15,017 research outputs found

    Passive control of a bi-ventricular assist device : an experimental and numerical investigation

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    For the last two decades heart disease has been the highest single cause of death for the human population. With an alarming number of patients requiring heart transplant, and donations not able to satisfy the demand, treatment looks to mechanical alternatives. Rotary Ventricular Assist Devices, VADs, are miniature pumps which can be implanted alongside the heart to assist its pumping function. These constant flow devices are smaller, more efficient and promise a longer operational life than more traditional pulsatile VADs. The development of rotary VADs has focused on single pumps assisting the left ventricle only to supply blood for the body. In many patients however, failure of both ventricles demands that an additional pulsatile device be used to support the failing right ventricle. This condition renders them hospital bound while they wait for an unlikely heart donation. Reported attempts to use two rotary pumps to support both ventricles concurrently have warned of inherent haemodynamic instability. Poor balancing of the pumps’ flow rates quickly leads to vascular congestion increasing the risk of oedema and ventricular ‘suckdown’ occluding the inlet to the pump. This thesis introduces a novel Bi-Ventricular Assist Device (BiVAD) configuration where the pump outputs are passively balanced by vascular pressure. The BiVAD consists of two rotary pumps straddling the mechanical passive controller. Fluctuations in vascular pressure induce small deflections within both pumps adjusting their outputs allowing them to maintain arterial pressure. To optimise the passive controller’s interaction with the circulation, the controller’s dynamic response is optimised with a spring, mass, damper arrangement. This two part study presents a comprehensive assessment of the prototype’s ‘viability’ as a support device. Its ‘viability’ was considered based on its sensitivity to pathogenic haemodynamics and the ability of the passive response to maintain healthy circulation. The first part of the study is an experimental investigation where a prototype device was designed and built, and then tested in a pulsatile mock circulation loop. The BiVAD was subjected to a range of haemodynamic imbalances as well as a dynamic analysis to assess the functionality of the mechanical damper. The second part introduces the development of a numerical program to simulate human circulation supported by the passively controlled BiVAD. Both investigations showed that the prototype was able to mimic the native baroreceptor response. Simulating hypertension, poor flow balancing and subsequent ventricular failure during BiVAD support allowed the passive controller’s response to be assessed. Triggered by the resulting pressure imbalance, the controller responded by passively adjusting the VAD outputs in order to maintain healthy arterial pressures. This baroreceptor-like response demonstrated the inherent stability of the auto regulating BiVAD prototype. Simulating pulmonary hypertension in the more observable numerical model, however, revealed a serious issue with the passive response. The subsequent decrease in venous return into the left heart went unnoticed by the passive controller. Meanwhile the coupled nature of the passive response not only decreased RVAD output to reduce pulmonary arterial pressure, but it also increased LVAD output. Consequently, the LVAD increased fluid evacuation from the left ventricle, LV, and so actually accelerated the onset of LV collapse. It was concluded that despite the inherently stable baroreceptor-like response of the passive controller, its lack of sensitivity to venous return made it unviable in its present configuration. The study revealed a number of other important findings. Perhaps the most significant was that the reduced pulse experienced during constant flow support unbalanced the ratio of effective resistances of both vascular circuits. Even during steady rotary support therefore, the resulting ventricle volume imbalance increased the likelihood of suckdown. Additionally, mechanical damping of the passive controller’s response successfully filtered out pressure fluctuations from residual ventricular function. Finally, the importance of recognising inertial contributions to blood flow in the atria and ventricles in a numerical simulation were highlighted. This thesis documents the first attempt to create a fully auto regulated rotary cardiac assist device. Initial results encourage development of an inlet configuration sensitive to low flow such as collapsible inlet cannulae. Combining this with the existing baroreceptor-like response of the passive controller will render a highly stable passively controlled BiVAD configuration. The prototype controller’s passive interaction with the vasculature is a significant step towards a highly stable new generation of artificial heart

    Smart & sustainable cities

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    The University of Strathclyde is creating a new Institute for Future Cities that aims to improve the quality of human life across the world through innovative research that enables cities to be understood in new ways, and innovative approaches to be developed for the way we live, work, learn and invest in cities. The new Institute will create a focus and strategy to coordinate academic research on urban themes, and partnerships with cities, businesses, research institutions and governments across the world. This paper outlines the wider context and issues for urban policy and research, and describes some of the key objectives and activities of the Institute for Future Cities - including the €3.7 million EU FP7 STEP UP project on sustainable city planning and implementation, a new ESRC research programme on crime prediction, and the City Observatory within the £24 million TSB Future City Demonstrator in Glasgow

    Dynamical evolution of star forming regions - II. Basic kinematics

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    We follow the dynamical evolution of young star-forming regions with a wide range of initial conditions and examine how the radial velocity dispersion, σ\sigma, evolves over time. We compare this velocity dispersion to the theoretically expected value for the velocity dispersion if a region were in virial equilibrium, σvir\sigma_{\rm vir} and thus assess the virial state (σ/σvir\sigma / \sigma_{\rm vir}) of these systems. We find that in regions that are initially subvirial, or in global virial equilibrium but subvirial on local scales, the system relaxes to virial equilibrium within several million years, or roughly 25 - 50 crossing times, according to the measured virial ratio. However, the measured velocity dispersion, σ\sigma, appears to be a bad diagnostic of the current virial state of these systems as it suggests that they become supervirial when compared to the velocity dispersion estimated from the virial mass, σvir\sigma_{\rm vir}. We suggest that this discrepancy is caused by the fact that the regions are never fully relaxed, and that the early non-equilibrium evolution is imprinted in the one-dimensional velocity dispersion at these early epochs. If measured early enough (<<2 Myr in our simulations, or \sim20 crossing times), the velocity dispersion can be used to determine whether a region was highly supervirial at birth without the risk of degeneracy. We show that combining σ\sigma, or the ratio of σ\sigma to the interquartile range (IQR) dispersion, with measures of spatial structure, places stronger constraints on the dynamical history of a region than using the velocity dispersion in isolation.Comment: 20 pages, 14 figures, accepted for publication in MNRA

    Comparison of the physical and financial performance of organic dairy farming systems (OF0146)

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    This is the final report from Defra project OF0146 Two different systems of organic milk production were studied during the 1998-2002 period. The systems were established at the IGER Ty Gwyn organic dairy farm during the 1998/99 period. The systems were based either on achieving self-sufficiency in both home-grown forage and concentrate feeds or on the production of home-grown forage and the purchase of concentrate feeds. The data collected included recording the changes in the soil indices, level of crop production, crop quality, level of milk production, milk quality, animal health and herd reproductive performance of the two systems. The main attached report starts with a detailed executive summary. In the modelling work fifty-four different strategies for organic dairy production were evaluated. Performance data from three commercial organic dairy farms with different climatic conditions (Devon, Pembrokeshire and Shropshire) and cropping strategies (arable with all home-grown feed, home-grown forage only, home-grown forage + purchased concentrates) and also data from the two Ty Gwyn systems was inputted into three models (SAC Dairy Systems, SAC FeedByte, IRS OrgPlan) to evaluate the potential performance from different organic systems. The results produced a range of different options and rankings in relation to their potential financial performance and use of resources. The results from the data modelling predicted the best financial performance and utilisation of resources would be achieved by the establishment of an arable system on the Pembrokeshire farm. The lowest financial performance was predicted to be from the establishment of purchased concentrate systems on the Shropshire and Pembrokeshire farms, with the poorest utilisation of resource use indicators from both the establishment of a forage-only system on the Shropshire farm and purchased feed systems on both the Shropshire and Pembrokeshire farms. In relation to financial indicators the modelling work showed little difference between the two Ty Gwyn systems. The financial performance of Ty Gwyn was compared with ten commercial organic dairy farms, monitored during the 1998-2002 period. Of the ten commercial farms, four had been organic for a number of years, three were recently converted and three were in conversion. The net farm income of the Ty Gwyn SS system increased from 1998/99 to 1999/00 to a peak of £25,453 but then declined sharply following a fall in the price paid for organic milk to a loss of -£14,269 in 2001/02. In the Ty Gwyn PC system the net farm income increased to £24,122 in 2000/01 but then fell sharply to a loss of -£4,825 in 2001/02. The peak net farm incomes on the commercial farms were recorded in the 1999/00 period, with either a small loss (<-£50/ha) recorded on the well established farms or a small profit (<£50/ha) on the recently converted farms in 2001/02

    Revenue Sharing and Player Salaries in Major League Baseball

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    This article analyzes how changes made to the revenue sharing agreement in the 2007 Major League Baseball collective bargaining agreement influenced the salaries of position players and pitchers. The tax rates associated with revenue sharing decreased following ratification of the 2007 agreement. Theoretically, these changes should increase players’ marginal revenue product and, therefore, salaries. Results indicate that position players experienced an increase in salary following the 2007 agreement. Pitchers’ salaries also increased, but by a smaller amount. The effect of the 2007 agreement was different throughout the salary distribution for position players, but uniform throughout the distribution for pitchers

    Cycle tourism development in the Peak District National Park, United Kingdom

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    ABSTRACT Protected areas are at the centre of nature-based tourism, which is increasingly popular across the world. As visitor numbers increase, so does awareness of the harmful effects that large crowds may have on both natural resources and individuals’ recreational experience. This volume considers the challenge of transportation to and within natural and protected areas, the improvement of which has already been recognised as having great potential for mitigating the environmental impacts of ecotourism. While several books have focused considerable attention to the management of protected areas in general, little has been said about the specific issue of sustainable transport, an emerging trend that is already reshaping visitation patterns in natural settings. This book provides current knowledge on issues associated with the transportation of visitors in natural and protected areas, and a comprehensive overview of the technical and strategic options available to tackle these issues. It approaches the subject via three main topics: preferences, or the visitors' attitudes towards transportation; practices, where current approaches are assessed through examples and case-studies of successful experiences and methodologies from around the world; and policies, where suggestions and recommendations are put forward for both local scale strategies and broad-scale regulatory action with global relevance. Contributors include academics in the field of natural resource management and tourism, with extensive experience in protected area management and active partnerships with natural park administrations

    Centralized Oversight of the Regulatory State

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    Born out of a Reagan-era desire to minimize regulatory costs, and not fundamentally reconsidered since its inception, the centralized review of agency rulemakings has arguably become the most important institutional feature of the regulatory state. Yet it is a puzzling feature: although centralized review is sometimes justified on the ground it could harmonize the uncoordinated sprawl of the federal bureaucracy, the agency tasked with regulatory review, the Office of Management and Budget (OMB), has never embraced that role. It has instead doggedly clung to its original cost-reduction mission, justifying its function as a check on the federal bureaucracy with reference to the pervasive belief that agencies will systematically over-regulate. This article shows why this belief is wrong. The claim that agencies are systematically biased in favor of regulation finds little support in public choice theory, the political science literature, or elsewhere. In any event, theories predicting rampant over-regulation are no more plausible than alternative theories suggesting that agencies will routinely under regulate. Even if zealous agencies captured by powerful interest groups did characterize the regulatory state, OMB review is a curious and poorly designed counterweight. There is no reason to believe that OMB's location in the Executive Office of the President will inoculate OMB from the pathologies that afflict other agencies, and some reason to think that it will exacerbate them. As a response to these problems, we urge a reconsideration of the foundational role that centralized review should play in our regulatory state, and a revival and re-conceptualization of the neglected principles of harmonization that once ostensibly animated it.

    2018 Census of California Water Transit Services

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    The U.S. Bureau of Transportation Statistics conducts a nationwide census of ferry boat operators for the U.S. Department of Transportation and the collected information is used for statistical purposes. The Caltrans Division of Local Assistance has been asked by the Federal Highway Administration (FHWA) to gather data regarding ferry operations under the Moving Ahead for Progress in the 21st Century Act (MAP-21). MAP-21 includes a new formula program for ferry boats and ferry terminal facilities eligible under 23 USC 129(c) which authorizes federal participation in toll roads, bridges, tunnels, and ferries. FHWA has asked that Caltrans assure the ferry boat data is current for MAP-21.The Mineta Transportation Institute was initially contacted by Caltrans to conduct this census in 2012 and a report was delivered later that year. Now the census has been completed with updates through November 2018. The research team collected information from 25 water transportation operators throughout California and produced 42 accompanying maps that depict routes and terminals where the operators provide service. Tabular information for each operator catalogs their number of vessels, passenger counts, fares, seating capacity, route lengths and other data points. Note that a number of operators, despite repeated contact via phone and email, chose not to reply.This report organizes water transportation operations into three sections based on California geography: northern California, the Sacramento Delta region; and southern California. A fourth section documents four operators who did not fall within those three geographic regions.The report concludes with a listing of recreational voyage operators (e.g. cruises, fishing trips) that the authors felt did not constitute “water transportation” for the purposes of the detailed census yet may be of interest to those applying a broader definition of water transport

    Renegotiating Boundaries on Bali Coastal Tourist Resorts

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    This paper proposes a definition and application of the territorial boundary in Bali coastal tourist resorts between private owners and public space, to overcome ongoing disputes over land ownership between privately run organisations and the state. The rationale behind this investigation is in response to significant problems in these areas arising from different interests, activities and priorities being in conflict. The investigation focuses on the territorial demarcations of beaches in which a lack of effective planning law has resulted in negative impacts on social, economic, political and environmental interests. According to recent research, the area is impacted upon by physical problems emerging not only from offshore but also on shore activities. If this problem is not properly resolved then there will be serious implications for social cohesion and environmental sustainability, adversely affecting all parties and Bali as a whole. Therefore, a review of the legal, spatial and socio-political aspects of the boundary will hopefully contribute to finding a solution to sustain the areas as the most popular tourist attractions in Bali
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