15,849 research outputs found

    Iron oxide and water paste rheology and its effect on low adhesion in the wheel/rail interface

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    The “wet-rail” phenomenon results in low adhesion between wheel and rail throughout the year, occurring transiently on a slightly wet, or drying railhead. It has been previously proposed that it is caused by a mixture of iron oxides and small amounts of water (from dew or precipitation) on the railhead that form a friction reducing paste. This paper outlines a novel combination of rheology, modelling and experimental work using a twin disc test rig to determine how the rheology of this iron oxide paste affects adhesion. The yield strength of different types of iron oxides, along with solid oxide fraction of the friction reducing paste, was assessed and used as an input into an “adhesion model” for assessing water and oxide suspensions. The rheological and modelling results were compared against very low adhesion recorded in twin disc experimental validation when simulating the wet-rail phenomenon

    RELATIONSHIP BETWEEN BODY-SEAT INTERFACE PRESSURE AND DISCOMFORT DURING ROWING

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    Discomfort and pressure-related tissue injury to the buttocks are common complaints among rowers. The soft tissues of the buttocks are non-uniformly loaded during rowing. The current state of literature on seating discomfort is inconclusive as to a desirable body-seat interface pressure pattern. The purpose of this study was to determine whether localising pressure under bony protuberances or diffusing pressure over soft tissues would result in the least amount of discomfort. Force sensing arrays were used to measure body-seat interface pressures in 11 elite female rowers during rowing. Peak pressure measures were identified and pressure gradients were calculated. Discomfort was quantified using a questionnaire, and pressure data were then correlated with discomfort scores.Discomfort was weakly correlated with each of maximal pressure gradient (r=0.45) and peak pressure (r=0.43). The findings indicate pressure should be redistributed in order to avoid concentrating pressure under the bony protuberances o f the buttocks

    Anytime algorithms for ROBDD symmetry detection and approximation

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    Reduced Ordered Binary Decision Diagrams (ROBDDs) provide a dense and memory efficient representation of Boolean functions. When ROBDDs are applied in logic synthesis, the problem arises of detecting both classical and generalised symmetries. State-of-the-art in symmetry detection is represented by Mishchenko's algorithm. Mishchenko showed how to detect symmetries in ROBDDs without the need for checking equivalence of all co-factor pairs. This work resulted in a practical algorithm for detecting all classical symmetries in an ROBDD in O(|G|³) set operations where |G| is the number of nodes in the ROBDD. Mishchenko and his colleagues subsequently extended the algorithm to find generalised symmetries. The extended algorithm retains the same asymptotic complexity for each type of generalised symmetry. Both the classical and generalised symmetry detection algorithms are monolithic in the sense that they only return a meaningful answer when they are left to run to completion. In this thesis we present efficient anytime algorithms for detecting both classical and generalised symmetries, that output pairs of symmetric variables until a prescribed time bound is exceeded. These anytime algorithms are complete in that given sufficient time they are guaranteed to find all symmetric pairs. Theoretically these algorithms reside in O(n³+n|G|+|G|³) and O(n³+n²|G|+|G|³) respectively, where n is the number of variables, so that in practice the advantage of anytime generality is not gained at the expense of efficiency. In fact, the anytime approach requires only very modest data structure support and offers unique opportunities for optimisation so the resulting algorithms are very efficient. The thesis continues by considering another class of anytime algorithms for ROBDDs that is motivated by the dearth of work on approximating ROBDDs. The need for approximation arises because many ROBDD operations result in an ROBDD whose size is quadratic in the size of the inputs. Furthermore, if ROBDDs are used in abstract interpretation, the running time of the analysis is related not only to the complexity of the individual ROBDD operations but also the number of operations applied. The number of operations is, in turn, constrained by the number of times a Boolean function can be weakened before stability is achieved. This thesis proposes a widening that can be used to both constrain the size of an ROBDD and also ensure that the number of times that it is weakened is bounded by some given constant. The widening can be used to either systematically approximate an ROBDD from above (i.e. derive a weaker function) or below (i.e. infer a stronger function). The thesis also considers how randomised techniques may be deployed to improve the speed of computing an approximation by avoiding potentially expensive ROBDD manipulation

    Effects of a prophylactic knee sleeve on anterior cruciate ligament and lower extremity biomechanics: an examination using musculoskeletal simulation

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    The current study aimed using a two-experiment musculoskeletal simulation-based approach, measuring ACL biomechanics, knee joint kinematics and lower extremity joint loading to examine the effects of both a prophylactic knee sleeve on 1. a sport specific change of direction movement in female footballers and 2. a single leg landing in male footballers. Experiment 1 examined 12 female university first team level footballers (age 20.2 ± 1.34 years, height 1.61 ± 0.06 m, body mass 57.2 ± 5.6 kg) undertaking a 45° cutting movement in sleeve and no-sleeve conditions. Experiment 2 examined 10 male university first team level footballers (age 21.1 ± 1.13 years, height 1.77 ± 0.1 m, body mass 71.9 ± 8.6 kg) undertaking a single leg drop jump landing in sleeve and no-sleeve conditions. In each experiment, data was collected in a biomechanics laboratory and three-dimensional motion capture and ground reaction force information was collected. Three-dimensional kinematics, three-dimensional knee kinetics and ACL ligament forces/ strains were measured using musculoskeletal simulation, and participants were also asked to subjectively rate the knee sleeve in terms of both comfort and stability. Experiment 1 showed that the sleeve condition was associated with greater ACL strain (sleeve = 13.57% and no-sleeve = 10.26%) and forces (sleeve = 1.19BW and no-sleeve = 0.94BW). In addition, the brace condition also enhanced lateral compressive tibiofemoral (sleeve = 4.70BW and no-sleeve = 4.20BW) and total compressive tibiofemoral force (sleeve = 11.73BW and no-sleeve = 11.08BW). Finally, for the subjective ratings, participants indicated that the knee sleeve significantly improved perceived comfort and stability. Experiment 2 did not reveal and statistical differences between knee sleeve and no-sleeve conditions, nor any effects of the knee sleeve on subjective ratings of comfort or stability. Therefore, the findings from the current investigation suggest that the prophylactic knee sleeve examined in the current investigation does not appear to reduce the biomechanical parameters linked to the aetiology of knee pathologies in male/ female footballers

    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

    Changes in friction of zinc flake coated threaded fasteners due to humidity, temperature and storage duration

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    The friction coefficient of a specific material combination is often assumed to be invariant, even in manufacturing processes, such as during the tightening of threaded fastener joints. This paper considers the impact of storage conditions on threaded fastener friction. Fasteners were stored in hot humid and sub-zero temperature conditions to study friction in the thread and underhead contacts. Four Zn-flake coatings, commonly used in the automotive industry were considered. Consequent tightening of these fasteners at room temperature revealed that storage history had a significant impact on their friction coefficients, halving under-head friction in some cases. This varied behaviour was considered to be a response to coating nano-hardness and structure and differences in adsorption/absorption of water and zinc-oxide formation during storage

    Vagus Nerve Stimulation in Medically- Resistant Epilepsy: Efficacy and Tolerance

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    Background: Epilepsy is a common neurological disease that affects 1% of the population. One third of patients with epilepsy will not respond to antiseizure medications. The most effective treatment when a patient has medically resistant epilepsy is epilepsy surgery. Unfortunately, in many cases surgery is not possible. Neuromodulation is a therapy used in those patients and Vagus Nerve Stimulation (VNS) is the most common type. There are many studies focusing on seizure reduction using VNS, it is still unclear which patients will obtain the greatest benefits. Objective: To define the seizure response post-VNS implantation, to determine predictive factors associated with good outcomes after VNS implantation and to evaluate complications and side effects. Analysis will be completed in the total sample of VNS cases, in the paediatric subgroup, in medically resistant generalized epilepsy and pregnant women implanted with VNS. Patients & Methods: Patients with medically resistant epilepsy implanted with VNS at the London Health Science Centre-Western University, from 1997 to July 2018. Results: 1) VNS in epilepsy: 114 patients were included. Median seizure rate reduction was - 67.8% and 55.6% (n=41) had a ≥50% seizure reduction. There was a reduction of hospitalization after VNS implantation from 89.5% (n=102) to 45.6% (n=52). 5.3% (n=6) developed side effects associated with the implantation; and side effects were reported in 63.2% (n=72). 2) Paediatric Group: 22 patients were included. The median age when the VNS was implanted was 13. A ≥50% seizure reduction was achieved in 50% (n=11) and the median seizure reduction was -75%. Side effects were detected in 54.5% (n=12). 3) 46 patients were included in this study with a history of medically resistant generalized epilepsy. The mean age at implantation was 24 years-old. Of the LGS group 41.7% (n=12) of patients had an overall seizure reduction of ≥50%, and in the GGE group 64.7% (n=11) had a seizure reduction of ≥50%. There was a significant reduction of seizure-related hospital admissions. 4) Four patients and seven pregnancies were included. The median duration since implantation was 3.17 years. Three required c-sections, one related to failure to progress, the second due to pre-eclampsia and the third due to breach presentation. All babies were healthy, except one with developmental delay of unclear severity. Conclusion: 1) VNS can reduce the number of seizures by 50% in more than half of the patients implanted. VNS has shown a reduction in hospitalization. It is a safe therapy with frequent mild side effects. 2) The paediatric population obtained similar results compared to the total sample. 3) VNS should be considered as a treatment in patients with therapy resistant generalized epilepsy, especially in cases with GGE. 4) Our small sample suggests VNS is a relatively safe therapy during pregnancy, however, larger sample series should be collected

    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
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