1,958 research outputs found

    On Time-Resolved 3D-Tracking of Elastic Waves in Microscale Mechanical Metamaterials

    Get PDF

    Southern Adventist University Undergraduate Catalog 2023-2024

    Get PDF
    Southern Adventist University\u27s undergraduate catalog for the academic year 2023-2024.https://knowledge.e.southern.edu/undergrad_catalog/1123/thumbnail.jp

    Towards predicting and tailoring properties of energetic materials

    Get PDF
    The field of energetic materials (EMs) involves the study of materials (explosives, propellants, and pyrotechnics) that can release a significant amount of energy when initiated. This property renders EMs particularly useful to a wide array of industries including space travel (rocket propellants), mining (demolition charges), and defence applications. The propensity to release a significant amount of energy upon initiation means these materials are inherently dangerous, as such they are subjected to stringent safety requirements, and must be rigorously characterised prior to use. The safety of an EM is often quantified through the evaluation of the sensitivity (propensity to initiate) with respect to different stimuli such as impact, shock, friction, and electric spark. The focus of this work is the impact sensitivity, a solid-state property which can be influenced through changes in the orientation of molecules in 3D space (polymorphism or co-crystallisation) as well as through changing the structure or bonding environment of the molecules comprising the material. Prediction of this metric has been shown in previous work within the group to be computationally achievable for molecular EMs if the crystal structure of the material is known. This is completed through use of the vibrational up-pumping methodology. Vibrational up-pumping refers to the process by which mechanical impact energy excites delocalised low energy motions in a material and is subsequently channelled upwards into localised molecular vibrations. The vibrational states excited through up-pumping are termed the two-phonon density of states, which represents a measure of how efficiently the initial energy can become trapped on the molecular vibrations. Projection of the twophonon density of states onto the underlying vibrational character yields the up-pumped density which shows a correlation with experimental impact sensitivity. To this date, this method has been applied exclusively to molecular EMs, successfully reproducing experimental sensitivities. While important, focusing on solely molecular materials overlooks those of growing importance such as co-crystals, salts and coordination polymers. Application of the vibrational up-pumping methodology to materials from these areas of growing interest forms the backbone for the work presented in this thesis. Chapter 2 addresses a number of areas within the vibrational up-pumping methodology that could be improved upon, namely, the generation of consistent phonon density of states (g(w)) spectra as well as partial g(w) spectra, the determination of the location of uppermost phonon frequency (Wmax) and the interrogation of vibrational modes within the solid-state vibrations to track the local modes of vibration (bond stretches and angle bends). Three Python scripts have been developed to address these problems and improve the efficiency and applicability of the process by which the impact sensitivity of an EM is predicted via the vibrational up-pumping methodology. Chapter 3 focuses on two unexpected findings that had recently come to light in the EMs group at Edinburgh: a co-crystal of FOX-7 with the non-energetic p-phenylenediamine (PPD) that appeared to be more hazardous to mechanical impact than the pure EM, and a new high-pressure polymorph of 3,4,5-trinitro-1H-pyrazole (TNP) that was markedly more sensitive to initiation than the ambient pressure polymorph. For the former study, strong hydrogen bonding interactions significantly altered the molecular conformation of FOX- 7. For the latter, the molecular conformation remained unchanged in the ambient and high-pressure polymorphs, meaning that crystal packing or pressure-induced vibrational mode hardening must account for the increase in mechanical sensitivity. Taken together both studies present challenges for the up-pumping model, which if successful would allow important structure/property connections to be made. Chapter 4 focuses on salt coordination polymers, all of which present as exceptionally sensitive EMs. The study began with lead azide (LA), which is often used in small quantities as a detonator for a much larger mass of a less sensitive EM. It is well documented that lead has drastic adverse effects to both people and the environment and as such REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) has issued a ban on the use of LA. This has necessitated the development of a number of ‘green’ copper-containing replacements (DBX-1, DBX-2, DBX-3 and Cu(ADNP)) with comparable impact sensitivity and detonation characteristics such that they could potentially be used as drop-in replacements. This type of EM has not been studied before using the vibrational up-pumping procedure; they present a number of unique challenges, exemplified primarily by the need to separate the lattice modes from the molecular modes, which is a key requirement of the vibrational up-pumping model. In this chapter a full discussion on a range of mechanochemical models are investigated, from simple phonon heating, through to up-pumping and consideration of target (i.e. trigger mode) activation. Culminating in the development of a workflow for the treatment of such materials in the future within the vibrational up-pumping methodology. In Chapter 5 the emphasis switches towards applying the up-pumping model in a wider capacity to explore the effects of molecular structure on the impact sensitivity of molecular energetics. Here, the investigation centred on a series of chemically related EMs from three common families, namely pyrazoles, tetrazoles and nitrate esters. A number of these materials only differ by the location or substitution of a single functional group, and yet taken together cover a wide range of impact sensitivity response. Successful predictions of their respective impact sensitivities by the up-pumping model would therefore present a unique opportunity to fully explore structure/property relationships, with molecular flexibility, functional group identity and proximity being key structural features to explore. The data set also allowed further exploration of the trigger mode activation introduced in Chapter 4, where only the weakest bonds in the molecules are vibrationally excited by up-pumping. This approach improves the physical basis for impact sensitivity prediction. Collectively, this thesis explores the application of the vibrational up-pumping methodology to various EMs that present with greater structural complexity than the single-component molecular materials that it was initially designed to model. This work has been aided by the development of supplementary Python scripts which attempt to improve both the efficiency and applicability of the vibrational up-pumping methodology. If successful this work will act to considerably validate vibrational up-pumping, as well as to provide the opportunity to explore in-depth structure/property relationships, to understand the physical basis of impact sensitivity. Such understanding may lead to the development of tailored EMs with desired physical properties in the future

    Adaptations in physiological and neuronal function during diet-induced obesity

    Get PDF
    Obesity significantly increases the risk of developing chronic conditions including type II diabetes, cardiovascular disease, and some cancers. The rate of obesity has tripled globally since 1975, which is in part due to the sudden prevalence and overconsumption of palatable high-fat diets (HFDs). Obesity profoundly perturbs the neural control of energy balance, affecting diverse cell types within the hypothalamus. However, an incomplete understanding of how HFD impacts the regulation of energy balance hinders our ability to more effectively treat obesity. In this thesis, I describe the physiological and neuronal response to HFD feeding in rodents. We identified that HFD exposure elevates the body weight set point, which is initially driven by a transient hyperphagia. This hyperphagia coincides with increased excitatory transmission to lateral hypothalamic orexin (ORX) neurons, which regulate acute food intake. This suggests that ORX neurons may be involved in the initial hyperphagia, implicating them in the development of obesity. As HFD prolongs, body weight gain slows and reaches a new steady state regardless of age at the start, duration of feeding, or palatability of the diet. This sustained weight coincides with increased synaptic contacts to melanin-concentrating hormone (MCH) neurons, which promote weight gain and food intake, likely contributing to the maintenance of obesity. The molecular mechanism underlying the establishment of a new set point remains elusive. During HFD feeding, the presence of a chronic low-grade hypothalamic inflammation exacerbates weight gain, therefore we reasoned that inflammatory factors could modulate appetite-promoting neurons to maintain a new set point. We found that the inflammatory mediator prostaglandin E2 (PGE2) activate MCH neurons via its EP2 receptor (EP2R). Suppressing PGE2-EP2R on MCH neurons partially protects against excess weight gain and fat accumulation in the liver during HFD feeding. This mechanism could contribute to the maintenance of an elevated body weight set point in during diet-induced obesity. Without long-term treatment options in face of the increasing rates of obesity, we are in desperate need of novel interventions. In the future, we hope that targeting EP2R on MCH neurons can lower body weight set point and aid in combatting obesity

    Internal load modelling of tapered-roller main bearings in wind turbines

    Get PDF
    The replacement of double-row spherical roller bearings with double-row tapered roller bearings as the main shaft support in wind turbines has been proposed as one of the solutions to the premature failures affecting the industry. In order to improve our scientific knowledge of tapered roller bearing loading in wind turbine main shafts, this thesis sets out to explore how these components may be modelled, how such models can be utilised to improve the understanding of their operational characteristics in relation to the inflow wind, and to compare their behaviour with that of spherical roller bearings. Novel drivetrain models with tapered roller main bearings are developed in this thesis with capabilities of evaluating internal component loading while accounting for variations in system sti↔ness at different operating points. The findings demonstrate that modelling the moment reaction behaviour of tapered-roller bearings is crucial for even simplistic representations, since moment loads at the wind turbine hub are key drivers of bearing displacement. The models developed here are used in an extensive analysis to determine characteristics and sensitivities regarding operational conditions experienced by double-row tapered roller bearings under realistic turbulent inflow conditions, while properly accounting for the system load-response behaviour, roller load distributions and impacts on bearing fatigue life ratings. The presence of “looped” loading structures and evidence of consistent roller edge-loading throughout normal operation is demonstrated, and load response was also found to be largely shared between the two roller rows, this contrasts strongly with the conditions known to hold for spherical-roller main bearings. High levels of fatigue life sensitivity to both operational and lubrication conditions are documented, and shear effects in the wind were found to have opposite effects depending on the bearing type in use, with increased shear exponents drastically reducing the fatigue life rating of the tapered roller bearing. Crucially, this work demonstrates the uniqueness of load conditions experienced by tapered roller bearings in wind turbines, indicating that experience developed in more conventional rolling bearing applications should not be reapplied blindly without first determining its validity in this application space.The replacement of double-row spherical roller bearings with double-row tapered roller bearings as the main shaft support in wind turbines has been proposed as one of the solutions to the premature failures affecting the industry. In order to improve our scientific knowledge of tapered roller bearing loading in wind turbine main shafts, this thesis sets out to explore how these components may be modelled, how such models can be utilised to improve the understanding of their operational characteristics in relation to the inflow wind, and to compare their behaviour with that of spherical roller bearings. Novel drivetrain models with tapered roller main bearings are developed in this thesis with capabilities of evaluating internal component loading while accounting for variations in system sti↔ness at different operating points. The findings demonstrate that modelling the moment reaction behaviour of tapered-roller bearings is crucial for even simplistic representations, since moment loads at the wind turbine hub are key drivers of bearing displacement. The models developed here are used in an extensive analysis to determine characteristics and sensitivities regarding operational conditions experienced by double-row tapered roller bearings under realistic turbulent inflow conditions, while properly accounting for the system load-response behaviour, roller load distributions and impacts on bearing fatigue life ratings. The presence of “looped” loading structures and evidence of consistent roller edge-loading throughout normal operation is demonstrated, and load response was also found to be largely shared between the two roller rows, this contrasts strongly with the conditions known to hold for spherical-roller main bearings. High levels of fatigue life sensitivity to both operational and lubrication conditions are documented, and shear effects in the wind were found to have opposite effects depending on the bearing type in use, with increased shear exponents drastically reducing the fatigue life rating of the tapered roller bearing. Crucially, this work demonstrates the uniqueness of load conditions experienced by tapered roller bearings in wind turbines, indicating that experience developed in more conventional rolling bearing applications should not be reapplied blindly without first determining its validity in this application space

    Microcircuit structures of inhibitory connectivity in the rat parahippocampal gyrus

    Get PDF
    Komplexe Berechnungen im Gehirn werden durch das Zusammenspiel von exzitatorischen und hemmenden Neuronen in lokalen Netzwerken ermöglicht. In kortikalen Netzwerken, wird davon ausgegangen, dass hemmende Neurone, besonders Parvalbumin positive Korbzellen, ein „blanket of inhibition” generieren. Dieser Sichtpunkt wurde vor kurzem durch Befunde strukturierter Inhibition infrage gestellt, jedoch ist die Organisation solcher KonnektivitĂ€t noch unklar. In dieser Dissertation, prĂ€sentiere ich die Ergebnisse unserer Studie Parvabumin positiver Korbzellen, in Schichten II / III des entorhinalen Kortexes und PrĂ€subiculums der Ratte. Im entorhinalen Kortex haben wir dorsale und ventrale Korbzellen beschrieben und festgestellt, dass diese morphologisch und physiologisch Ă€hnlich, jedoch in ihrer KonnektivitĂ€t zu Prinzipalzellen dorsal stĂ€rker als ventral verbunden sind. Dieser Unterschied korreliert mit VerĂ€nderungen der Gitterzellenphysiologie. Ähnlich zeige ich im PrĂ€subiculum, dass inhibitorische KonnektivitĂ€t eine essenzielle Rolle im lokalen Netzwerk spielt. Hemmung im PrĂ€subiculum ist deutlich spĂ€rlicher ist als im entorhinalen Kortex, was ein unterschiedliches Prinzip der Netzwerkorganisation suggeriert. Um diesen Unterschied zu studieren, haben wir Morphologie und Netzwerkeigenschaften PrĂ€subiculĂ€rer Korbzellen analysiert. Prinzipalzellen werden ĂŒber ein vorherrschendes reziprokes Motif gehemmt die durch die polarisierte Struktur der Korbzellaxone ermöglicht wird. Unsere Netzwerksimulationen zeigen, dass eine polarisierte Inhibition Kopfrichtungs-Tuning verbessert. Insgesamt zeigen diese Ergebnisse, dass inhibitorische KonnektivitĂ€t, funktioneller Anforderungen der lokalen Netzwerke zur Folge, unterschiedlich strukturiert sein kann. Letztlich stelle ich die Hypothese auf, dass fĂŒr lokale inhibitorische KonnektivitĂ€t eine Abweichung von „blanket of inhibition― zur „maßgeschneiderten― Inhibition zur Lösung spezifischer computationeller Probleme vorteilhaft sein kann.Local microcircuits in the brain mediate complex computations through the interplay of excitatory and inhibitory neurons. It is generally assumed that fast-spiking parvalbumin basket cells, mediate a non-selective -blanket of inhibition-. This view has been recently challenged by reports structured inhibitory connectivity, but it’s precise organization and relevance remain unresolved. In this thesis, I present the results of our studies examining the properties of fast-spiking parvalbumin basket cells in the superficial medial entorhinal cortex and presubiculum of the rat. Characterizing these interneurons in the dorsal and ventral medial entorhinal cortex, we found basket cells of the two subregions are more likely to be connected to principal cells in the dorsal compared to the ventral region. This difference is correlated with changes in grid physiology. Our findings further indicated that inhibitory connectivity is essential for local computation in the presubiculum. Interestingly though, we found that in this region, local inhibition is lower than in the medial entorhinal cortex, suggesting a different microcircuit organizational principle. To study this difference, we analyzed the properties of fast-spiking basket cells in the presubiculum and found a characteristic spatially organized connectivity principle, facilitated by the polarized axons of the presubicular fast-spiking basket cells. Our network simulations showed that such polarized inhibition can improve head direction tuning of principal cells. Overall, our results show that inhibitory connectivity is differently organized in the medial entorhinal cortex and the presubiculum, likely due to functional requirements of the local microcircuit. As a conclusion to the studies presented in this thesis, I hypothesize that a deviation from the blanket of inhibition, towards a region-specific, tailored inhibition can provide solutions to distinct computational problems

    Southern Adventist University Undergraduate Catalog 2022-2023

    Get PDF
    Southern Adventist University\u27s undergraduate catalog for the academic year 2022-2023.https://knowledge.e.southern.edu/undergrad_catalog/1121/thumbnail.jp

    Development of 3D printed enzymatic biofuel cells for powering implantable biomedical devices

    Get PDF
    The drive toward device miniaturisation in the field of enzyme-based bioelectronics established a need for multi-dimensional geometrically structured and highly effective microelectrodes, which are difficult to implement and manufacture in devices such as biofuel cells and sensors. Additive manufacturing coupled with electroless metal plating enables the production of three-dimensional (3D) conductive microarchitectures with high surface area for potential applications in such devices. However, interfacial delamination between the metal layer and the polymer structure is a major reliability concern, which results in device performance degradation and eventually device failure. This thesis demonstrates a method to produce a highly conductive and robust metal layer on a 3D printed polymer microstructure with strong adhesion by introducing an interfacial adhesion layer. Prior to 3D printing, multifunctional acrylate monomers with alkoxysilane (-Si-(OCH3)3) were synthesised via the Thiol-Michael addition reaction between pentaerythritol tetraacrylate (PETA) and 3-mercaptopropyltrimethoxysilane (MPTMS) with a 1:1 stoichiometric ratio. Alkoxysilane functionality remains intact during photopolymerisation in a projection micro-stereolithography (P”SLA) system and is utilised for the sol-gel reaction with MPTMS post-functionalisation of the 3D printed microstructure to build an interfacial adhesion layer. This functionalisation leads to the implementation of abundant thiol functional groups on the surface of the 3D printed microstructure, which can act as a strong binding site for gold during electroless plating to improve interfacial adhesion. The 3D conductive microelectrode prepared by this technique exhibited excellent conductivity of 2.2×107 S/m (53% of bulk gold) with strong adhesion between a gold layer and a polymer structure even after harsh sonication and adhesion tape test, which offers potential to build a robust 3D conductive microarchitecture for applications such as biosensors and biofuel cells. As a proof-of-concept, the microelectrode with gold-coated complex lattice geometry was employed as an enzymatic glucose anode, which showed a significant increase in the current output compared to the one in the simple cube form. As the first approach, glucose oxidase was used as an enzyme. To find the optimal protocol for the enzyme immobilisation, the enzyme was first immobilised on agarose to achieve the enzyme’s highest activity and stability. Then, this immobilisation protocol was applied to immobilise the enzyme on the gold electrode surface. Preliminary studies on the preparation of 3D gold diamond lattice microelectrode modified with cysteamine and glucose oxidase as a bioanode for single cell enzymatic biofuel cell (EFC) application were performed, which demonstrated high current density of 0.38 ÎŒA cm–2 at 0.35 V in glucose solutions. This method for fabrication of 3D conductive microelectrodes offers potential for several biological applications. Instead of using a thiol, the surface of the 3D-printed part can be functionalised with different other functional groups to create an appropriate surface for biomolecules and cell adhesion. Furthermore, the surface of thiol functionalised printed parts can be perfect for additional metal coatings, opening the door to the creation of highly efficient and customised implantable energy harvesters and biosensors

    (b2023 to 2014) The UNBELIEVABLE similarities between the ideas of some people (2006-2016) and my ideas (2002-2008) in physics (quantum mechanics, cosmology), cognitive neuroscience, philosophy of mind, and philosophy (this manuscript would require a REVOLUTION in international academy environment!)

    Get PDF
    (b2023 to 2014) The UNBELIEVABLE similarities between the ideas of some people (2006-2016) and my ideas (2002-2008) in physics (quantum mechanics, cosmology), cognitive neuroscience, philosophy of mind, and philosophy (this manuscript would require a REVOLUTION in international academy environment!
    • 

    corecore