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Models of flow and diffusion: I : Selective withdrawal from a stratified fluid II: Dispersal of hydrogen in the retina
Get PDFThis dissertation is divided into two parts. In the first part we investigate the withdrawal of fluid from a region of fluid with the outlet situated at an arbitrary location. A model for the dispersal of hydrogen released into the retina in an attempt to estimate blood flow in the eye is considered in the second part.
In the first part, the flow induced by a line sink at an arbitrary location in a fluid of finite depth with a free surface, relevant to flows in reservoirs, lakes and cooling ponds, is examined. A rigid-lid solution for small flow rates is obtained and a numerical method based on fundamental singularities techniques is applied to the full nonlinear problem. Both linear and numerical steady solutions are obtained for the shape of the free surface and show good agreement. The results suggest that steady non-linear solutions are limited to flow rates below some critical value that depends on the sink location, the surface tension and the strength of the flow. A theorem has been proven regarding the behaviour of the fluid surface and some interesting surface shapes are obtained.
The two-dimensional steady flow of an inviscid fluid induced by a line sink located at an arbitrary location in a region of infinite depth is computed. The solution in the limit of small Froude number is obtained analytically, and numerically for the nonlinear problem. The asymptotic solution is found to have a property that if the horizontal location of the sink, xs 1 a second stagnation point forms on the free surface. This has implications for the design of outlets in dams and reservoirs. Numerical solution for the nonlinear problem confirms these properties. The effect of moving the sink horizontally has also been considered. The maximum Froude numbers at which steady solutions exist are computed and compared with previous work and the effects of surface tension are investigated.
Finally in this part, we examine the unsteady flow due to a line sink in a fluid of finite depth with surface tension where the sink is situated at an arbitrary depth and location. Here we focus on critical values of flow rate that lead to steady or drawn down surfaces and the transitions between the different cases. A solution to the un-steady, linear problem is derived using an integral equation technique. The unsteady, nonlinear equation is then solved numerically using a novel fundamental singularities method. The shape of the free surface is computed for a range of parameter values where the effects of surface tension are taken into account. The linear solution is shown to be in a good agreement with the full nonlinear solution until the depth becomes significant, at which point the nonlinearities become apparent and the two solutions begin to differ slightly. We will examine the behaviour of the flow when the fluid is stagnant and the sink is turned on suddenly. Initially, the free surface is pulled down everywhere regardless of Froude number, F , and surface tension, β, firstly, either near the wall, if the sink is close to the wall, or above the sink, in cases where the sink is situated further from the origin. If the Froude number, F , is large enough the initial dip will keep going until drawdown occurs. However, if the Froude number, F , is smaller, the central region rebounds upward and that leads to a more complicated situation where there are several possible outcomes. There are three general states at the breakdown point of the simulations. These are, evolution to a steady state, drawdown of the surface and something in between which may include breaking waves or splashes. In particular, we obtained critical drawdown values of F for a range of values of β, sink location, xs, and different layer depths, H.
In the second major part of the thesis, two mathematical models of advection and diffusion of hydrogen within the retina are discussed to assist in interpretation of the “Hydrogen clearance technique” that is used to estimate blood flow. The first model assumes the retina consists of three, well-mixed layers with different thickness, and the second is a two-dimensional model consisting of three regions that represent the layers in the retina. Diffusion between the layers and leakage through the outer edges are considered. Solutions to the governing equations are obtained by employing Fourier series and finite difference methods for the two models, respectively. The effect of important parameters on the hydrogen concentration is examined and discussed, and a formula is derived for the speed of travel of the bolus of hydrogen. The results contribute to understanding the dispersal of hydrogen in the retina and in particular the effect of flow in the vascular retina. It is shown that the predominant features of the process are captured by the simpler model, meaning that the predictions in experiments can be interpreted without detailed simulation
Progressive white matter injury in preclinical dutch cerebral amyloid angiopathy
No full textAutosomal-dominant, Dutch-type cerebral amyloid angiopathy (D-CAA) offers a unique opportunity to develop biomarkers for pre-symptomatic cerebral amyloid angiopathy (CAA). We hypothesized that neuroimaging measures of white matter injury would be present and progressive in D-CAA prior to hemorrhagic lesions or symptomatic hemorrhage. In a longitudinal cohort of D-CAA carriers and non-carriers, we observed divergence of white matter injury measures between D-CAA carriers and non-carriers prior to the appearance of cerebral microbleeds and >14 years before the average age of first symptomatic hemorrhage. These results indicate that white matter disruption measures may be valuable cross-sectional and longitudinal biomarkers of D-CAA progression
Dexamethasone and clinically significant postoperative nausea and vomiting: A prespecified substudy of the randomised perioperative administration of dexamethasone and infection (PADDI) trial
No full textBackground
Clinically significant postoperative nausea and vomiting (PONV) is a patient-reported outcome which reflects patient experience. Although dexamethasone prevents PONV, it is unknown what impact it has on this experience.
Methods
In this prespecified embedded superiority substudy of the randomised Perioperative Administration of Dexamethasone and Infection (PADDI) trial, patients undergoing non-urgent noncardiac surgery received dexamethasone 8 mg or placebo intravenously after induction of anaesthesia, and completed a validated PONV questionnaire. The primary outcome was the incidence of clinically significant PONV on day 1 or day 2 postoperatively. Secondary outcomes included the incidence of clinically significant PONV and severe PONV on days 1 and 2 considered separately.
Results
A total of 1466 participants were included, with 733 patients allocated to the dexamethasone arm and 733 to matched placebo. The primary outcome occurred in 52 patients (7.1%) in the dexamethasone arm and 66 (9%) patients in the placebo arm (relative risk [RR]=0.79; 95% confidence interval [CI], 0.56–1.11; P=0.18). Severe PONV occurred on day 2 in 27 patients (3.9%) in the dexamethasone arm and 47 patients (6.7%) in the placebo arm (RR=0.58; 95% CI, 0.37–0.92; P=0.02; number needed-to-treat (NNT)=36.7; 95% CI, 20–202). In the entire cohort of 8880 PADDI patients, lower nausea scores, less frequent administration of antiemetics, and fewer vomiting events were recorded by patients in the dexamethasone arm up to day 2 after surgery.
Conclusions
Administration of dexamethasone 8 mg i.v. did not influence clinically significant PONV. Dexamethasone administration did, however, decrease the incidence and severity of PONV, and was associated with less frequent administration of antiemetic agents
Finite-time tracking control for nonholonomic wheeled mobile robot using adaptive fast nonsingular terminal sliding mode
Get PDFSystem uncertainties and external disturbances are the major causes of the trajectory tracking performance degradation in nonholonomic wheeled mobile robots (NWMRs). In this article, an adaptive fast nonsingular terminal sliding mode dynamic control (AFNTSMDC) method is proposed to provide enhanced robust and finite-time tracking performance for the NWMR. The proposed AFNTSMDC is a systematic design method based upon both the kinematic and dynamic model of the NWMR. The proposed controller has a simple form without singularity issue in the control input, which makes it practically implementable. The finite-time stability of the proposed tracking-error function is also proved using the Lyapunov function. Finally, circular trajectory tracking experiments are conducted to validate the robustness and convergence rate of the proposed AFNTSMDC scheme in comparison with the existing methods including classic kinematic control, robust sliding mode kinematic control, and conventional sliding mode dynamic control in the presence of uncertainties and external disturbances
Every coin has two sides: Continuous and substantial reduction of ammonia volatilization under the coexistence of microplastics and biochar in an annual observation of rice-wheat rotation system
No full textMicroplastics (MPs) are verified to affect the fate of ammonia (NH3) in agricultural soils. However, the impacts and mechanisms of MPs coupled with biochar (BC), a widely used agricultural conditioner, on NH3 losses are mostly untapped. The aim of this study was to investigate the mechanisms of common MPs (i.e., polyethylene, polyester, and polyacrylonitrile) and straw-derived BC on NH3 volatilization in rice-wheat rotation soils. Results showed that BC alone and MPs with BC (MPs + BC) reduced 5.5 % and 11.2–26.6 % cumulative NH3 volatilization than the control (CK), respectively, in the rice season. The increased nitrate concentration and soil cation exchange capacity were dominant contributors to the reduced soil NH3 volatilization in the rice season. BC and MPs + BC persistently reduced 44.5 % and 60.0–62.6 % NH3 losses than CK in the wheat season as influenced by pH and nitrate concentration. Moreover, BC and MPs + BC increased humic acid-like substances in soil dissolved organic matter by an average of 159.1 and 179.6 % than CK, respectively, in rice and wheat seasons. The increased adsorption of soil ammonium roots and the promotion of crop root growth were the main mechanism of NH3 reduction. Our findings partially revealed the mechanisms of the coexistence of MPs and BC on NH3 mitigation in rice-wheat rotational ecosystems
Advanced microsamples: Current applications and considerations for mass spectrometry-based metabolic phenotyping pipelines
Get PDFMicrosamples are collections usually less than 50 µL, although all devices that we have captured as part of this review do not fit within this definition (as some can perform collections of up to 600 µL); however, they are considered microsamples that can be self-administered. These microsamples have been introduced in pre-clinical, clinical, and research settings to overcome obstacles in sampling via traditional venepuncture. However, venepuncture remains the sampling gold standard for the metabolic phenotyping of blood. This presents several challenges in metabolic phenotyping workflows: accessibility for individuals in rural and remote areas (due to the need for trained personnel), the unamenable nature to frequent sampling protocols in longitudinal research (for its invasive nature), and sample collection difficulty in the young and elderly. Furthermore, venous sample stability may be compromised when the temperate conditions necessary for cold-chain transport are beyond control. Alternatively, research utilising microsamples extends phenotyping possibilities to inborn errors of metabolism, therapeutic drug monitoring, nutrition, as well as sport and anti-doping. Although the application of microsamples in metabolic phenotyping exists, it is still in its infancy, with whole blood being overwhelmingly the primary biofluid collected through the collection method of dried blood spots. Research into the metabolic phenotyping of microsamples is limited; however, with advances in commercially available microsampling devices, common barriers such as volumetric inaccuracies and the ‘haematocrit effect’ in dried blood spot microsampling can be overcome. In this review, we provide an overview of the common uses and workflows for microsampling in metabolic phenotyping research. We discuss the advancements in technologies, highlighting key considerations and remaining knowledge gaps for the employment of microsamples in metabolic phenotyping research. This review supports the translation of research from the ‘bench to the community’
An argument for pandemic risk management using a multidisciplinary One Health approach to governance: an Australian case study
Get PDFThe emergence of SARS-CoV-2 and the subsequent COVID-19 pandemic has resulted in significant global impact. However, COVID-19 is just one of several high-impact infectious diseases that emerged from wildlife and are linked to the human relationship with nature. The rate of emergence of new zoonoses (diseases of animal origin) is increasing, driven by human-induced environmental changes that threaten biodiversity on a global scale. This increase is directly linked to environmental drivers including biodiversity loss, climate change and unsustainable resource extraction. Australia is a biodiversity hotspot and is subject to sustained and significant environmental change, increasing the risk of it being a location for pandemic origin. Moreover, the global integration of markets means that consumption trends in Australia contributes to the risk of disease spill-over in our regional neighbours in Asia-Pacific, and beyond. Despite the clear causal link between anthropogenic pressures on the environment and increasing pandemic risks, Australia’s response to the COVID-19 pandemic, like most of the world, has centred largely on public health strategies, with a clear focus on reactive management. Yet, the span of expertise and evidence relevant to the governance of pandemic risk management is much wider than public health and epidemiology. It involves animal/wildlife health, biosecurity, conservation sciences, social sciences, behavioural psychology, law, policy and economic analyses to name just a few.
The authors are a team of multidisciplinary practitioners and researchers who have worked together to analyse, synthesise, and harmonise the links between pandemic risk management approaches and issues in different disciplines to provide a holistic overview of current practice, and conclude the need for reform in Australia. We discuss the adoption of a comprehensive and interdisciplinary ‘One Health’ approach to pandemic risk management in Australia. A key goal of the One Health approach is to be proactive in countering threats of emerging infectious diseases and zoonoses through a recognition of the interdependence between human, animal, and environmental health. Developing ways to implement a One Health approach to pandemic prevention would not only reduce the risk of future pandemics emerging in or entering Australia, but also provide a model for prevention strategies around the world
The effect of pre-harvest treatment of calcium nitrate and iron chelate on post-harvest quality of apple (Malus domestica Borkh cv. Red Delicious)
No full textEnhancing the nutrition of fruit trees and crops with chemical fertilizers is one of the most important tools to increase production and improve crop quality during the harvest stage. In East Azerbaijan, apples are grown on calcareous soils, and managing tree nutrition is a precursor to increasing fruit yield and post-harvest fruit quality. A factorial experiment was conducted in a completely randomized block design in a Red Delicious apple orchard to investigate whether the application of calcium nitrate (Ca(NO3)2) at 50, 100, and 150 g tree−1 and iron (Fe) chelate (6% Fe) at (10, 20, and 30 mL tree-1) to the soil are beneficial. The fertilizers were applied at three times during fruit development: stage of cell division in young fruit, stage of peak rate of cell expansion and starch accumulation, and stage of cell expansion and the beginning of starch decline. The addition of Ca(NO3)2 and Fe-chelate affected fruit yield and fruit traits in storage, including total carbohydrate, pH, phenol, ripening index (TSS/TA), TSS, TA, fruit firmness, and weight loss. Fertilizer application also altered the concentration of some mineral nutrients in leaves and fruits. There was an interaction between storage time × Ca× Fe on fruit firmness, total carbohydrate, TSS, pH, and TA fruit. Fertilization with Fe-chelate increased fruit Ca and leaf Fe. Overall, the combination of 50 g Ca(NO3)2 and 30 mL Fe-chelate is recommended for apple orchardists in this part of Iran
Doping sodium tungsten Bronze-Like (Na5W14O44) Near-Infrared shielding functional units in bulk borosilicate glasses for Energy-Saving window applications
No full textTungsten bronze is an effective near-infrared (NIR) shielding material for fabricating energy-saving smart windows. While high-performing NIR-shielding glasses can be fabricated by coating a tungsten bronze film on window glasses, these glasses suffer a short lifespan due to the adhesion and degeneration of film. In this work, we show that tungsten bronze-like material Na5W14O44 can be distributed in the bulk glass matrix during the facile melt-quenching glass fabrication process under an air atmosphere, overcoming the limitations of film-based glasses. X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy confirmed the presence of tungsten bronze-like Na5W14O44 functional units in the SiO2–B2O3–NaF glass matrix. The addition of a small amount of H2WO4 and Sb2O3 is critical for the formation of Na5W14O44 functional units because H2WO4 provides W for Na5W14O44, and Sb2O3 acts as a reducing agent that helps the formation of W5+ in Na5W14O44 under an air atmosphere. Furthermore, the NIR-shielding ability can be tuned by adjusting the concentration of Sb2O3 in the range of 0–1.5 mol % and of H2WO4 in the range of 4–6 mol %. The optimized composition containing 1.25 mol % of Sb2O3 and 5 mol % of H2WO4 exhibits excellent NIR-shielding ability (ΔT = 62.8%), high visible light transmittance (Tmax = 67.7%), and excellent thermal insulation. This performance is comparable to cesium tungsten bronze film-based glasses and much better than soda lime glass and ITO glass under sun irradiation. This study sheds light on fabricating energy-saving windows in a simple and cost-effective way with flexibility for fine tuning of NIR-shielding performance
Evaluating conservation strategies for the endangered daisy Schoenia filifolia subsp. subulifolia (Asteraceae): fitness consequences of genetic rescue and hybridisation with a widespread subspecies
Get PDFContext: To establish translocated populations of threatened plants with the genetic resources to adapt to changing environmental conditions, the source of propagation material is an important consideration.
Aim: We investigated the fitness consequences of genetic rescue and admixture for the threatened annual daisy Schoenia filifolia subsp. subulifolia, and the common S. filifolia subsp. filifolia, to inform seed-sourcing strategies for translocations of the threatened subspecies.
Methods: We evaluated genetic diversity of two populations of S. filifolia subsp. subulifolia and four populations of S. filifolia subsp. filifolia by using microsatellite markers. We grew seedlings from each study population and cross-pollinated inflorescences within and among populations of the same subspecies, and between subspecies. We evaluated the fitness consequences of each cross by using seed set, seed weight and seed viability.
Key results: There was a lower genetic diversity in the small (10 000 plants, Nar = 4.42, He = 0.51) population of S. filifolia subsp. subulifolia, although none of the measures was significantly different, and seed fitness was slightly, although not significantly, reduced in interpopulation crosses compared with the small population. Genetic diversity was similar between the threatened and widespread subspecies; however, the subspecies were genetically divergent (Fst = 0.242–0.294) and cross-pollination between subspecies produced negligible amounts of seeds (<3% seed set).
Conclusions: Although genetic rescue or admixture of S. filifolia subsp. subulifolia would not necessarily result in greatly increased levels of genetic diversity or seed fitness, we still consider it a potential option. Negligible seed set in crosses between subspecies indicates that deliberate hybridisation is not a possibility.
Implications: Studies of fitness consequences of admixture or genetic rescue are rare yet critical to assessing the benefits of different translocation strategies