Dissertations / Theses on the topic 'Ecological Applications not elsewhere classified'

This thesis studies areas of image compression and relevant image processmg techniques with the application to Non-destructive Testing (NDT) images of aircraft components. The research project includes investigation of current data compression techniques and design of efficient compression methods for NDT images. Literature review was done initially to investigate the fundamental principles of data compression and existing methods of lossless and lossy image compression techniques. Such investigation provides not only the theoretical background, but also the comparative benchmarks for the research project. Chapter 2 provides general knowledge of image compression. The basic predictive coding strategy is introduced at the beginning of chapter 3. Fundamental theories of the Integer Wavelet Transform (IWT) can be found in chapter 4. The research projects proposed mainly three innovative methods for lossless compression of NDT images. Namely, the region-based method that employs region­oriented adaptation; the texture-based method that employs a mixed model for the prediction of image regions with strong texture patterns; and a hybrid method that utilizes advantages from both predictive coding and IWT coding. The main philosophy of lossless image compression is to de-correlate the original image data as much as possible by mapping from spatial domain to spatial domain in the predictive coding strategy or from spatial domain to transform domain in the IWT coding strategy. The proposed region-based method aims to achieve the best mapping by adapting the de-correlation to the statistical properties of decomposed regions using the component's CAD model. With the aid of component CAD models to divide the NDT images of aircraft components into different regions based on the material structures, the design of the predictors and the choice of the IWT are optimised according to the specific image features contained in each region having the same material structure. The texture-based method achieves the best de-correlation by using a mixed data model in the region possessing strong texture patterns. A hybrid scheme for lossless compression of the NDT images of aircraft components is presented. The method combines the predictive coding and the IWT. After region-based predictive coding, the IWT is applied to the error images produced for each decomposed region to achieve further image de-correlation by preserving the information contained in the error images with fewer transform coefficients. The main advantages of using the IWT are its multi-resolution nature and lossless property with integer grey level values in images mapped to integer wavelet coefficients. The proposed methods are shown to offer a significantly higher compression ratio than other compression methods. The high compression efficiency is seen to be achieved by not only a combination of the predictive coding and the IWT, but also optimisation in the design of the predictor and the choice of the transform according to the specific image features contained in each region having similar material structures.

This thesis described the research carried out on the development of a novel hardwired tactile sensing system tailored for the application of a next generation of surgical robotic and clinical devices, namely a steerable endoscope with tactile feedback, and a surface plate for patient posture and balance. Two case studies are examined. The first is a one-dimensional sensor for the steerable endoscope retrieving shape and 'touch' information. The second is a two-dimensional surface which interprets the three-dimensional motion of a contacting moving load. This research can be used to retrieve information from a distributive tactile sensing surface of a different configuration, and can interpret dynamic and static disturbances. This novel approach to sensing has the potential to discriminate contact and palpation in minimal invasive surgery (MIS) tools, and posture and balance in patients. The hardwired technology uses an embedded system based on Field Programmable Gate Arrays (FPGA) as the platform to perform the sensory signal processing part in real time. High speed robust operation is an advantage from this system leading to versatile application involving dynamic real time interpretation as described in this research. In this research the sensory signal processing uses neural networks to derive information from input pattern from the contacting surface. Three neural network architectures namely single, multiple and cascaded were introduced in an attempt to find the optimum solution for discrimination of the contacting outputs. These architectures were modelled and implemented into the FPGA. With the recent introduction of modern digital design flows and synthesis tools that essentially take a high-level sensory processing behaviour specification for a design, fast prototyping of the neural network function can be achieved easily. This thesis outlines the challenge of the implementations and verifications of the performances.

This thesis describes the work carried out on the development of a novel digit actuator system with tactile perception feedback to a user and demonstrated as a master-slave system. For the tactile surface of the digit, contrasting sensor elements of resistive strain gauges and optical fibre Bragg grating sensors were evaluated. A distributive tactile sensing system consisting of optimised neural networking schemes was developed, resulting in taxonomy of artificial touch. The device is suitable for use in minimal invasive surgical (MIS) procedures as a steerable tip and a digit constructed wholly from polymers makes it suitable for use in Magnetic Resonance Imaging (MRI) environments enabling active monitoring of the patient during a procedure. To provide a realistic template of the work the research responded to the needs of two contrasting procedures: palpation of the prostate and endotracheal intubation in anaesthesia where the application of touch sense can significantly assist navigation. The performance of the approach was demonstrated with an experimental digit constructed for use in the laboratory in phantom trials. The phantom unit was developed to resemble facets of the clinical applications and digit system is able to evaluate reactive force distributions acting over the surface of the digit as well as different descriptions of contact and motion relative to the surface of the lumen. Completing control of the digit is via an instrumented glove, such that the digit actuates in sympathy with finger gesture and tactile information feedback is achieved by a combination of the tactile and visual means.

In the face of climate change, what can art do? The question is both practical and ethical: a question of art's efficacy, its ways of working, and its uses to audiences. These intertwined questions are articulated in writing and film-making, both of which draw on an empirical method, alongside research into ethics, ecology, film history, the politics of climate change, and critiques of capitalism. I seek to represent the consequences of climate change as they are experienced by the inhabitants of the north of Scotland and Arctic Russia. Through writing and film I document and interpret changing relationships with the sea and the land, thus bringing to light the interplay of climate change with history and memory, and with the social, economic, environmental and political forces that are shaping places and lives. One of the research methods of this PhD is a form of fieldwork, consisting of recorded interviews and informal encounters, filming and note taking, which form the source material for a multi-vocal approach to writing and filmmaking. The written thesis consists of narrations of journeys, both actual and theoretical. I tell stories of journeys to the White Sea in northeastern Russia, and to the north Highlands and islands of Scotland, where the political, economic and environmental upheavals are emblematic of a geopolitical shift north. I examine how ideas of North and of the sea, of nature and landscape, contained in films, oral histories, myths and writings, contribute to contemporary perceptions of place. These ideas are analyzed further through Alexander Dovzhenko’s film Aerograd, and Michael Powell’s The Edge of the World. I shot the two films, Call of North and From Time to Time at Sea, alongside supplementary film works, in Northern Russia and the far north of Scotland, in Caithness, Orkney and during a sailing expedition to the Northern Isles with Cape Farewell. Concomitantly with the first person written narrative, they investigate the camera as a participant-observer, and the implied presence of a future audience. The familiar trope of anthropology whereby the observer influences what is observed is explored here within the context of film. Both the written and film works document disappearance: of individuals and their memories, of species, of ecosystems, of ways of life, of imagined worlds, and of entire societies as well as the vertiginous fear of the future annihilation of human civilization. At the same time a plurality of perspectives and voices are combined to produce polyphonic compositions that resist being reduced to pessimism. The documentation of disappearance is examined and articulated as a distinct response to an ethical and ecological imperative. Meanwhile, the works propose to speak to a future audience –– to speak not to the world as it is but as it could become.

"The Port Curtis estuary is a heavy industrial centre and an international harbour. Sources of chemical stressors are many and multiple contaminants anre likely to be transported to the estuary by air and/or water. To assess whether contaminants are accumulating in the estuary and to identify those of potential concern in the Port Curtis estuary a screening level ecological risk assessment (SLERA) and a screening level human health risk assessment (HHRA) were performed." -- abstract.. The Port Curtis estuary is a heavy industrial centre and an international harbour. Sources of chemical stressors are many and multiple contaminants arelikely to be transported to the estuary by air and/or water. To assess whether contaminants are accumulating in the estuary and to identify those of potential concern in the Port Curtis estuary a screening level ecological risk assessment (SLERA) and a screening level human health risk assessment (HHRA) were performed. The basic risk assessment framework developed by the USEPA (1998) was applied in this study. Conceptual models were developed to assist with planning and design of the study. Assessment endpoints were chosen through consultations with experts and stakeholders. For the SLERA, the study area was divided into seven geographical zones. Existing water and sediment data were collated and data gaps identified. Additional data were gathered from two water and sediment surveys conducted by the CRC for Coastal Zone Estuary and Waterway Management. Al, As, Cd, Cu, Cr, Fe, Hg, Ni, Pb, Se, Zn, fluoride, cyanide, polycyclic aromatic hydrocarbons (PAHs) and tributyltin (TBT) were chemicals examined in the SLERA. Chemicals were measured in water and sediments, and in seagrass (Zostera capricorni), oysters (Saccostrea sp.), and mud whelks (Telescopium telescopium). For the HHRA, levels of Al, As, Cd, Cu, Cr, Fe, Hg, Ni, Pb, Se, and Zn were measured in fish and shellfish likely to be consumed by humans, namely, barramundi (Lates calcarifer), sea mullet (Mugil cephalus), mud crab (Scylla serrata) and banana prawns (Penaeus merguiensis) and TBT was measured in the edible flesh of mud crab. A compilation of all the data for the SLERA was assessed by comparing the observed water and sediment concentrations with water quality and sediment quality guidelines (ANZECC/ARMCANZ 2000) and comparing the observed contaminant concentrations in biota at study sites with benchmarks derived from concentrations in biota at control sites and the literature. It was found that concentrations of dissolved metals in waters of the Port Curtis estuary were low and below levels of regulatory concern. Concentrations of metals in sediments were also low, except for As, Cr and Ni. However, background concentrations of these metals were high. At some sites, As was higher than background levels, therefore As was included as a contaminant of potential ecological concern (COPEC). Tributyltin and naphthalene concentrations in water and/or sediments also exceeded guideline values and were identified as COPECs. Contaminants found to be enriched in biota in the estuary were Al, As, Cu, Cr, Fe, Hg, Ni, Se, Zn, and TBT. Possible adverse effects to the assessment endpoints from enrichment of metals in the Port Curtis estuary and from concentrations ofTBT and naphthalene in water/sediments were discussed. For the screening level HHRA, chronic daily intakes (CDIs) of contaminants by adults and children consuming seafood from this region were compared to threshold toxicity values set by regulatory agencies (ATSDR 2001). To account for additivity of other chemicals, a hazard quotient greater than 0.1 indicated contaminant of potential concern (COPC). It was found that Hg in barramundi from this region was a COPC. The inclusion of concentrations in biota was important in the SLERA of the Port Curtis estuary as several metals were accumulating to high concentrations in biota, but were not accumulating to high concentrations in water and sediments. The concentrations of metals in the dissolved form and/or in sediments were determined as being of low ecological risk. The ability of biota to integrate fluctuating concentrations of metals over time and to reflect exposure via dietary uptake meant the inclusion of concentrations in biota allowed a more thorough investigation of the exposure of biota to contaminants in the Port Curtis estuary.

Heat can be used as a reliable biomarker of cell metabolism. Assessing changes in metabolic activity is useful to study normal bioactivity or factors which may stimulate or inhibit cell proliferation. Methods which measure the heat of cell metabolism over time must be sensitive to the small changes. Thermoelectric sensors, which work by the Seebeck effect, are one method which has shown adequate sensitivity. This type of sensor directly converts heat energy into electrical energy without the use of a power source. Current research into sensors for cell metabolism may list lengthy, complex, and expensive procedures or include materials with rare or toxic elements. This work establishes a design approach of a silicon-based thermoelectric sensor for cell metabolism measurement which incorporates abundant and non-toxic materials and a simple procedure based on standard MEMS fabrication methods. The foundation for the sensor design is discussed. Fabrication was done using optical lithography, reactive ion etching, and electron beam evaporation which are standard and well known in industry. Sensor quality was characterized successfully based on the defined design parameters. Preliminary data has been recorded on the Coli cell metabolism. Finally, recommendations to improve heat insulation, include sensor calibration, and optimize manufacturing parameters are given for future work on this design to advance sensitivity and commercial potential.

Laser shock imprinting (LSI) is a novel fabrication technique capable of manufacturing various membrane materials. This top-down imprinting process can fabricate membranes in high precision, high throughput, and large scalability. It reveals a variety of applications ranging from electronics to photonics, which is beneficial from its reliable and precise modulation of micro/nanostructures.

In this thesis, we firstly proposed and developed a cost-effective LSI process to manufacture hierarchical micro/nanostructured power generators. By combining the conventional soft lithography technique, LSI is well compatible with it to fabricate metal membranes towards soft templates. It is a significant progress from the originally-developed silicon wafer template layout because it effectively reduces the process cost by replacing sophisticatedly developed silicon wafers with low-cost photocurable polymers. In addition, the use of polymer expands the boundary limit of geometrical complexity from simple patterns to hierarchical structures, as a result, we successfully conducted LSI technology to fabricate biomimic leaf structures into metallic membranes with the help of soft SU-8 templates. These fabricated metallic membraned are used as water-driven triboelectric nanogenerators. In addition to the introduction of polymer template, we further developed a successive laser shock imprinting (SLSI) process to fabricate hierarchical nanostructures in a higher resolution. Typically, grating templates are collected via recycling blank discs and used as soft templates. Then multiple times of LSI process are conducted to manufacture membranes into complex nanostructures. The use of blank disc further reduces cost and increase process resolution. The highlight of this part of work is to feature the introduction of metallic thin films on disc template, which plays a significant role during this high strain rate imprinting process. Then, the imprinting mechanism was investigated through the finite element method to validate the experimental findings. Lastly, this soft template LSI process was applied to fabricate low dimensional materials such as nanowires (1D) and nanomembranes (2D), potentially introducing homogeneous and inhomogeneous strain field. Kelvin probe force microscopy was used to directly probe strain-induced changes. This soft-template LSI process reveals a new route of precisely fabricating low dimensional membranes into nanoelectronics systems.

Innovation is promoted as a means to address global environmental challenges and achieve resilience in the UN Sustainable Development Goals. Innovation allows for adaptation and transformation in socio-ecological systems as part of the adaptive cycle. Within resilience literature, there are myriad definitions of innovation and disagreement about how to motivate diffusion of innovation, making implementation and the sustainability of innovations difficult. Specifically, matching the correct innovation to a given challenge and motivating the adoption of the innovation remains a roadblock to using innovation to address global environmental change. Here we show that there are explicit conflicts among definitions of innovation, and that innovation in the field does not align with some of these definitions. We found that the diverse definitions of innovation show a more complex view of innovation than normative treatment in policy suggests. We also found that several interacting motivations affect long-term participation in certain innovation activities. We discovered that binary views of innovation as either incremental or radical are generally supported in examples of innovation in the field, although some of the most successful examples of innovation better aligned with a continuum view of innovation associated with the adaptive cycle. Our results add to the warm-glow hypothesis that for altruistic tasks, the degree of participation motivated by a warm-glow feeling which can be enhanced by other motivations. Contrary to crowding out theory, our results suggest that monetary incentives result in higher adoption in Malawi where cost of contributing is high. The findings demonstrate the complexity of innovation, the misalignment between policy and practice, and ways in which adoption might be optimized. This research is a starting point to inform discussion about pragmatic innovation typologies. Such a typology could help operationalize the SDGs by framing the innovation dialogue between policy and practice.

Devices that can process more information in reduced dimensions are essential for an increasingly information- and efficiency-driven future. To this end, nanocomposites are promising due to their inherent multifunctional properties and special behavior at the nanoscale. Vertically aligned nanocomposites (VANs) are particularly interesting because of their ability to self-assemble into anisotropic nanostructures and high density of heterointerfaces – characteristics which introduce unique functionalities and offer exciting new avenues for device applications. However, a vast majority of VAN systems are currently fabricated on single-crystal oxide substrates, which may be cost-prohibitive at large scales and are generally incompatible with the prevalent device fabrication techniques. Thus, integration of VAN thin films on silicon becomes a critical step toward implementing VANs in a well-established semiconductor manufacturing industry.

In this dissertation, the viability of oxide-metal and nitride-metal VAN thin films integrated on silicon substrates has been demonstrated through a set of unique buffer layer designs. For the first three systems presented in this dissertation, namely, LaSrFeO₄-Fe, BaTiO₃-Au, and BaTiO₃-Fe, microstructural and physical property (i.e. electrical, magnetic, and optical) analyses confirm their successful epitaxial growth on silicon, with only minor differences compared to their counterparts grown on single-crystal oxide substrates. For the fourth system, a new and robust TiN-Fe VAN has been proposed and demonstrated. The new TiN-Fe VAN system on Si exhibits superior magnetic properties and unusual optical properties. With further growth optimization and/or patterning techniques, VAN thin film integration on silicon presents itself as a feasible and cost-effective approach to designing electronic, spintronic, photonic, and sensing devices.

Cameras are widely used as sensors for a variety of engineering applications. In a typical video-based application, spatial segmentation is a fundamental step which provides the spatial positions of different targets for further analysis. In this thesis, we focus on videos analytics applied to the agricultural industry and describe several video segmentation methods in the context of two practical projects: autonomous farming vehicles and analysis of dairy cow health. In the autonomous farming vehicle project, we propose three spatial segmentation methods based on traditional video features to isolate the regions of the video frame where critical information appears. Two applications that apply the segmentation method are presented: farming activity classification and header-height control for a combine harvester. In the project on cow health, we propose a cow structural model based on the keypoints of joints from a side-view cow video. A detection system is developed using deep learning techniques to automatically extract the structural model from the videos. Based on this model, we also present a preliminary application which estimates the cow’s weight based on video information.

Project models the reliability of an urban water distribution network.. Reliability is one of the fundamental considerations in the design of urban water distribution networks. The reliability of a network can be modelled by the probability of the connectedness of a stochastic graph. The enumeration of a set of cuts of the graph, and the calculation of the disjoint probability products of the cuts, are two fundamental steps in the network reliability assessment. An improved algorithm for the enumeration of all the minimal cutsets of a graph is presented. Based on this, a recursive algorithm for the enumeration of all Buzacott cuts (a particular set of ordered cuts) of a graph has been developed. The final algorithm presented in this thesis incorporates the enumeration of Buzacott cuts and the calculation of the disjoint probability products of the cuts to obtain the network reliability. As a result, it is tightly coupled, and very efficient. Experimental results show that this algorithm has a higher efficiency than other reported methods. The parallelism existing in the reliability assessment is investigated. The final algorithm has been implemented in a concurrent computer program. The effectiveness of parallel programming techniques in reducing the computing time required by the reliability assessment has also been discussed.

This dissertation is a summary of the graduate study in the past few years. In first part, we develop efficient spectral methods for the spectral fractional Laplacian equation and parabolic PDEs with spectral fractional Laplacian on rectangular domains. The key idea is to construct eigenfunctions of discrete Laplacian (also referred to Fourier-like basis) by using the Fourierization method. Under this basis, the nonlocal fractional Laplacian operator can be trivially evaluated, leading to very efficient algorithms for PDEs involving spectral fractional Laplacian. We provide a rigorous error analysis for the proposed methods, as well as ample numerical results to show their effectiveness.

In this dissertation, the synthesis of the triplet absorptive topology is presented in detail. The coupling matrix of this topology is derived. The synthesis theory extends to arbitrary phase of the transmission line used in the topology. A new FSL that yields the state-of-the-art performance is proposed. It employs the triplet absorptive filter topology, which enables absorptive response in a wider tuning range, to achieve high isolation (70 dB) everywhere in its octave tuning range. This was not possible with any existing FSLs. This triplet filter topology also gives bandstop-to-all-pass response, which enables controlled attenuation, or variable-attenuation control. The filter is implemented in high-Q evanescent-mode cavity technology, which yields low insertion loss in all-pass response. The proposed FSL is integrated with feedback control loops to enable in-field operations. For one step further, the FSL system is redesigned for optimization of robustness and reliability without compromising the state-of-the-art RF performance.

The current global sustainability crisis is a cultural crisis (Bokova, 2013; NASA, 2018). This crisis is due largely to the negative effects created by the amorphous nature of neoliberalism (Gittins, 2010; Latouche, 2010a; Washington, 2015). The 2030 Agenda for Sustainable Development (United Nations Development Programme (UNDP), 2011) outlined seventeen goals sought to rectify this crisis. The practical realisation of these goals has proven elusive to those seeking social change as they navigate negative human behaviours in local social contexts. This research explored adult bullying behaviours as one way to examine the clash between neoliberal and sustainable systems and the dysfunctionalities found in this social dynamic at a local community level. Cross-case study research methodology generated qualitative data from economically focussed developments in two communities in regional Australia. The presence in each case study of social interactions between individuals advocating for the perpetuation of neoliberalism and people seeking sustainability aims guided the selection of cases for this research. This first case context was a community (Arendelle community) living, and co-existing, near a non-towered aerodrome. Historically a holiday destination, the community had a range of socio-economic groups and encompassed a number of nature reserves. The case begins in 2006 with the introduction of a regional aviation company moving into the area for the purpose of implementing a portion of an international aviation contract. The second case (Gumnut Landcare) was a semi-rural community near forest and protected natural areas. Evident in the daily life of the community was a high level of understanding and implementation of sustainability practices including many forms of sustainable eco-centric lifestyle. The area also had a European dairy farming history. This case began in 2001 with the initial negotiations to purchase a parcel of land for a community site development and the desire for a special interest group to develop much of the land for an 18-hole golf course. The cross-case analysis allowed the examination of issues that represented not only the comparison of adult bullying by those advocating neoliberal aims in each case but current topical concerns relating the impacts on elements of sustainability domains and achieving sustainability aims. This methodology and associated methods were suitable for a critical social constructionist form of interpretivist research. The data collection instruments included in-depth interviews (seven in the first case and six in the second); continual personal communication with key individuals in each case (a long-term RA committee member in Arendelle case and long-term permanent employee of Gumnut Landcare); documentary analysis of public, organisational and historical records; and researcher observations. This research contributed to the extension of our understanding of cross-case study research through the discovery of interconnected units of analysis. This strengthened the value of case study methodology in social-ecological research. A key concept that emerged in this research but was absent in the literature on social change towards sustainability, was the need for an understanding of human behaviours considered detrimental to achieving sustainability aims, in particular, adult bullying, and the skills to alleviate those behaviours. The research extended, therefore, on the theoretical understanding of adult bullying in the social-ecological contexts of sustainability at a local community level. Firstly, it extended on the literature that examines bullying in corporate settings by constructing a normalised pattern of bullying behaviour for business development at the community level. Secondly, three categories of social connections between bystanders who utilised bullying behaviours to support individual neoliberalists emerged in each case—minions, mates and linchpins. A deeper understanding of the perpetuation of this social normalisation of bullying transpired through the surfacing of the linchpin as a new type of bystander pivotal in linking the bullying events in both cases and these cases to the broader neoliberal system. The research contributed to greater theoretical clarity around the barriers to implementation of social change towards sustainability at the local community level. It filled a gap in the literature by providing a critical understanding of human behaviours detrimental to change towards sustainability, such as adult bullying behaviours, and their use to implement neoliberal aims. This included a heightened understanding of how community residents in both cases failed to identify or acknowledge the behaviours they experienced as bullying. The community residents’ lack of understanding of how bullying was normalised in the local context meant it was difficult for them to respond in ways that supported sustainable alternatives. This conundrum was exacerbated with the identification that some community members also lacked awareness that many of their everyday actions supported sustainability. This research provided a framework for future research into the social-ecological context of adult bullying behaviours in local community settings, particularly as they are manifested in the behaviours of those implementing neoliberal aims. Future research needs to extend on two knowledge bases in local communities. The first is local community identification and responses to alleviating neoliberal bullying. The second is a greater ability to identify, understand and safeguard sustainable behaviours at the community level. One avenue of future research identified was the development of community sustainability frameworks (CSFs) that incorporate these knowledge bases. These CSFs would need to be developed to coincide with the increased recognition that social change towards sustainability requires a transdisciplinary and in some communities a supradisciplinary approach to policy, research, and practice at all social levels.

The miniaturization of a MOSFET is the constant driving force in semiconductor technology over the decades. This scaling enables the realization of the ever complex and functional integration on a single chip where over tens of billions of transistors densely packed. Silicon (Si) is always the golden performer until recent years when the shrinking of a transistor becomes more and more difficult, due to phenomena such as short channel effect and mobility degradation, which is a challenge especially for atomic level scaling. The dawning of low dimensional materials, such as graphene, transition metal dichalcogenides (TMDs), black phosphorus (BP), with their natural atomically thin two-dimension (2D) layered structure and other novel properties, might serve as an alternative solution for ultimate scaling. However, the understanding of the electronic transport in these Van der Waals materials is still lacking.

In this research, the exploration of this material was first initiated on the vertical heterojunctions where two materials’ interfaces meet. Many previous literatures claimed this hetero-interface creates a P/N junction that results in a diode-like rectification. Yet, by careful analysis and comparing with our “real” vertical structures where the lateral components were eliminated, it is proved this rectification is a direct result from the contact region. The Schottky barrier on the drain side together with the gate effect is the true culprit.

Realizing how the Schottky barrier could be dominating in these 2D FETs, the second study is the Schottky barrier effect on the contact resistances and furthermore the mobility of the device. Because of the existence of the Schottky barrier between the channel and contact, the contact resistance is not negligible, unlike the ohmic contact for conventional Si MOSFETs. By comparing the intrinsic and extrinsic mobilities of TMD materials, It is found that the contact resistance’s response to the back gate, namely, the rate of how it changes with the back gate has a huge factor in determining whether the extrinsic field-effect mobility underestimates or overestimates its intrinsic mobility. This opens a new insight on the understanding of the transport mechanism under contacts for different TMDs.

With the understanding of the Schottky barrier FETs, lastly, the flexibility of these 2D materials is utilized to create high performance three-dimensionally stacked multi-channel FETs, from the inspiration of the Si gate-all-around nanosheet structure. A first-ever 3D integrated high performance MoS₂ device with two channels on top of each other was designed and fabricated, where the current is doubled with an extra layer of channel. The potential of these novel material to be implemented on the future generations of high-performance devices is demonstrated, shedding light on the prospect for extending the Moore’s Law with proper assistance from new materials.

To sustain the upcoming paradigm shift in computations technology efficiently, innovative solutions at the lowest level of the computing hierarchy (the material and device level) are essential to delivering the required functionalities beyond what is available with current CMOS platforms. Motivated by this, in this dissertation, we explore ferroelectric-based devices for steep-slope logic and energy-efficient non-volatile-memory functionalities signifying the novel device attributes, possibilities for continual dimensional scaling with the much-needed enhancement in performance.

Among various ferroelectric (FE) materials, Zr doped HfO₂ (HZO) has gained immense research attention in recent times by virtue of CMOS process compatibility and a considerable amount of ferroelectricity at room temperature. In this work, we investigate the Zr concentration-dependent crystal phase transition of Hf_1-xZ_xO₂ (HZO) and the corresponding evolution of dielectric, ferroelectric, and anti-ferroelectric characteristics. Providing the microscopic insights of strain-induced crystal phase transformations, we propose a physics-based model that shows good agreement with experimental results for 10 nm Hf_1-xZ_xO₂. Further, in a heterogeneous system, ferroelectric materials can exhibit negative capacitance (NC) behavior. Such NC effects may lead to differential amplification in local potential and can provide an enhanced charge and capacitance response for the whole system compared to their constituents. Such intriguing implications of NC phenomena have prompted the design and exploration of many ferroelectric-based electronic devices to not only achieve an improved performance but potentially also overcome some fundamental limits of standard transistors. However, the microscopic physical origin as well as the true nature of the NC effect, and direct experimental evidence remain elusive and debatable. To that end, in this work, we systematically investigate the underlying physical mechanism of the NC effect in the ferroelectric material. Based upon the fundamental physics of ferroelectric material, we investigate different assumptions, conditions, and distinct features of the quasi-static NC effect in the single-domain and multi-domain scenarios. While the quasi-static and hysteresis-free NC effect was initially propounded in the context of a single-domain scenario, we highlight that the similar effects can be observed in multi-domain FEs with soft domain-wall (DW) displacement. Furthermore, to obtain the soft-DW, the gradient energy coefficient of the FE material is required to be higher as well as the ferroelectric thickness is required to be lower than some critical values. Otherwise, the DW becomes hard, and their displacement would lead to hysteretic NC effects. In addition to the quasi-static NC, we discuss different mechanisms that can lead to the transient NC effects. Furthermore, we provide guidelines for new experiments that can potentially provide new insights on unveiling the real origin of NC phenomena.

Utilizing such ferroelectric insulators at the gate stack of a transistor, ferroelectric-field-effect transistors (FeFETs) have been demonstrated to exhibit both non-volatile memory and steep-slope logic functionalities. To investigate such diverse attributes and to enable application drive optimization of FeFETs, we develop a phase-field simulation framework of FeFETs by self-consistently solving the time-dependent Ginzburg-Landau (TDGL) equation, Poisson’s equation, and non-equilibrium Green’s function (NEGF) based semiconductor charge-transport equation. Considering HZO as the FE layer, we first analyze the dependence of the multi-domain patterns on the HZO thickness (T_FE) and their critical role in dictating the steep-switching (both in the negative and positive capacitance regimes) and non-volatile characteristics of FeFETs. In particular, we analyze the T_FE-dependent formation of hard and soft domain-walls (DW). We show that, T_FE scaling first leads to an increase in the domain density in the hard DW-regime, followed by soft DW formation and finally polarization collapse. For hard-DWs, we describe the polarization switching mechanisms and how the domain density impacts key parameters such as coercive voltage, remanent polarization, effective permittivity and memory window. We also discuss the enhanced but positive permittivity effects in densely pattern multi-domain states in the absence of hard-DW displacement and its implication in non-hysteretic attributes of FeFETs. For soft-DWs, we present how DW-displacement can lead to effective negative capacitance in FeFETs, resulting in a steeper switching slope and superior scalability. In addition, we also develop a Preisach based circuit compatible model for FeFET (and antiferroelectric-FET) that captures the multi-domain polarization switching effects in the FE layer.

Unlike semiconductor insulators (e.g., HZO), there are ferroelectric materials that exhibit a considerably low bandgap (< 2eV) and hence, display semiconducting properties. In this regard, non-perovskite-based 2D ferroelectric -In₂Se₃ shows a bandgap of ~1.4eV and that suggests a combined ferroelectricity and semiconductivity in the same material system. As part of this work, we explore the modeling and operational principle of ferroelectric semiconductor metal junction (FeSMJ) based devices in the context of non-volatile memory (NVM) application. First, we analyze the semiconducting and ferroelectric properties of the α-In₂Se₃ van der Waals (vdW) stack via experimental characterization and first-principles simulations. Then, we develop a FeSMJ device simulation framework by self-consistently solving the Landau–Ginzburg–Devonshire equation, Poisson's equation, and charge-transport equations. Our simulation results show good agreement with the experimental characteristics of α-In₂Se₃-based FeSMJ suggesting that the FeS polarization-dependent modulation of Schottky barrier heights of FeSMJ plays a key role in providing the NVM functionality. Moreover, we show that the thickness scaling of FeS leads to a reduction in read/write voltage and an increase in distinguishability. Array-level analysis of FeSMJ NVM suggests a lower read-time and read-write energy with respect to the HfO₂-based ferroelectric insulator tunnel junction (FTJ) signifying its potential for energy-efficient and high-density NVM applications.

Feature extraction is the main driving force behind the advancement of the image processing techniques infields suchas image quality assessment, objectdetection, and object recognition. In this work, we perform a comprehensive and in-depth study on feature extraction for the following applications: image macro-uniformity assessment, 2.5D printing quality assessment, streak defect detection, and pedestrian detection. Firstly, a set of multi-scale wavelet-based features is proposed, and a quality predictor is trained to predict the perceived macro-uniformity. Secondly, the 2.5D printing quality is characterized by a set of merits that focus on the surface structure.Thirdly, a set of features is proposed to describe the streaks, based on which two detectors are developed: the first one uses Support Vector Machine (SVM) to train a binary classifier to detect the streak; the second one adopts Hidden Markov Model (HMM) to incorporates the row dependency information within a single streak. Finally, a novel set of pixel-difference features is proposed to develop a computationally efficient feature extraction method for pedestrian detection.

This thesis is a collection of the three projects I have worked on at Purdue. The first is a paper on thermoacoustic tomography involving circular integrating detectors that was published in Inverse Problems and Imaging. Results from this paper include demonstrating that the measurement operators involved are Fourier integral operators, as well as proving microlocal uniqueness in certain cases, and also stability. The second paper, submitted to the Journal of Inverse and Ill-Posed Problems, is much more of an application of sampling theory in to the specific case of thermoacoustic tomography. Results from this paper include demonstrating resolution limits imposed by sampling rates, and showing that aliasing artifacts appear in predictable locations in an image when the measurement operator is under sampled in either the time variable or space variables. We also show an application of a basic anti aliasing scheme based on averaging of data. The last project moves slightly away from microlocal analysis and considers the uniqueness in medical imaging of the restricted Radon transform in even dimensions. This is the classical interior problem, and we show a characterization of the range of the Radon transform, and from this are able to obtain a characterization of the kernel of the restricted Radon transform. We include figures throughout to illustrate results.

Hypersonic flight causes ultra-high surface temperatures which are most intense on sharp leading edges. One way of reducing the surface temperature is to apply a high emittance ceramic (HEC) on the leading edge, increasing the radiation component of heat transfer. An ideal HEC must have a high emittance, while also possessing a strong ablation resistance. From a scientific standpoint, it would be helpful if emittance could be tailored at different wavelengths. For example, materials with tailorable emittance could be used to improve the efficiency of engines, thermo-photo voltaic cells, and other applications. The approach used to create a ceramic with tailorable emittance was to use two different rare-earth elements, adding them to an ultra-high temperature ceramic (UHTC) in small quantities. The samarium element was added to increase the emittance of the UHTC over a large wavelength range (visible to near infrared wavelengths, consistent with the temperature range expected for hypersonic flight), and the erbium element was added to decrease the emittance at specific wavelength ranges. The goal of this study was to create an UHTC with tailorable emittance while maintaining the required ablation resistance. Therefore, ZBS billets with five different Sm to Er ratios and with a nominal total amount of 3 mol.% dopant incorporated were prepared by sintering in vacuum to 2000 °C. The ablation resistance was evaluated by using an oxyacetylene torch and observing at exposure times of 60 s and 300 s, whereas the emittance was evaluated at the Air Force Research Lab facilities via a laser heating testing. The results for the ablation testing showed that ZrB₂-SiC (ZBS) billets co-doped with Sm and Er formed a beneficial c₁-(Sm/Er)_0.2Zr_0.8O_1.9 oxide scale as the majority phase, which is more thermally stable than the m-ZrO₂ oxide scale typically formed in oxidized ZBS systems, resulting in a more adherent oxide scale to the unreacted material. The crystalline oxide scale and the amorphous phase were formed by a convection cell mechanism where the c₁-(Sm/Er)_0.2Zr_0.8O_1.9 crystalline islands precipitate, grow, and coalesce. Moreover, differences in surface temperatures between ZBS samples with different dopant ratios suggest differences in spectral absorptance/emittance between each of the five compositions evaluated. Despite that the emittance profiles with varying Sm:Er molar ratios were similar because m-ZrO₂ was formed as the major oxide phase, the emittance study showed that the erbium oxide influences the emittance profile, as can be noted by the maximum and minimum emittance peaks. Furthermore, results showed that the emittance varies as a function of dopant(s) molar ratios and temperature at shorter wavelength ranges. These changes in the emittance are caused by the different Sm and Er concentration on the surface. Future work should be focused on producing the beneficial c₁-(Sm/Er)_0.2Zr_0.9O_1.8 phase directly from the manufacturing process, and therefore, maximize the effect of varying the Sm:Er molar ratios to tailor the emittance. Nonetheless, this study represents the first generation and reported emittance data of UHTC doping ZBS systems with both Sm and Er elements.

Digital image processing techniques have many significant applications in industry. In this thesis, we focus on three problems in digital image processing. These three problems involve halftone images, information encoding and decoding, image alignment, and deep learning.

Specifically, the first problem is based on data-bearing halftone images, which are an aesthetically pleasing alternative to barcodes. We address the issues generated in the camera captured image alignment process. We perform some theoretical analysis and validate it by simulation. We also provide an optimal solution to the problem.

The second problem is about the alignment technique on a 3D surface. We develop a pipeline of surfaces coding to solve the alignment issues on 3D surfaces, which includes oblique surfaces and cylindrical surfaces.

The third problem is related to image retrieval. We propose a deep learning based solution to the fashion image retrieval task. Fashion image retrieval is significant to improve the customers’ experience in online shopping. A fast, accurate shopping item information retrieval system based on the customers’ uploaded image has been built by us. A novel solution is provided, and it achieves state-of-art accuracy in shopping items’ information retrieval.