187 research outputs found
Fabrication and characterization of biodegradable poly(3-hydroxybutyrate) composite containing bioglass
No full textBacterially derived poly(3-hydroxybutyrate) (P(3HB)) has been used to produce composite films by incorporating Bioglass particles (<5 m) in 5 and 20 wt % concentrations. P(3HB) was produced using a large scale fermentation technique. The polymer was extracted using the Soxhlet technique and was found to have similar thermal and structural properties to the commercially available P(3HB). The effects of adding Bioglass on the microstructure surface and thermal and mechanical properties were examined using differential scanning calorimetry, dynamic mechanical analysis (DMA), X-ray diffraction, surface interferometry, electron microscopy, and nanoindentation. The addition of increasing concentrations of Bioglass in the polymer matrix reduced the degree of crystallinity of the polymer as well as caused an increase in the glass transition temperature as determined by DMA. The presence of Bioglass particulates reduced the Young's modulus of the composite. The storage modulus and the loss modulus, however, increased with the addition of 20 wt % Bioglass. A short period (28 days) in vitro bioactivity study in simulated body fluid confirmed the bioactivity of the composites, demonstrated by the formation of hydroxyapatite crystals on the composites' surface. <br/
Nanoindentation testing of biodegradabale polymers
No full textNanoindentation testing of biodegradabale polymer
Development of polyhydroxyalkanoates/Bioglass® composite tissue scaffolds for tissue engineering applications
No full text: a point prevalence study
No full textObjectivesOccult (surface antigen-negative/DNA-positive) hepatitis B virus (HBV) infection is common in areas of the world where HBV is endemic. The main objectives of this study were to determine the prevalence of occult HBV infection in HIV-infected African migrants to the UK and to determine factors associated with occult coinfection.MethodsThis anonymized point-prevalence study identified Africans attending three HIV clinics, focussing on patients naïve to antiretroviral therapy (ART). Stored blood samples were tested for HBV DNA. Prevalence was calculated in the entire cohort, as well as in subpopulations. Risk factors for occult HBV coinfection were identified using logistic regression analysis.ResultsAmong 335 HIV-positive African migrants, the prevalence of occult HBV coinfection was 4.5% [95% confidence interval (CI) 2.8–7.4%] overall, and 6.5% (95% CI 3.9–10.6%) and 0.8% (95% CI 0.2–4.6%) in ART-naïve and ART-experienced patients, respectively. Among ART-naïve anti-HBV core (anti-HBc)-positive patients, the prevalence was 16.4% (95% CI 8.3–25.6%). The strongest predictor of occult coinfection was anti-HBc positivity [odds ratio (OR) 7.4; 95% CI 2.0–27.6]. Median HBV DNA and ALT levels were 54 IU/mL [interquartile range (IQR) 33–513 IU/mL] and 22 U/L (IQR 13–27 U/L), respectively.ConclusionsOccult HBV coinfection remains under-diagnosed in African HIV-infected patients in the UK. Given the range of HBV DNA levels observed, further studies are warranted to determine its clinical significance and to guide screening strategies and ART selection in these patients
Effect of silver content on the structure and antibacterial activity of silver-doped phosphate-based glasses
No full textStaphylococcus aureus can cause a range of diseases, such as osteomyelitis, as well as colonize implanted medical devices. In most instances the organism forms biofilms that not only are resistant to the body's defense mechanisms but also display decreased susceptibilities to antibiotics. In the present study, we have examined the effect of increasing silver contents in phosphate-based glasses to prevent the formation of S. aureus biofilms. Silver was found to be an effective bactericidal agent against S. aureus biofilms, and the rate of silver ion release (0.42 to 1.22 µg·mm–2·h–1) from phosphate-based glass was found to account for the variation in its bactericidal effect. Analysis of biofilms by confocal microscopy indicated that they consisted of an upper layer of viable bacteria together with a layer (20 µm) of nonviable cells on the glass surface. Our results showed that regardless of the silver contents in these glasses (10, 15, or 20 mol%) the silver exists in its +1 oxidation state, which is known to be a highly effective bactericidal agent compared to that of silver in other oxidation states (+2 or +3). Analysis of the glasses by 31P nuclear magnetic resonance imaging and high-energy X-ray diffraction showed that it is the structural rearrangement of the phosphate network that is responsible for the variation in silver ion release and the associated bactericidal effectiveness. Thus, an understanding of the glass structure is important in interpreting the in vitro data and also has important clinical implications for the potential use of the phosphate-based glasses in orthopedic applications to deliver silver ions to combat S. aureus biofilm infections
The effects of combined action observation and motor imagery on corticospinal excitability and movement outcomes: Two meta-analyses
No full textSamantha Chye and Ashika Chembila Valappil are shared first authors for this manuscript.Data availability:
The research data/code used for this meta-analysis can be accessed via the Open Science Framework: https://osf.io/4wtqp/?view_only=ff0f008f561a459d8619543cc96e7efd . Supplementary material is available online at https://www.sciencedirect.com/science/article/pii/S0149763422004006#sec0265 .Copyright © 2022 The Author(s). Motor simulation interventions involving motor imagery (MI) and action observation (AO) have received considerable interest in the behavioral sciences. A growing body of research has focused on using AO and MI simultaneously, termed ‘combined action observation and motor imagery’ (AOMI). The current paper includes two meta-analyses that quantify changes in corticospinal excitability and motor skill performance for AOMI compared to AO, MI and control conditions. Specifically, the first meta-analysis collated and synthesized existing motor evoked potential (MEP) amplitude data from transcranial magnetic stimulation studies and the second meta-analysis collated and synthesized existing movement outcome data from behavioral studies. AOMI had a positive effect compared to control and AO but not MI conditions for both MEP amplitudes and movement outcomes. No methodological factors moderated the effects of AOMI, indicating a robust effect of AOMI across the two outcome variables. The results of the meta-analyses are discussed in relation to existing literature on motor simulation and skill acquisition, before providing viable directions for future research on this topic.This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors
Design Optimization of Shock Mounts Subjected to an Underwater Blast Wave
No full textShock mounts are crucial components in reducing the transmissibility of a shock or impact, thereby protecting the objective system. Such shock mounts are application-specific and need a redesign for specific uses. This study establishes a transient nonlinear finite element optimization procedure to design a shock mount for withstanding an underwater blast wave. The work showcases the analysis of two design concepts. The first design demonstrates average acceleration transmissibility of 5.51e-3. The second design exploits the phenomenon of reflection of waves at an interface. This design is unique, promising a factor 3.263 lower average transmissibility than the first design which is similar without the metal interface. The study also details the modeling and analysis of both shock mount designs using 2D axisymmetric and 3D transient nonlinear finite element analyses. The results of both these analyses were comparable, making a 2D study efficient and reliable in the analysis and optimization of shock mounts.Mechanical Engineering | Precision and Microsystems Engineerin
Environmental and Economic Implications of Small-Scale Canadian Aquaponics: A Life Cycle Study
No full textAgricultural production will be challenged in the near future to keep up with the rising nutritional demands of a growing global population. Additionally, climate change, through increased frequency of extreme weather events and droughts, will further push food production to its limits. Controlled-environment food production systems (CEFPS) are suggested as viable options to supplement existing agriculture by allowing food production expansion without requiring large amounts of land and by offering protection from changing weather patterns and other undesirable external conditions. Aquaponics is a form of CEFPS that combines recirculating aquaculture with hydroponics to produce both fish and vegetables. However, the environmental and economic performances of these systems in Canada and other cold climates have yet to be explored in depth. The overarching goal was to evaluate the potential for aquaponics to be a responsible and sustainable solution to maintaining Canadian food security. Specifically, this thesis aimed to identify environmental and economic barriers faced by small-scale Canadian aquaponics systems and provide options for reducing barriers and environmental impacts through the application of life cycle assessment (LCA) and life cycle cost (LCC) analysis. The major results of this study indicate that aquaponics in its current form is an energy-intensive form of agriculture and is more environmentally impactful than conventional forms of fish and vegetable production with a global warming potential (GWP) of 68 kg CO2eq/kg live fish and 50 kg CO2eq/kg leafy greens. Alternative scenarios, including energy efficiency improvements, renewable energy sources, and insect-based fish feed, were considered in order to address the environmental and economic hotspots identified. The following specific conclusions can be made: (1) energy consumption for artificial lighting and heating made necessary by cold climates is the biggest contributor to environmental impacts and costs; (2) an alternative scenario with off-site wind energy, LED lighting, and insulation reduces life cycle costs by 5% and GWP by 97%; and (3) alternative scenarios with insect-feed and on-site renewable energy can reduce specific environmental impacts but are more costly. It is recommended to pay particular attention to building design aspects, such as access to natural lighting and energy efficient HVAC systems, and climate-specific choices, such as cold-resistant crops and fish, in order to reduce the inherent energy intensity of operation. Overall, this work will help researchers and businesses improve performance of aquaponics systems, while serving as a foundation for the sustainability assessment of cold-climate aquaponics
Phononic crystals for suppressing crosstalk in ultrasonic flowmeters
No full textUltrasonic flowmeters that use transit-time ultrasonic transducers face measurement errors due to 'crosstalk,' whereby the working signal travels through the pipe wall and couplings, interfering with the signal from the fluid. Although various procedures have been proposed to solve the issue of crosstalk, they're limited to low-frequency ranges, or they are not effective in high-pressure environments. We propose a mounting mechanism based on a single-phase 3-D phononic crystal (PnC) waveguide that can mitigate crosstalk at high frequencies (megahertz range) and thus improve the flowmeters' measurement accuracy. PnCs are artificial materials consisting of periodically arranged scatterers thereby showing bandgaps (BGs) - ranges of frequencies where elastic/acoustic waves are attenuated - due to Bragg scattering. We design PnC wave filters by engineering the BG frequency range to the working signal of the ultrasonic flowmeter. We then fabricate the waveguide using additive manufacturing and connect it between the transducer and the pipe wall. Transient ultrasonic experiments show that transducers with PnC mountings attain a 40 dB crosstalk reduction in comparison with a standard transducer mounting configuration.Computational Design and Mechanic
Multi-objective design of 3D phononic crystal waveguide by design space trimming
No full textUltrasonic flowmeters face unique challenges since, in addition to withstanding high fluid pressures, they have to avoid crosstalk, which is the interaction of the signals traveling through the fluid and the solid pipe. To avoid the crosstalk, which leads to poor accuracy or complete loss of the required signal, we develop a mounting mechanism based on phononic crystals (PnCs), which are artificial periodic materials possessing band gaps (BGs) due to Bragg scattering. These PnC structures should also possess high mechanical strength to sustain the fluid pressure. Designing PnCs for such applications is challenging as the BG width and the resistance to mechanical loading are conflicting objectives. To circumvent this, we propose a step-by-step design procedure to optimize both mechanical strength and wave attenuation performance of a single-phase 3D PnC waveguide using parametric sweeping and sensitivity analysis. We use finite element analysis (FEA) to characterize the behavior of the periodic unit cell and the waveguide. Since accurate dynamic FEA at high frequencies is computationally demanding, we develop surrogate models at different levels of the design process. We also consider additive manufacturing aspects in the design procedure, which we validate by 3D-printing the final design and measuring the parameters via computer tomography.Computational Design and Mechanic
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