Bifurcations in impact oscillators: theoretical and experimental studies.

One of the most important features of nonlinear dynamicai systems is that, as system parameters are varied, qualitative changes in the overall behaviour of the system can occur at a bifurcation . For smooth systems, the local bifurcations which occur under the change of one parameter are well understood. Non-smooth dynamical systems, which frequently arise due to the way certain physical processes are modelled, undergo bifurcations which have not been widely studied. We examine a particular type of bifurcation arising in a commonly occurring class of non-smooth dynamical system, combining theoretical and experimental results. In this thesis we are concerned with the study of the important class of dynamical system we call impact oscillators, which undergo oscillations under the influence of some forcing, and additionally can undergo impacts at rigid stops. Such systems are of interest because a large number of physical and engineering systems display behaviour which can be classified as impacting, where it is important to use a dynamical analysis to identify and thus avoid the noise, wear or failure which could be caused by repeated impacts producing unacceptably large loads. Recent interest in such systems has concentrated on the unusual bifurcational behaviour which occurs when part of an orbit begins to undergo low velocity impacts. Using analytical methods to locate particular simple steady state solutions of an impact oscillator these grazing bjfurcations are investigated. Comparisons are made between the behaviour of these special bifurcations, which arise because of the instantaneous reversal of velocity in the mathematical model of the impact process, and the standard bifurcations of smooth dynamical systems. An experimental study of an electromagnetically forced metal beam impacting against a stop is used to show that the overall qualitative behaviour displayed by a simple theoretical model is also displayed in a physical impact oscillator. Finally the theoretical studies are related to a particular problem of offshore engineering and it is shown how a very simple model can be used to explain some unusual observed behaviour

Lagoon livelihoods: gender and shell money in Langalanga, Solomon Islands

© 2018, The Author(s). Gender shapes livelihoods through access to resources and the distribution of benefits from economic activities. To work effectively with local people, resource management and community development initiatives should therefore be sensitive to the influence of gender on livelihoods. This paper considers gender in the context of broader social trends around livelihoods and focuses on a case study of shell money production and trade in the Langalanga Lagoon in Malaita Province, Solomon Islands. We pool data from several recent research projects with historical material from secondary sources. We find that the gender division of labour in the shell money value chain has changed somewhat over time, particularly in that women are now actively involved in trading. However, this shift has created friction due to norms about what kinds of activities are suitable for women, and who should control cash incomes. Whilst shell money remains one of the most important livelihoods in Langalanga lagoon, our findings also illustrate that the shell money value chain and the income earned varies considerably from family to family, with some making a better living than others. We argue that interventions seeking to improve livelihoods in coastal communities should thus be based on an understanding of differentiation within communities, and practitioners should consider whether interventions will result in community development, or may have the impact of increasing inequality between families

The natural history of regional wall motion in the acutely infarcted canine ventricle

Two-dimensional echocardiography was employed to define the natural history of regional wall motion abnormalities in a canine model of acute experimental myocardial infarction. Serial short-axis two-dimensional echocardiograms were recorded in 11 closed chest dogs before coronary occlusion and 10, 30, 60, 180 and 360 minutes after permanent coronary ligation. Radiolabeled microsphere-derived blood flows were obtained in each study period and the histochemical (triphenyltetrazolium chloride) extent of infarction was determined at 6 hours. Previously published methods were used to quantitate field by field (every 16.7 ms) excursion of 36 evenly spaced endocardial targets. The circumferential extent of abnormal wall motion was followed sequentially using previously published definitions of abnormality: 1) systolic fractional radial change of less than 20%; 2) dyskinesia (systolic bulging) at the point in time (echocardiographic field) in which there is maximal dyskinesia; and 3) correlation with composite normal ray motion falling outside the 95 % confidence limits defined in the control period. On the basis of the triphenyltet razolium chloride staining pattern, the ventricle was divided into five zones: central infarct zone, zone with greater than 25% transmural infarction, total infarct zone, border zones and normal zone. Mean systolic fractional radial change was calculated for each zone and used as an index of the magnitude of abnormal wall motion.Regardless of the definition of abnormality employed, the circumferential extent of abnormal wall motion manifested at 10 minutes after occlusion did not significantly change, even up to 6 hours later. Similarly, 10 minutes after coronary occlusion the three infarct zones and border zones demonstrated significantly reduced systolic fractional radial change. This remained stable over the remainder of the 6 hour study period.It is concluded that once established at 10 minutes after coronary occlusion, the circumferential extent and magnitude of abnormal wall motion do not significantly change in the immediate postinfarct (6 hour) period

Derivation of a clinical decision-making aid to improve the insertion of clinically indicated peripheral intravenous catheters and promote vessel health preservation. An observational study

Background It is well established that the idle peripheral intravenous catheter (PIVC) provides no therapeutic value and is a clinical, economic and above all, patient concern. This study aimed to develop a decision aid to assist with clinical decision making to promote clinically indicated peripheral intravenous catheter (CIPIVC) insertion in the emergency department (ED) setting. Providing evidence for a uniform process could assist clinicians in a decision-making process for PIVC insertion. This could enable patients receive appropriate vascular access healthcare. Methods We performed a secondary analysis of data from a multicentre cohort of emergency department clinicians who performed PIVC insertion. We defined CIPIVC a priori as one used for a specific clinical treatment and or procedure such as prescribed intravenous (IV) fluids; prescribed IV medication; or IV contrast (for computerized tomography scans). We sought to refute or validate an assumption if the clinician performing or requesting the insertion decided the patient was >80% likely to need a PIVC. Using logistic regression, we derived a decision aid for CIPIVCs. Results In 817 patients undergoing PIVC insertion, we observed 68% of these to be CIPIVCs. Admitted patients were significantly more likely to have a CIPIVC, Odds Ratio (OR) = 3.05, 95% confidence interval (CI) = 2.17–4.30, p = <0.0001. Before insertion, patients who definitely needed IV fluids/medicines OR = 3.30, 95% CI = 2.02–5.39, p = <0.0001 and who definitely needed a contrast scan OR = 3.04, 95% CI = 1.15–8.03, p = 0.0250 were significantly more likely to have a device inserted for a clinical indication. Patients who presented with an existing vascular access device were more likely to have a new CIPIVC inserted for use OR = 4.35, 95% CI = 1.58–11.95, p = 0.0043. The clinician’s pre-procedural judgment of the likelihood of therapeutic use >80% was independently associated with CIPIVC; OR 3.16, 95% CI = 2.06–4.87, p<0.0001. The area under the receiver operating characteristic curve was 0.81, and at the best cut-off, the model had a specificity of 0.81, sensitivity of 0.71, a positive predictive value of 0.89 and negative predictive value of 0.57. Conclusions Using the derived decision aid, clinicians could ask:- “Does this patient need A-PIVC?” Clinicians can decide to insert a CIPIVCs when: (i) Admission to hospital is anticipated and when (ii) a Procedure requires a PIVC, e.g., computerised tomography scans and where an existing suitable vascular access device is not present and or; (iii) there is an indication for IV fluids and or medicines that cannot be tolerated enterally and are suitable for dilution in peripheral veins; and, (iv) the Clinician’s perceived likelihood of use is greater than 80%.Full Tex

Dynamic Analysis of Double Wishbone Front Suspension Systems for Sport Motorcycles

In this paper, two alternative front suspension systems and their influence on motorcycle dynamics are investigated. Based on an existing motorcycle mathematical model, the front end is modified to accommodate both Girder and Hossack suspension systems. Both of them have in common a double wishbone design that varies the front end geometry on certain manoeuvrings and, consequently, the machine’s behaviour. The kinematics of the two systems and their impact on the motorcycle performance is analysed and compared to the well known telescopic fork suspension system. Stability study for both systems is carried out by means of root-loci methods, in which the main oscillation modes, weave and wobble, are studied and compared to the baseline model

The FARMSCAPE approach to farming systems research

Abstract From six years of participatory action research has emerged Farmers&apos;, Advisers&apos; and Researchers&apos; Monitoring, Simulation. Communication And Performance Evaluation (FARMSCAPE) as an approach for supporting farmers&apos; management of dryland crop production. In contrast to the strategy of producing decision support software for farmers, FARMSCAPE features simulation-aided discussions about management among farmers, advisers, and (sometimes) researchers. The key is a capability to flexibly simulate the consequences of a wide range of crop and cropland management alternatives in a variable climate at a paddock scale using local soil and weather data. The high level of interest among farmers has led to a current focus on transfer of the technology to agricultural service providers. Keywords: Farming systems, on-farm, simulation, soil monitoring, action research The term &quot;farming systems research&quot; is most commonly used in Australia to mean &quot;research on bio-physical sub-systems aimed at improving systems of farming&quot;. Research methodology tends to be a flexible and pragmatic use of formal experimental design and statistical analysis. Experiments are designed to represent aspects of farming sufficiently realistically for results to be meaningful to farmers and advisers but without unnecessarily or overly straining professional standards for methodology concerning making valid comparisons with adequate confidence. In the interest of the former, experiments are often located on commercial farms, and, increasingly, with farmers. A second established way of interpreting the term &quot;farming systems research&quot; is &quot;systems research which is about farming&quot;. Here the emphasis is the application to farming of systems concepts and methodologies that have evolved over the past 50 years, mainly outside agriculture. This paradigm has been termed &quot;systems agriculture&quot; (1). Emphasis here is on approaches to learning/ research/ intervention when the system under study does not lend itself readily to scientific experimentation. Feasibility of the latter declines with increases in scale and/or, complexity and temporal variability. Two pools of methodological resources for addressing such systems are available&amp;mdash;often termed &quot;hard&quot; and &quot;soft&quot; approaches. &quot;Hard&quot; systems approaches have, at their core, mathematical models of the systems of interest designed to represent the essential aspects of function in relation to environment. But the hard lesson in the main stream of the hard systems movement has been that the approach turns out to be appropriate only to those aspects of systems that are not complicated by people with purposes and freedom of choice (3). The fact that the specific nature of a farm system substantially reflects the design and management efforts of a farmer means that a &quot;soft&quot; systems approach, eg participative action research, should enhance the usefulness and impact of the research on real farming. McCown, RL; Carberry, PS; Foale, MA; Hochman, Z; Coutts, JA; Dalgliesh, NP (1998) The FARMSCAPE approach to farming systems research Proc. 9th Aust. Agron. Conf., Wagga Wagga (1998) 633-636

Management of Acute Coronary Syndromes During the Coronavirus Disease 2019 Pandemic: Deviations from Guidelines and Pragmatic Considerations for Patients and Healthcare Workers

Coronavirus disease 2019 (COVID-19) is forcing cardiology departments to rapidly adapt existing clinical guidelines to a new reality and this is especially the case for acute coronary syndrome pathways. In this focused review, the authors discuss how COVID-19 is affecting acute cardiology care and propose pragmatic guideline modifications for the diagnosis and management of acute coronary syndrome patients, particularly around the appropriateness of invasive strategies as well as length of hospital stay. The authors also discuss the use of personal protective equipment for healthcare workers in cardiology. Based on shared global experiences and growing peer-reviewed literature, it is possible to put in place modified acute coronary syndrome treatment pathways to offer safe pragmatic decisions to patients and staff

Farmers, advisers and researchers learning together better management of crops and croplands

Summary. Farmers in the northeastern sub-tropics of Australia must cope with very high climatic variability in order to succeed in crop production. Their capacity for innovation was tapped by means of an on-farm research project that brought farmers, advisers and researchers together on the Darling Downs and in central Queensland. The researchers added value to the farmers&apos; own experiments on fertility and water use efficiency by soil and weather monitoring at specific sites and then using a simulation model of cropping systems to extend findings to a wider context of climate and soil. The advisers extended knowledge aquired from this experience via local farmer networks and have undertaken training in the use of simulation to support farmers&apos; management decisions. The experience described opens up possibilities for developing new, cost-effective ways for devising and testing improved farm management