10,524 research outputs found

    Identification of Hindbrain Neural Substrates for Motor Initiation in the hatchling Xenopus laevis Tadpole

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    Animal survival profoundly depends on the ability to detect stimuli in the environment, process them and respond accordingly. In this respect, motor responses to a sensory stimulation evolved into a variety of coordinated movements, which involve the control of brain centres over spinal locomotor circuits. The hatchling Xenopus tadpole, even in its embryonic stage, is able to detect external sensory information and to swim away if the stimulus is considered noxious. To do so, the tadpole relies on well-known ascending sensory pathway, which carries the sensory information to the brain. When the stimulus is strong enough, descending interneurons are activated, leading to the excitation of spinal CPG neurons, which causes the undulatory movement of swimming. However, the activation of descending interneurons that marks the initiation of motor response appears after a long delay from the sensory stimulation. Furthermore, the long-latency response is variable in time, as observed in the slow-summating excitation measured in descending interneurons. These two features, i.e. long-latency and variability, cannot be explained by the firing time and pattern of the ascending sensory pathway of the Xenopus tadpole. Therefore, a novel neuronal population has been proposed to lie in the hindbrain of the tadpole, and being able to 'hold' the sensory information, thus accounting for the long and variable delay of swim initiation. In this work, the role of the hindbrain in the maintenance of the long and variable response to trunk skin stimulation is investigated in the Xenopustadpole at developmental stage 37/38. A multifaceted approach has been used to unravel the neuronal mechanisms underlying the delayed motor response, including behavioural experiments, electrophysiology analysis of fictive swimming, hindbrain extracellular recordings and imaging experiments. Two novel neuronal populations have been identified in the tadpole's hindbrain, which exhibit activation patterns compatible with the role of delaying the excitation of the spinal locomotor circuit. Future work on cellular properties and synaptic connections of these newly discovered populations might shed light on the mechanism of descending control active at embryonic stage. Identifying supraspinal neuronal populations in an embryonic organism could aid in understanding mechanisms of descending motor control in more complex vertebrates

    The influence of blockchains and internet of things on global value chain

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    Despite the increasing proliferation of deploying the Internet of Things (IoT) in global value chain (GVC), several challenges might lead to a lack of trust among value chain partners, e.g., technical challenges (i.e., confidentiality, authenticity, and privacy); and security challenges (i.e., counterfeiting, physical tempering, and data theft). In this study, we argue that Blockchain technology, when combined with the IoT ecosystem, will strengthen GVC and enhance value creation and capture among value chain partners. Thus, we examine the impact of Blockchain technology when combined with the IoT ecosystem and how it can be utilized to enhance value creation and capture among value chain partners. We collected data through an online survey, and 265 UK Agri-food retailers completed the survey. Our data were analyzed using structural equation modelling (SEM). Our finding reveals that Blockchain technology enhances GVC by improving IoT scalability, security, and traceability when combined with the IoT ecosystem. Which, in turn, strengthens GVC and creates more value for value chain partners – which serves as a competitive advantage. Finally, our research outlines the theoretical and practical contribution of combining Blockchain technology and the IoT ecosystem

    Adaptive task selection using threshold-based techniques in dynamic sensor networks

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    Sensor nodes, like many social insect species, exist in harsh environments in large groups, yet possess very limited amount of resources. Lasting for as long as possible, and fulfilling the network purposes are the ultimate goals of sensor networks. However, these goals are inherently contradictory. Nature can be a great source of inspiration for mankind to find methods to achieve both extended survival, and effective operation. This work aims at applying the threshold-based action selection mechanisms inspired from insect societies to perform action selection within sensor nodes. The effect of this micro-model on the macro-behaviour of the network is studied in terms of durability and task performance quality. Generally, this is an example of using bio-inspiration to achieve adaptivity in sensor networks

    3D printed Microneedles for Transdermal Drug Delivery

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    3D printing is a revolutionary manufacturing and prototyping technology that has altered the outlooks of numerous industrial and scientific fields since its introduction. Recently, it has attracted attention for its potential as a manufacturing tool for transdermal microneedles for drug delivery. In the present thesis, the 3D printability of solid and hollow microneedles via photopolymerisation-based 3D printing was investigated, aiming at establishing robust manufacturing strategies for reproducible, mechanically strong and versatile microneedles. The developed microneedles were employed as drug delivery systems for the treatment of diabetes via insulin administration. Solid microneedles featuring different geometries were designed and 3D printed. It was demonstrated that the printing and post-printing parameters affected the printed quality, a finding that was employed to optimise the manufacturing strategy. Microneedle geometry was also found to have an impact on the piercing and fracture behaviour; however all microneedle designs were found to be mechanically safe upon application. The solid microneedles were subsequently coated with insulin-polymer films, using a 2D inkjet printing technology. The coating process achieved spatial control of the drug deposition, with quantitative accuracy. The microneedle geometry was shown to influence the morphology of the coating film, an effect that was pronounced during in the in vitro delivery studies of insulin to porcine skin. Furthermore, hollow microneedles were designed and 3D printed, featuring different heights. Two photopolymerisation-based technologies were studied, and their performance was compared. The key influential parameters of the printing outcome and microneedle quality were identified to be the printing angle and the size of the microneedle opening. The hollow microneedles were found to be effective in piercing porcine skin without structural damaging. The hollow microneedles were incorporated into complex patches with internal microfluidic structures for the provision and distribution of drug-containing solutions. The developed complex hollow microneedle patches were coupled with a microelectromechanical system to create a novel platform device for controlled, personalised transdermal drug delivery. Advanced imaging techniques revealed that the device achieved distribution of the liquid within porcine skin tissue without the creation of depots that would delay absorption. The device was evaluated for its efficacy to transdermally deliver a model dye and insulin in vitro. In vivo trials were also conducted using diabetic rodents, with the device achieving faster onset of insulin action and sustained glycemic control, in comparison to subcutaneous injections. Overall, the findings of the present research are anticipated to elucidate key problematic areas associated with the application of 3D printing for microneedle manufacturing and propose feasible solutions. The outermost goal of this work is to contribute to the advancement of knowledge in the field of 3D printed transdermal drug delivery systems, in order to bring them one step closer to their adoption in the clinical setting

    Understanding and Engineering of Sub-gap States in Photodetection

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    Emerging applications for light sensing, including wearable electronics, internet of things and autonomous driving, are pushing conventional semiconductors technologies to their limits when it comes to ease of fabrication, power consumption and device design. Organic semiconductors are considered next-generation absorber materials for photodetection in the visible and near infrared part of the electromagnetic spectrum, which hold some promise of addressing the aforementioned problems of conventional materials. So far, only a handful of companies are putting organic semiconductors to the test for commercial photodetectors, however, research on organic photodetectors is thriving – in particular on photodetectors with a diode architecture called photodiodes. The goal is to make flexible, light-weight devices with improved performance metrics and high stability to realize viable alternatives to conventional photodiodes. The performance limits of organic photodiodes are often associated with the presence of electronic states with energies below the bandgap edge – the so-called sub-gap states. A powerful tool to study the properties of sub-gap states is to measure the external quantum efficiency (EQE), however, the subsequent analysis is complicated by the presence of static disorder and optical interference. In the first part of this work, it is shown how the true absorption coefficient can be extracted from a series of interference affected sub-gap EQE spectra of organic photodiodes with different thicknesses. In consequence, the effect of chemical structure modification on the absorption coefficient in the spectral range of charge transfer absorption is demonstrated. By adjusting the molecular energy levels through target chemical substitutions, a redshift and an increase of the oscillator strength are achieved. The increased spectral coverage in the near infrared is then exploited in micro-cavity photodiodes. The second part of this work deals with the sub-gap absorption coefficient of donor and acceptor materials and how it is affected by the molecular energy level offset. For materials with low energetic offset, it is shown that the sub-gap absorption coefficient follows the Urbach rule in the spectral range of excitonic absorption, dictating the broadening of the sub-gap absorption coefficient at energies right below the bandgap. Lastly, the origin of the high dark current in organic photodiodes is identified as non-radiative recombination via mid-gap trap states. An upper limit to the specific detectivity is calculated that is expected viable in organic photodiodes. The findings of this thesis contribute to the understanding of the sub-gap states by studying their absorption features and distinguishing them from the ubiquitous optical interference effects. The spectroscopic observation of mid-gap trap states is linked to the dark current generation dictating the upper performance limits of organic photodiodes

    The application of Evidence-Based Medicine methodologies in sports science: problems and solutions

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    This thesis analyses the use of 'Evidence-Based' methodologies of evidence assessment and intervention and policy design from medicine, and their use in sport and exercise science. It argues that problems exist with the application of Evidence-Based methodologies in sports science, meaning that the quality of evidence used to inform decision-making is lower than is often assumed. This thesis also offers realistic solutions to these problems, broadly arguing for the importance of taking evidence from mechanistic studies seriously, in addition to evidence from RCTs

    The Electrophysiological Effects of Vestibular Stimulation in Parkinson's Disease

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    A recent study showed that vestibular stimulation can produce long-lasting alleviation of motor and non-motor features in Parkinson’s disease (PD). The improvements observed in motor symptoms were of particular note and may provide an indication as to one of the underlying physiological mechanisms of action for vestibular stimulation. An electrophysiological marker known to be abnormal in PD is the Bereitschaftpotential (BP) of the movement-related cortical potentials (MRCPs). One aim of this thesis was to observe the effects of galvanic vestibular stimulation (GVS) on MRCPs in PD to better understand its underlying physiological mechanisms. Many studies measuring the electrophysiological response to GVS have employed pre- versus post-GVS protocols, limiting observations to only after stimulation. The investigation of the mechanisms during GVS is limited by the large artifacts that contaminate the electroencephalograph (EEG). Previous studies have described pre-processing strategies to remove the GVS-related artifact, but these have many limitations. Thus, another aim of this thesis was to describe an artifact removal strategy using a novel approach of employing Independent Components Analysis (ICA) to identify, quantify and eliminate the GVS-related artifact from the EEG data. Study 1 (n = 11) validated this strategy by successfully removing the GVS-related artifact from MRCP data when manipulating the GVS frequency. Study 2 (n = 9) provided further validation by showing successful removal of the GVS-related artifact associated with a higher GVS intensity. Study 3 applied the methodology validated in the first two studies to a PD sample and found a significant increase in the early BP associated with GVS. This suggests that vestibular stimulation may improve motor features in PD through modulation of underlying pathological oscillations associated with motor dysfunction
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