on cpn60 amplicon sequencing. I demonstrated that the neonatal meconium microbiome is almost entirely comprised of exogenous contaminating DNA, arguing against an in utero colonisation hypothesis and highlighting the need for robust controls in all microbiome studies. I have also shown that the maternal vaginal microbiome composition at delivery does not affect the composition of the infant stool microbiome, and that the effect of birth mode on the latter is confounded by intrapartum antibiotic administration during delivery. Finally, I found that direct transmission of maternal vaginal microbes to the infant gut is generally limited, although still a possibility during vaginal delivery, and highlighted the likely role played by other maternal sources- such as breast milk and stool- in the development of the infant stool microbiome.
This work adds to the growing body of evidence showing that the gestational environment is largely sterile until birth and provides much-needed insight into one of the factors long speculated to impact the composition and maturation of the infant stool microbiome. That the maternal vaginal microbiome appears to have little impact on the latter suggests that attempts to correct birth mode-related dysbiosis using vaginal microbes are likely to be of limited efficacy and emphasises the need to focus on other, more influential factors
Amino acid functionalized nanodiamonds as nucleic acid delivery vectors: synthesis and optimization of histidine-modified nanodiamonds, biological interaction studies and utilization for nucleic acid therapeutics
Get PDFUtilization of siRNA as therapeutic agents requires sophisticated carriers capable of packing, protecting, transporting, and delivering them to the target cells in an intact form. Among many non-viral nucleic acid delivery vectors, nanodiamonds (NDs) have shown promise to serve this purpose.
Our group have covalently functionalized the surface of NDs with basic amino acids to impart a net positive charge facilitating complexation with negatively charged nucleic acids. The prototype lysine-NDs (K-NDs) exhibited excellent dispersion stability and cellular internalization of the siRNA, however, the transfection efficiency of K-NDs diamoplexes was sub-optimal due to endo-lysosomal entrapment in the cells. Therefore, current work focused on introducing histidine on the surface to modulate pH sensitivity of the NDs and facilitate endo-lysosomal escape of diamoplexes. Histidine was incorporated in the functionalization scheme in two configurations: (1) lysyl-histidine-NDs (HK-NDs) and (2) lysine/lysyl-histidine-NDs (H50K50-NDs) where histidine was attached to either 100% or 50% of the lysine residues on the surface. Upon encounter with the acidic medium of the endosomes, histidine undergoes protonation leading to a cascade of counter ion and water influx in the organelle, that leads to endosomal swelling and rupturing of the membrane, i.e., proton sponge effect. Timely release of diamoplexes from the endosomes prevents degradation of the siRNA and thus improves the overall transfection efficiency of the carrier.
Functionalization of NDs with lysine and lysyl-histidine amino acid conjugates was maintained with desired physicochemical properties i.e., particle size > K-NDs (~25%) > HK-NDs (~21%). All fNDs showed exit after 5 days, leaving less than 10% cells with diamonds. Unlike the K-NDs, histidine-modified fNDs showed successful endosomal escape process driven by histidine-mediated proton sponge effect. Finally, we established that fNDs are feasible as siRNA delivery vectors to target oncogenes overexpressed in hepatocellular carcinoma. Both HK-NDs and H50K50-NDs diamoplexes transfected the siRNA against anti-myeloid cell leukemia-1 (anti-MCL-1) i.e., the target oncogene overexpressed in hepatocellular carcinoma, exhibiting a decline in relative MCL-1 expression with respect to untreated cells by 45% and 61% respectively. H50K50-NDs performed ~ 1.3 times better than the gold standard Lipofectamine control. Furthermore, downregulation of MCL-1 oncogene increased the sensitivity of the cells by 1.8 times towards an apoptosis inducing drug melphalan. Overall, my work demonstrated that histidine-mediated pH modulation renders high efficiency to diamoplexes
A Step Toward Improving Healthcare Information Integration & Decision Support: Ontology, Sustainability and Resilience
Get PDFThe healthcare industry is a complex system with numerous stakeholders, including patients, providers, insurers, and government agencies. To improve healthcare quality and population well-being, there is a growing need to leverage data and IT (Information Technology) to support better decision-making. Healthcare information systems (HIS) are developed to store, process, and disseminate healthcare data. One of the main challenges with HIS is effectively managing the large amounts of data to support decision-making. This requires integrating data from disparate sources, such as electronic health records, clinical trials, and research databases. Ontology is one approach to address this challenge. However, understanding ontology in the healthcare domain is complex and difficult. Another challenge is to use HIS on scheduling and resource allocation in a sustainable and resilient way that meets multiple conflicting objectives. This is especially important in times of crisis when demand for resources may be high, and supply may be limited.
This research thesis aims to explore ontology theory and develop a methodology for constructing HIS that can effectively support better decision-making in terms of scheduling and resource allocation while considering system resiliency and social sustainability. The objectives of the thesis are: (1) studying the theory of ontology in healthcare data and developing a deep model for constructing HIS; (2) advancing our understanding of healthcare system resiliency and social sustainability; (3) developing a methodology for scheduling with multi-objectives; and (4) developing a methodology for resource allocation with multi-objectives.
The following conclusions can be drawn from the research results: (1) A data model for rich semantics and easy data integration can be created with a clearer definition of the scope and applicability of ontology; (2) A healthcare system's resilience and sustainability can be significantly increased by the suggested design principles; (3) Through careful consideration of both efficiency and patients' experiences and a novel optimization algorithm, a scheduling problem can be made more patient-accessible; (4) A systematic approach to evaluating efficiency, sustainability, and resilience enables the simultaneous optimization of all three criteria at the system design stage, leading to more efficient distributions of resources and locations for healthcare facilities.
The contributions of the thesis can be summarized as follows. Scientifically, this thesis work has expanded our knowledge of ontology and data modelling, as well as our comprehension of the healthcare system's resilience and sustainability. Technologically or methodologically, the work has advanced the state of knowledge for system modelling and decision-making. Overall, this thesis examines the characteristics of healthcare systems from a system viewpoint. Three ideas in this thesis—the ontology-based data modelling approach, multi-objective optimization models, and the algorithms for solving the models—can be adapted and used to affect different aspects of disparate systems