441 research outputs found
An investigation of entorhinal spatial representations in self-localisation behaviours
Spatial-modulated cells of the medial entorhinal cortex (MEC) and neighbouring cortices are thought to provide the neural substrate for self-localisation behaviours. These cells include grid cells of the MEC which are thought to compute path integration operations to update self-location estimates. In order to read this grid code, downstream cells are thought to reconstruct a positional estimate as a simple rate-coded representation of space.
Here, I show the coding scheme of grid cell and putative readout cells recorded from mice performing a virtual reality (VR) linear location task which engaged mice in both beaconing and path integration behaviours. I found grid cells can encode two unique coding schemes on the linear track, namely a position code which reflects periodic grid fields anchored to salient features of the track and a distance code which reflects periodic grid fields without this anchoring. Grid cells were found to switch between these coding schemes within sessions. When grid cells were encoding position, mice performed better at trials that required path integration but not on trials that required beaconing. This result provides the first mechanistic evidence linking grid cell activity to path integration-dependent behaviour.
Putative readout cells were found in the form of ramp cells which fire proportionally as a function of location in defined regions of the linear track. This ramping activity was found to be primarily explained by track position rather than other kinematic variables like speed and acceleration. These representations were found to be maintained across both trial types and outcomes indicating they likely result from recall of the track structure.
Together, these results support the functional importance of grid and ramp cells for self-localisation behaviours. Future investigations will look into the coherence between these two neural populations, which may together form a complete neural system for coding and decoding self-location in the brain
Drones, Signals, and the Techno-Colonisation of Landscape
This research project is a cross-disciplinary, creative practice-led investigation that interrogates increasing military interest in the electromagnetic spectrum (EMS). The project’s central argument is that painted visualisations of normally invisible aspects of contemporary EMS-enabled warfare can reveal useful, novel, and speculative but informed perspectives that contribute to debates about war and technology. It pays particular attention to how visualising normally invisible signals reveals an insidious techno-colonisation of our extended environment from Earth to orbiting satellites
Security and Privacy for Modern Wireless Communication Systems
The aim of this reprint focuses on the latest protocol research, software/hardware development and implementation, and system architecture design in addressing emerging security and privacy issues for modern wireless communication networks. Relevant topics include, but are not limited to, the following: deep-learning-based security and privacy design; covert communications; information-theoretical foundations for advanced security and privacy techniques; lightweight cryptography for power constrained networks; physical layer key generation; prototypes and testbeds for security and privacy solutions; encryption and decryption algorithm for low-latency constrained networks; security protocols for modern wireless communication networks; network intrusion detection; physical layer design with security consideration; anonymity in data transmission; vulnerabilities in security and privacy in modern wireless communication networks; challenges of security and privacy in node–edge–cloud computation; security and privacy design for low-power wide-area IoT networks; security and privacy design for vehicle networks; security and privacy design for underwater communications networks
Metaverse. Old urban issues in new virtual cities
Recent years have seen the arise of some early attempts to build virtual cities,
utopias or affective dystopias in an embodied Internet, which in some respects appear to
be the ultimate expression of the neoliberal city paradigma (even if virtual). Although
there is an extensive disciplinary literature on the relationship between planning and
virtual or augmented reality linked mainly to the gaming industry, this often avoids design
and value issues. The observation of some of these early experiences - Decentraland,
Minecraft, Liberland Metaverse, to name a few - poses important questions and problems
that are gradually becoming inescapable for designers and urban planners, and allows
us to make some partial considerations on the risks and potentialities of these early virtual
cities
Synchronising Wisdom and Implementation: A Formal ODD Approach to Expressing Insights on Bullying
Paper IV and V is excluded from the dissertation until it is published.The Social Simulation methodology, a mix of traditionally unassociated fields, utilises computer models to describe, understand, predict, and reflect on social phenomena. The model creation process typically requires the integration of knowledge insights from academic and non-academic knowledge holders. To ensure model quality, different processes are established in an effort to verify the alignment of knowledge insights and their implementation in the simulation model by the modelling team. However, due to a lack of technical skills, knowledge holders, who may not fully understand the model code, often perform these verification checks indirectly, for example by evaluating conceptual model descriptions. Initially motivated to create quality models of social conflict, this dissertation approaches the model quality challenge with a Domain Specific Modelling (DSM) approach. The objective was to develop a DSM tool using the Design Methodology, supplemented by a case study to provide first-hand experience with the quality challenge. Based on our project requirements, we selected University bullying as the case study subject. The Design Methodology included the problem exploration, the identification of a DSM solution, the selection of a domain and programming language for the DSM tool, the agile development of the domain language aspects with test models, and a final evaluation using the case study model.acceptedVersio
Acoustic cavitation characterisation in viscous deep eutectic solvents for optimisation of sonoprocessing of technology critical materials
The UK alone produced a total of 1.6 Mt of electronic waste in 2019, containing approximately 380,000 kg of technology critical metals worth $148 M per annum. Within this, printed circuit boards (PCBs) are the largest source of metals from electronic waste, containing up to 30-40 wt.% of technology critical metals. Traditional recycling techniques lack selectivity and have significant environmental and health impact. Ionometallurgy is a promising new technique for recovering metals from electronic waste using deep eutectic solvents (DESs). These solvents offer distinct advantage over traditional techniques, including much lower temperature requirements, avoidance of toxic reagents and reduced water consumption. DESs are cheap, readily available and can be adapted for selectivity. Despite these advantages, DESs are limited by slow dissolution kinetics primarily due to slow mass transport associated with their high viscosities. Power ultrasonics presents a useful solution to these issues. Sonication in DES is hypothesised to increase mass transport, remove passivating surface layers and promote cavitation-mediated effects. However, study into the cavitation activity in solutions other than water are limited. For efficient processing, cavitation generated at the tip of a sonotrode as a function of input power is required.
This work is the first comprehensive investigation of cavitation in DESs, for process optimisation to enhance precious metal recycling. Detailed characterisation of the cavitation generated by two sonotrodes in a number of DESs of varying viscosity and water is performed. High-speed imaging (HSI) and acoustic detection from a novel in-house constructed cavitation detector, characterised and validated against a commercially available cavitation sensor (NPL CaviSensorTM), identifies potentially optimal sonication parameters in each liquid. Detailed characterisation of each DES combining synchronised acoustic detection and HSI reveals generation of specific cavitation dynamics and associated cavitation structure, often characterised by a densely packed bulbous cavitation cloud, generating multi-fronted shockwaves. The sonotrode is deployed in DES for the delamination of technology critical metals from waste PCBs. Sonication was observed to delaminate the metals from the PCB at a rate over thirty times faster than in silent conditions. Furthermore, an optimally identified lower power sonication was shown to delaminate a greater quantity of metals from the PCB compared to a higher power sonication, over the same duration. The sonotrode is also deployed to investigate delamination of alternative technology critical resources; lithium-ion batteries and photovoltaics, as well as for rate enhancement of electrodissolution of copper. Further collaborative studies investigate single-bubble dynamics for validation of modelling in the audible frequency range, with interesting potential applications.
The results of the studies in this thesis demonstrate the utility and validity of proper cavitation characterisation in solutions intended for sonoprocessing. This characterisation can be performed simply, using bespoke, cheap passive cavitation detectors to gather acoustic measurements at sufficiently fine incremental input powers. Identification of optimal powers of any ultrasonic system for maximum cavitation efficiency is of relevance to many potential processes. In particular, the need for green technologies for electronic waste recycling, could present an ideal problem that can be tackled by ultrasonically enhanced ionometallurgy
Business sustainability: understanding the influence of managers and stakeholders on adopting sustainability practices in Nigerian SMEs
A thesis submitted in partial fulfilment of the requirements of the University of Wolverhampton for the Degree of Doctor of Philosophy.The importance of small and medium enterprises (SMEs) in any economy must be balanced, yet hardly the sector attracts the needed attention for sustainability. This has led to unacceptable high mortality rates for the sector, especially in emerging contexts. Nevertheless, SMEs and sustainability agenda share significant melting pots of disrupting large-scale extreme poverty, among other benefits. Numerous literature supports this and acknowledges SMEs' potential for national employment, investment stimulation and gross domestic growth (GDP). This study aimed to unveil the impacts of managerial characteristics and stakeholders on Nigerian SME sustainability practices to understand SME business sustainability practices in developing countries. To fully investigate these impacts, three research questions enabled the navigation of this project. Firstly, to ascertain the current antecedents influencing SME sustainability practices. Secondly, we quizzed the relationship between the manager's characteristics and Nigerian SME sustainability practices. Furthermore, finally, we sort out how stakeholders influence SMEs' sustainability practices in Nigeria.
A qualitative research approach was adopted within an interpretivist philosophical paradigm to construct participants narrated perspectives of sustainability practices. Data were collected from twenty-two (22) Nigerian SME owners/managers and nine (9) stakeholders in semi-structured interviews, virtually. Participants' information was inductively condensed, analysed and thematically framed using the Upper Echelon and Stakeholder concepts. The findings were dimensionally extracted using Gioia's step/order analysis to develop a data structure for each research question.
The findings for the current antecedence include the political and governance dimension, the cultural and societal dimension, the economic dimension, and the business orientation dimension. In contrast, the findings for the relationship between managerial characteristics and sustainability practices include observable dimensions and cognitive values. The finding for stakeholder influence on sustainability practices includes the managerial alignment dimension and the dimension of stakeholders’ intervention. Asides from the contribution to knowledge, the result presented national, organisational and managerial practical implications. Diverse organisational and regulatory policy implications were also presented with future research directions
Understanding intestinal and pancreatic hormone secretion in health and type 2 diabetes: (pre-)clinical studies and technical innovations
The gastrointestinal (GI) tract and pancreatic islets are key components of the endocrine system, responsible for the release of an array of peptide hormones, which orchestrate metabolic homeostasis through regulation of energy intake, nutrient digestion, absorption and metabolism. Of numerous hormones released from the gut, the incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), govern the secretion of both insulin and glucagon from pancreatic islets. Together, these hormones play a critical role in maintaining glucose homeostasis. Disrupted secretion and/or action of the incretins and pancreatic hormones underpins the development of type 2 diabetes (T2D) - a global epidemic characterised by elevated blood glucose concentrations and associated with devastating micro- and macro-vascular complications. Accordingly, an improved understanding of the physiology and pathophysiology of GI and pancreatic hormones in health and T2D is of major relevance to the development of effective strategies to both prevent and better manage T2D. This thesis comprises a series of clinical and preclinical evaluations that provide novel insights into the determinants of GI and islet hormone secretion (Chapters 3-6). In addition, it details the cross-disciplinary collaborative development of two ‘organ-on-a-chip’ platforms for dissecting the secretory function of both intestinal tissues and pancreatic islets (Chapters 7-8). Chapter 1 provides an overview of the secretion and action of GI hormones arising from the complex interaction between luminal nutrients/bioactive compounds and the gut mucosa, and details conventional and innovative research tools/platforms that are indispensable for the investigation of GI hormone secretion. Chapter 2 summarises the molecular mechanisms underlying insulin secretion from pancreatic islets, with a focus on the role of Ca2+ signalling, and systematically reviews the development of diverse research platforms that are fundamental to progressing islet research. Given the substantial sex-related differences in glucose metabolism and risk of T2D, the study described in Chapter 3 explores the sex disparity in incretin hormone secretion, and compares the incretin and glycaemic responses to standardised intraduodenal glucose infusions within the physiological range of gastric emptying between healthy young men and women. While insulin resistance and consequently a relative deficiency in insulin secretion are recognised as key metabolic derangements in T2D, there is accumulating evidence indicating that excessive glucagon secretion also underpins the development of dysglycaemia during both the fasting and postprandial phases. In the liver, insulin and glucagon signalling pose counter-regulatory effects on hepatic glucose production. Alterations in hepatic function have the potential to disrupt hepatic insulin and glucagon signalling, leading to pathological changes in insulin and glucagon secretion. The study reported in Chapter 4 evaluates the relationships of blood glucose, plasma insulin, C-peptide and glucagon, both during fasting and after 75g oral glucose, with serum liver enzymes in healthy and T2D subjects, and in T2D subjects before and after a mixed meal. Given the major role of the rate of gastric emptying (GE) in determining nutrient digestion and absorption, GE may influence the glucagon and glycaemic responses in T2D. Therefore, Chapter 5 further examines the relationships of plasma glucagon and blood glucose with the rate of gastric emptying (GE) of a standardised mashed potato meal in individuals with well-controlled T2D. Strategies that are effective for modulating GI and pancreatic hormone secretion have the potential to improve glycaemic control in T2D. The recent recognition that the GI tract can detect a range of physiological and pharmacological bitter substances via a family of type 2 monomeric G-protein-coupled receptors, namely bitter taste receptors (BTRs), to release GI hormones has led to growing interest in the administration of bitter tastants to stimulate GI hormone secretion for the management of metabolic disorders, including T2D. However, the effects of bitter substances beyond the GI tract have received little attention. Chapter 6 reports the effect of a bitter substance, denatonium benzoate (DB), on insulin secretion in a series of in vitro and ex vivo experiments using a rodent pancreatic β-cell line, INS-1 832/13 cells, and isolated mouse pancreatic islets. In the latter, the effects of DB on the secretion of other islet hormones, including glucagon, GLP-1 and somatostatin, were also characterised. While the currently available cell/tissue models and in vivo tools have substantially advanced the knowledge on the physiology and pathophysiology of incretins and islet hormones, there is rising demand for sophisticated biomimetic platforms to address the increasingly complicated biological challenges and improve the translational success from benchtop to bedside. To this end, the development of a gut-on-a-chip (GOC) system is described in Chapter 7 which facilitates continuous monitoring of dynamic GLP-1 secretion from primary mouse intestinal tissue. Similarly, the development and customisation of a microfluidic sensing platform is described in Chapter 8, allowing quantification of the dynamic changes of Ca2+ and insulin concurrently, enabling investigation of the secretory function of isolated islets.Thesis (Ph.D.) -- University of Adelaide, Adelaide Medical School, 202
Rapid learning of predictive maps with STDP and theta phase precession
The predictive map hypothesis is a promising candidate principle for hippocampal function. A favoured formalisation of this hypothesis, called the successor representation, proposes that each place cell encodes the expected state occupancy of its target location in the near future. This predictive framework is supported by behavioural as well as electrophysiological evidence and has desirable consequences for both the generalisability and efficiency of reinforcement learning algorithms. However, it is unclear how the successor representation might be learnt in the brain. Error-driven temporal difference learning, commonly used to learn successor representations in artificial agents, is not known to be implemented in hippocampal networks. Instead, we demonstrate that spike-timing dependent plasticity (STDP), a form of Hebbian learning, acting on temporally compressed trajectories known as 'theta sweeps', is sufficient to rapidly learn a close approximation to the successor representation. The model is biologically plausible - it uses spiking neurons modulated by theta-band oscillations, diffuse and overlapping place cell-like state representations, and experimentally matched parameters. We show how this model maps onto known aspects of hippocampal circuitry and explains substantial variance in the temporal difference successor matrix, consequently giving rise to place cells that demonstrate experimentally observed successor representation-related phenomena including backwards expansion on a 1D track and elongation near walls in 2D. Finally, our model provides insight into the observed topographical ordering of place field sizes along the dorsal-ventral axis by showing this is necessary to prevent the detrimental mixing of larger place fields, which encode longer timescale successor representations, with more fine-grained predictions of spatial location
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