4,075 research outputs found
On the path integration system of insects: there and back again
Navigation is an essential capability of animate organisms and robots. Among animate organisms of particular interest are insects because they are capable of a variety of navigation competencies solving challenging problems with limited resources, thereby providing inspiration for robot navigation.
Ants, bees and other insects are able to return to their nest using a navigation strategy known as path integration. During path integration, the animal maintains a running estimate of the distance and direction to its nest as it travels. This estimate, known as the `home vector', enables the animal to return to its nest.
Path integration was the technique used by sea navigators to cross the open seas in the past. To perform path integration, both sailors and insects need access to two pieces of information, their direction and their speed of motion over time. Neurons encoding the heading and speed have been found to converge on a highly conserved region of the insect brain, the central complex. It is, therefore, believed that the central complex is key to the computations pertaining to path integration.
However, several questions remain about the exact structure of the neuronal circuit that tracks the animal's heading, how it differs between insect species, and how the speed and direction are integrated into a home vector and maintained in memory. In this thesis, I have combined behavioural, anatomical, and physiological data with computational modelling and agent simulations to tackle these questions.
Analysis of the internal compass circuit of two insect species with highly divergent ecologies, the fruit fly Drosophila melanogaster and the desert locust Schistocerca gregaria, revealed that despite 400 million years of evolutionary divergence, both species share a fundamentally common internal compass circuit that keeps track of the animal's heading. However, subtle differences in the neuronal morphologies result in distinct circuit dynamics adapted to the ecology of each species, thereby providing insights into how neural circuits evolved to accommodate species-specific behaviours.
The fast-moving insects need to update their home vector memory continuously as they move, yet they can remember it for several hours. This conjunction of fast updating and long persistence of the home vector does not directly map to current short, mid, and long-term memory accounts. An extensive literature review revealed a lack of available memory models that could support the home vector memory requirements.
A comparison of existing behavioural data with the homing behaviour of simulated robot agents illustrated that the prevalent hypothesis, which posits that the neural substrate of the path integration memory is a bump attractor network, is contradicted by behavioural evidence.
An investigation of the type of memory utilised during path integration revealed that cold-induced anaesthesia disrupts the ability of ants to return to their nest, but it does not eliminate their ability to move in the correct homing direction. Using computational modelling and simulated agents, I argue that the best explanation for this phenomenon is not two separate memories differently affected by temperature but a shared memory that encodes both the direction and distance.
The results presented in this thesis shed some more light on the labyrinth that researchers of animal navigation have been exploring in their attempts to unravel a few more rounds of Ariadne's thread back to its origin. The findings provide valuable insights into the path integration system of insects and inspiration for future memory research, advancing path integration techniques in robotics, and developing novel neuromorphic solutions to computational problems
Canada\u27s Evergreen Playground: A History of Snow in Vancouver
The City of Vancouver is not as snowy as the rest of Canada; rain, not snow, is its defining weather feature. But snow is a common seasonal occurrence, having fallen there nearly every winter since the 1850s. This dissertation places snow at the centre of the City of Vancouverâs history. It demonstrates how cultural and natural factors influenced human experiences and relationships with snow on the coast between the 1850s and 2000s. Following Vancouverâs incorporation, commercial and civic boosters constructed â and settlers adopted â what I call an evergreen mentality. Snow was reconceptualized as a rare and infrequent phenomenon. The evergreen mentality was not completely false, but it was not entirely true, either. This mindset has framed human relationships with snow in Vancouver ever since. While this idea was consistent, how coastal residents experienced snow evolved in response to societal developments (such as the rise of the automobile and the adoption of new snow-clearing technologies) and regional climate change.
I show that the history of snow in Vancouver cannot be fully understood without incorporating the southern Coast Mountains. Snow was a connecting force between the coastal metropolis and mountainous hinterland. Settlers drew snowmelt to the urban environment for its energy potential and life-sustaining properties; snow drew settlers to the mountains for recreation and economic opportunities. Mountain snow became a valuable resource for coastal residents throughout the twentieth century. Human relationships with snow in the mountains were shaped, as they were in the city, by seasonal expectations, societal circumstances, and shifting climate conditions.
In charting a history of snow in Vancouver and the southern Coast Mountains, this dissertation clears a new path in Canadian environmental historiography by bringing snow to the historiographical forefront. It does so in an urban space not known for snow, broadening the existing geography of snow historiography. In uncovering snowâs impact on year-round activities, this work also expands the fieldâs temporal boundaries. Through this work, one sees how snow helped to make Canadaâs Evergreen Playground
Conditional Tabular Generative Adversarial Net for Enhancing Ensemble Classifiers in Sepsis Diagnosis
Antibiotic-resistant bacteria have proliferated at an alarming rate as a result of the extensive use of antibiotics and the paucity of new medication research. The possibility that an antibiotic-resistant bacterial infection would progress to sepsis is one of the major collateral problems affecting people with this condition. 31,000 lives were lost due to sepsis in England with costs about two billion pounds annually. This research aims to develop and evaluate several classification approaches to improve predicting sepsis and reduce the tendency of underdiagnosis in computer-aided predictive tools. This research employs medical data sets for patients diagnosed with sepsis, it analyses the efficacy of ensemble machine learning techniques compared to non ensemble machine learning techniques and the significance of data balancing and Conditional Tabular Generative Adversarial Nets for data augmentation in producing reliable diagnosis. The average F Score obtained by the non-ensemble models trained in this paper is 0.83 compared to the ensemble techniques average of 0.94. Nonensemble techniques, such as Decision Tree, achieved an F score of 0.90, an AUC of 0.90 and an accuracy of 90%. Histogram-based Gradient Boosting Classification Tree achieved an F score of 0.96, an AUC of 0.96 and an accuracy of 95%, surpassing the other models tested. Additionally, when compared to the current state of the art sepsis prediction models, the models developed in this study demonstrated higher average performance in all metrics, indicating reduced bias and improved robustness through data balancing and Conditional Tabular Generative Adversarial Nets for data augmentation. The study revealed that data balancing and augmentation on the ensemble machine learning algorithms boost the efficacy of clinical predictive models and can help clinics decide which data types are most important when examining patients and diagnosing sepsis early through intelligent human-machine interface
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Alternative Power: The Politics of Denmark\u27s Renewable Energy Transition
Global climate change is one of the defining political challenges and opportunities of the current era. Experts widely agree that technical means already exist for making the necessary transition from fossil fuels to renewable energy; the obstacles to doing so are primarily political. Careful observers also recognize that this period of transition creates an opening for political innovation and development. How can the political will be generated to take action to prevent climate catastrophe? And what will the process of transitioning mean for the political systems that have been built on cheap and abundant oil? Political scientists have largely ignored technological development as a lever for political development, or feared that technology could only be a force of domination. Yet renewable energy enthusiasts have often seen democratizing potential in these technologies. What can be accomplished politically by building a wind turbine? As countries like Denmark accumulate decades of experience with renewable energy, it is becoming possible to give such questions close empirical consideration. Denmark generates more of its electricity from renewable sources, and has been doing so longer, than any other industrialized nation, making it a uniquely valuable case for studying an advanced renewable energy transition in progress. This dissertation draws on novel qualitative and quantitative data to present the first comprehensive history of Denmarkâs energy transition from its roots in the 1970s until the present, aiming to explain how this tiny nation emerged as the worldâs leading wind power producer, and assess whether this process has yielded any democratic dividends. The multi-method analysis sheds new light on internal dynamics of Denmarkâs energy transition, and, more generally, on late-stage evolutionary processes in mature technological systems. Many studies have shown an interest in the Danish case, which is usually presented as a relatively unqualified success story, but few have provided the empirical resolution to identify these complicating factors. This dissertation employs an explanatory strategy adapted from the ecological sciences to construct a more holistic and integrative portrait, resulting in a more thorough and accurate account of how Denmark jumped out to such a significant lead in the energy transition, and why that momentum might be flagging today, with implications for other countries hoping to chart a path toward a sustainable future
Quantification of forest carbon flux and stock uncertainties under climate change and their use in regionally explicit decision making: Case study in Finland
Uncertainties are essential, yet often neglected, information for evaluating the reliability in forest carbon balance projections used in national and regional policy planning. We analysed uncertainties in the forest net biome exchange (NBE) and carbon stocks under multiple management and climate scenarios with a process-based ecosystem model. Sampled forest initial state values, model parameters, harvest levels and global climate models (GCMs) served as inputs in Monte Carlo simulations, which covered forests of the 18 regions of mainland Finland over the period 2015â2050. Under individual scenarios, the results revealed time- and region-dependent variability in the magnitude of uncertainty and mean values of the NBE projections. The main sources of uncertainty varied with time, by region and by the amount of harvested wood. Combinations of uncertainties in the representative concentration pathways scenarios, GCMs, forest initial values and model parameters were the main sources of uncertainty at the beginning, while the harvest scenarios dominated by the end of the simulation period, combined with GCMs and climate scenarios especially in the north. Our regionally explicit uncertainty analysis was found a useful approach to reveal the variability in the regional potentials to reach a policy related, future target level of NBE, which is important information when planning realistic and regionally fair national policy actions.
A Correction to this article was published on 12 September 2023
Investigating Middle Stone Age foraging behaviour in the Karoo, South Africa
The Middle Stone Age (MSA) in Africa ~500- 50 kyr is recognised as a key time-period associated with important developments in hominin evolution, including the appearance of earliest genetic markers for Homo sapiens. Despite advances, our knowledge of the behaviour of hominins during this period is limited, especially for the early MSA (EMSA) pre-160ka. This study presents new data on animal bones recovered at the Bundu Farm site, in the upper Karoo region of the Northern Cape, South Africa, dated to circa ~300ka and found in association with EMSA type lithic facies, burning and hearth-like features. Previous analysis of the Bundu fauna compared the site to a G/wi hunter-gatherer 'biltong' processing locale, implying primary access to animal carcasses and socially complex hunting behaviour, circa 400-300 ka. An interpretation at odds with other interpretations of the EMSA data that suggest limited hunting and social complexity, and which would therefore have significant implications for MSA archaeology. To test the biltong hypothesis my study presents new data on the fracture characteristics of non-fresh animal bone broken by hammerstone and new environmental data for the site from an analysis of ostrich eggshell isotopes. Experimental and environmental data are used to provide a new interpretation of the Bundu fauna and my conclusion is that the data while not supporting the biltong model, does indicate evidence of delayed communal food consumption, use of fire and the transformation of foodstuffs into meals presaging and echoing social and ecological adaptations seen in the later MSA and LSA. The data also highlights a greater role for carnivores in the accumulation of the faunal assemblage and expedient hominin foraging similar to the preceding ESA and brings attention to the ecological relationships between hominins and carnivores in a Pleistocene Karoo environment that was markedly different from that of today. The study therefore rejects the biltong hypothesis for Bundu Farm as both inconsistent with likely EMSA social structures and ecology and instead proposes the site as evidence for novel behaviour indicative of a transition from ESA to MSA lifeways. The Bundu Farm site reflecting a rare archaeological occurrence where the shift in the behavioural trajectory that led to our species is observed
âAn interval of comfortâ: postamputation pain & long-term consequences of amputation in British First World War veterans, 1914-1985
The First World War resulted in the largest amputee cohort in history, with 41,208 amputees in the UK alone; the majority injured as young men and surviving into the late 20th century. Recent studies have estimated that significant residual limb pain affects up to 85% of military amputees: applying this figure to the First World War amputee cohort raises the possibility that up to 35,000 British veterans may have experienced chronic postamputation pain. Despite this and the fact that 13% of injuries in this conflict resulted in amputation, there has been little research into the long-term impact on veteransâ health and quality of life.
Recently catalogued historical medical and pension files held at The National Archives offer the opportunity to follow up this type of injury in a large group of veterans for the first time. This thesis will use these files to document and explore long-term outcomes of amputation and chronic postamputation pain, developments made in the treatment of this condition, the impact of aging on amputee veterans and their likelihood of developing a concomitant condition from 1914 to 1985. It will examine these issues from three perspectives: that of the injured servicemen, the civil servants attempting to value and compensate those injuries, and from the cliniciansâ responsible for the veteransâ medical care and rehabilitation. This research has been based on a unique model of interdisciplinary collaboration, incorporating research methods from history and clinical medicine, and will present its findings from historical material with recommendations for current practice.
Given the similarities in injury patterns and prevalence of chronic residual limb, phantom and neuropathic pain between the First World War cohort and contemporary casualties, it is anticipated that the findings of the project will assist in the strategic assessment and planning for long-term pain conditions by medical staff and care providers for todayâs and future blast injury amputee cohorts.Open Acces
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