1,564 research outputs found

    Revisiting the Tradespace Exploration Paradigm: Structuring the Exploration Process

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    A number of case applications of tradespace exploration have further extended the types of analyses and knowledge insights that can be gained about tradeoffs between design choices and perceived utility and cost of alternatives. These extensions include application beyond its heritage aerospace domain to the transportation domain, comparing distinct concepts on a common tradespace, considering the impact of changing needs and contexts over time, evaluation of alternatives in a “light effort” manner. In parallel with these case applications, a formalization of the tradespace exploration process has emerged, using a question-driven approach to ensure the knowledge generated is practical and useful to decision makers. These questions are introduced and applied to three example space systems in order to illustrate insights gained in answering the questions. The insights include identifying “good” designs, the strengths and weakness of selected alternatives across a tradespace, limiting constraints and requirements that could allow for less expensive solutions. Additionally, advanced insights include understanding the sensitivities of designs to changes in contexts and needs, and consideration of the differential impact of uncertainty across a set of alternatives with potential opportunities for risk mitigation.Massachusetts Institute of Technology. Engineering Systems Division (Systems Engineering Advancement Research Initiative (SEAri)

    Role for Interactive Tradespace Exploration in Multi-Stakeholder Negotiations

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    The significant time, effort, and resource expenditures needed to design and develop aerospace systems motivate on-going research into developing methods for generating, evaluating, and selecting candidate system solutions that can deliver more benefit for a given cost. Compounding the problem is the multiplicity of perspectives of the many stakeholders for such systems, altering the meaning of “benefit” and “cost” depending on the stakeholder considered. Tradespace exploration techniques have been used in the past to generate large datasets in order to gain insights into design-value, cost-benefit tradeoffs for complex aerospace systems. Using interactive tradespace exploration to support multi-stakeholder negotiations can reveal these tradeoffs not only for individuals, but also across a group. A method is introduced and applied to two aerospace cases in order to explore the potential for interactive tradespace exploration to support stakeholder negotiations. Preliminary results indicate the method to be a rapid and beneficial technique, which generated compromise alternatives, guided the elicitation of previously unarticulated information, and resulted in increased confidence and solution buy-in of participating stakeholders.Massachusetts Institute of Technology. Systems Engineering Advancement Research Initiativ

    Multi-Epoch Analysis of a Satellite Constellation to Identify Value Robust Deployment across Uncertain Futures

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    The value of a system depends heavily on the future contexts it will encounter. For complex space systems with multi-year design and deployment phases, it is useful to design a system so that it delivers value to stakeholders over a wide range of future contexts. Epoch-Era Analysis, a computational scenario planning approach, decomposes the lifecycle of a system into sequential epochs that each have fixed contexts and value expectations. This paper applies Multi-Epoch Analysis (a subset of Epoch-Era Analysis) along with Multi-Attribute Tradespace Exploration (MATE) to the design of a satellite constellation, with the aim of maximizing value across a range of end-user subscription and geographic distribution contexts. The system level tradespace is assembled using a bottom-up iterative approach based on expert knowledge, and accounts for performance attributes metrics such as revisit times, data latencies, observation times, and data downlink volumes. Competing designs consisting of alternative orbital, ground station location, and deployment configurations are evaluated in terms of their fuzzy Normalized Pareto Trace (fNPT) across epochs. The resulting staged deployment strategy delivers robust value based on stakeholder preference across a wide range of future contexts. Nomenclature DZ = deployment design variable index Z fNPT = fuzzy normalized pareto trace GY = ground station design variable index Y K = fuzziness factor MAU = multi-attribute utility NPT = normalized pareto trace OX = orbit design variable index X I

    Techniques in improving project sustainability

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    Techniques in improving project sustainabilit

    The care and education of pauper children in England and Wales, 1834 to 1896

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    This study reviews the measures taken by public authorities in England and Wales between 1834 and 1896 to provide for the care and education of children chargeable to the poor rate. The various types of institution in which these children were maintained are described. The development of what amounted to a system of state schools for a special class of child,predating the board schools of the 1870s by a generation, is noted; particular attention is paid to the district schools, some of which were amongst the most remarkable working-class schools of the nineteenth century. Problems surrounding the recruitment and training of teachers for pauper schools are investigated and a summary is given of the orthodox theory and practice of education applied to the nurture of the pauper children. The administrative hierarchy, including the inspectorate, is outlined and the clash between the educational and poor la authorities is described. Notice is also taken of the significant development of unorthodox methods which led to the pauper children being removed from institutions and settled into small homes or even individual families. Finally the means adopted for easing the pauper children into the working community are described together with the development of what is now called 'after care'. The period initiated by the introduction of the new poor law in 1834 was, for the children, brought to an end in 1896 when a Departmental Committee condemned the institutional methods typical of the previous sixty years, and pressed upon the authorities the hitherto unorthodox non-institutional methods which have since become the standard means of providing for the deprived child

    The modelling and measurement of nuclear reaction cross-sections & the production of a technetium fission yield tracer

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    The 20th^{th} century saw the dawn of the nuclear age, in which humanity harnessed the strong nuclear force through the nuclear processes of fission and fusion. Nuclear science expanded our understanding of matter beyond chemical elements, to include over 7,000 predicted nuclei, each with discrete characteristics born out of their nuclear structure. An understanding of nuclear reactions and decay of nuclei enabled energy production with densities orders of magnitude greater than traditional means, and the diagnosis and treatment of a range of diseases. These advancements also came with baggage in the form of security and environmental challenges. The characterisation and detection of radionuclides is of huge importance in nuclear science, whether that be optimising the operation of nuclear reactors based on the distribution of fuel products, the detection of clandestine nuclear activity by rogue states through the detection of products produced in nuclear weapons testing, and the mitigation of environmental damage by accurately being able to quantify the transport of radionuclides through matter and the biosphere. All isotopes of a given element act chemically identically due to their identical electron configuration, however, they each possess unique physical fingerprints in the form of decay channels, reaction probabilities, and reaction mechanisms. The combination of these factors opens up a realm of possibilities, whereby the chemical transport of different isotopes of the same element is identical, while the presence of different isotopes can be determined by their unique nuclear characteristics, two facts which are leveraged with radiotracers. The field of radiotracers is ubiquitous in medicine, energy, and nuclear security, with the production of high-purity radioactive isotopes with specific physical and chemical characteristics for a range of applications in an evolving field. The development of such a tracer involves several stages, centering around the optimisation of nuclear reactions to enable the production of exotic elements and isotopes often not present in nature, which through optimised particle accelerator production combined with a series of refined chemical separation steps can produce high isotopic purities. This thesis focuses on developing a radio-tracer of 97^{97}Tc for the analysis of long-lived fission product 99^{99}Tc. The workflow can act as an effective template for future tracer development, with clear steps from concept to a standardised tracer suitable for commercial deployment. With 99^{99}Tc being a high-yield fission product produced 6.1% of the time in thermal neutron-induced fission of 235^{235}U [1], a commercially viable mass tracer for technetium-99 is highly sought after in the nuclear industry, with applications in nuclear security, decommissioning, environmental monitoring and optimising reactor power cycles. As a mass spectrometry tracer of 99^{99}Tc, 97^{97}Tc was determined as the only suitable candidate isotope, produced indirectly through the decay of a 97^{97}Ru generator. Six reactions were then compared using natural abundance targets: nat^{nat}Mo(3^{3}He,xn)97^{97}Ru, nat^{nat}Mo(α,xn)97^{97}Ru, nat^{nat}Ru(p, X)97^{97}Ru, nat^{nat}Ru(d, X)97^{97}Ru, nat^{nat}Ru(3^{3}He,X)97^{97}Ru, and nat^{nat}Ru(α,X)97^{97}Ru. A computational tool for the running of nuclear reaction modelling and isotope inventory calculations called ”The University of Birmingham Tool for Isotope Production (UoB-TIP)” was developed during this project. This software enabled a range of nuclear reactions to be modelled using TALYS and TASMAN nuclear reaction codes and FISPACT-II transmutation code. This enabled the rapid comparison of accelerator-driven production routes, while also executing the parsing and visualisation of data, enabling determination of the optimum target-beam combination, particle energy, and the time to chemically separate to maximise quantity and purity. Quantitative results from this software package, along with coordination with the National Physical Laboratory on the potential chemical purification, nat^{nat}Mo(α, xn)97^{97}Ru was determined to be the most promising reaction. This is due to the large cross-section of 97^{97}Ru production, high threshold energy of contaminant isotope 99^{99}Mo, and a novel separation scheme developed during this project which utilised the recently developed TK202 extraction chromatography resin. A high-precision nuclear reaction cross-section method was developed for charged particle spectroscopy at the University of Birmingham MC40_{40} cyclotron, including experimental set-up and semi-automated analysis software. This method was used to improve accuracy in nuclear reaction cross-sections for Mo-α, with the method and experimental results in this thesis. Following this, a novel chemical separation method was developed at the National Physical Laboratory using TK202 resin. The optimum operating conditions were found to be 5M NaOH for a high retention of Tc. This enables easy separation of the Tc produced in the reaction from the 97^{97}Ru generator with a successive step extracting the 97^{97}Tc, produced through the decay of the tracer with a half-life of 2.83(32) d, from any stable Ru and Mo in the remaining target

    Travelling waves in a mixture of gases with bimolecular reversible reactions

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    Starting from the kinetic approach for a mixture of reacting gases whose particles interact through elastic scattering and a bimolecular reversible chemical reaction, the equations that govern the dynamics of the system are obtained by means of the relevant Boltzmann-like equation. Conservation laws are considered. Fluid dynamic approximations are used at the Euler level to obtain a close set of PDEs for six unknown macroscopic fields. The dispersion relation of the mixture of reacting gases is explicitly derived in the homogeneous equilibrium state. A set of ODE that governs the propagation of a plane travelling wave is obtained using the Galilei invariance. After numerical integration some solutions, including the well-known Maxwellian and the hard spheres cases, are found for various meaningful interaction laws. The main macroscopic observables for the gas mixture such as the drift velocity, temperature, total density, pressure and its chemical composition are shown.Comment: 13 pages, 2 figures, accepted on Physica

    Trends in sexually transmitted infections in general practice 1990-2000: population based study using data from the UK general practice research database

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    Objective: To describe the contribution of primary care to the diagnosis and management of sexually transmitted infections in the United Kingdom, 1990-2000, in the context of increasing incidence of infections in genitourinary medicine clinics. Design: Population based study. Setting: UK primary care. Participants: Patients registered in the UK general practice research database. Main outcome measures: Incidence of diagnosed sexually transmitted infections in primary care and estimation of the proportion of major such infections diagnosed in primary care. Results: An estimated 23.0% of chlamydia cases in women but only 5.3% in men were diagnosed and treated in primary care during 1998-2000, along with 49.2% cases of non-specific urethritis and urethral discharge in men and 5.7% cases of gonorrhoea in women and 2.9% in men. Rates of diagnosis in primary care rose substantially in the late 1990s. Conclusions: A substantial and increasing number of sexually transmitted infections are diagnosed and treated in primary care in the United Kingdom, with sex ratios differing from those in genitourinary medicine clinics. Large numbers of men are treated in primary care for presumptive sexually transmitted infections

    Estuarine Forecasts at Daily Weather to Subseasonal Time Scales

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    Most present forecast systems for estuaries predict conditions for only a few days into the future. However, there are many reasons to expect that skillful estuarine forecasts are possible for longer time periods, including increasingly skillful extended atmospheric forecasts, the potential for lasting impacts of atmospheric forcing on estuarine conditions, and the predictability of tidal cycles. In this study, we test whether skillful estuarine forecasts are possible for up to 35 days into the future by combining an estuarine model of Chesapeake Bay with 35-day atmospheric forecasts from an operational weather model. When compared with both a hindcast simulation from the same estuarine model and with observations, the estuarine forecasts for surface water temperature are skillful up to about 2 weeks into the future, and the forecasts for bottom temperature, surface and bottom salinity, and density stratification are skillful for all or the majority of the forecast period. Bottom oxygen forecasts are skillful when compared to the model hindcast, but not when compared with observations. We also find that skill for all variables in the estuary can be improved by taking the mean of multiple estuarine forecasts driven by an ensemble of atmospheric forecasts. Finally, we examine the forecasts in detail using two case studies of extreme events, and we discuss opportunities for improving the forecast skill
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