Buffer thermal energy storage for an air Brayton solar engine

The application of latent-heat buffer thermal energy storage to a point-focusing solar receiver equipped with an air Brayton engine was studied. To demonstrate the effect of buffer thermal energy storage on engine operation, a computer program was written which models the recuperator, receiver, and thermal storage device as finite-element thermal masses. Actual operating or predicted performance data are used for all components, including the rotating equipment. Based on insolation input and a specified control scheme, the program predicts the Brayton engine operation, including flows, temperatures, and pressures for the various components, along with the engine output power. An economic parametric study indicates that the economic viability of buffer thermal energy storage is largely a function of the achievable engine life

Natural Gauge Hierarchy in SO(10)

It is shown that a natural gauge hierarchy and doublet-triplet splitting can be achieved in SO(10) using the Dimopoulos-Wilczek mechanism. Artificial cancellations (fine-tuning) and arbitrary forms of the superpotential are avoided, the superpotential being the most general compatible with a symmetry. It is shown by example that the Dimopoulos-Wilczek mechanism can be protected against the effects of higher-dimension operators possibly induced by Planck-scale physics. Natural implementation of the mechanism leads to an automatic Peccei-Quinn symmetry. The same local symmetries that would protect the gauge hierarchy against Planck-scale effects tend to protect the axion also. It is shown how realistic quark and lepton masses might arise in this framework. It is also argued that ``weak suppression'' of proton decay can be implemented more economically than can ``strong suppression'', offering some grounds to hope (in the context of SO(10)) that proton decay could be seen at Superkamiokande.Comment: 26 pages in plain LaTeX, 5 figures available on request, BA-94-0

Employee Health Benefits: Corporate Strategies for Cost Containment

With health care costs increasing and a major portion of employee benefits attributableto health care, employers have turned their attention to a range of strategies for controllingcosts. A typology of the employer role in employee health care is presentedwhich suggests that cost containment strategies may bring increasing influence by theemployer in the health care decisions of employees. Four roles for employers havebeen identified: (1) the Enabler, providing traditional health benefits, with increasinguse of deductibles and copayments; (2) the Advocate, providing benefit and alternativedelivery options (e.g., HMOs) with incentives for less costly choices; (3) the Mediator,providing programs which intervene in health care utilization decisions (e.g., secondsurgical opinions); and (4) the Provider, providing direct services at the workplace(e.g., screening and health promotion programs). Implications for employers, employees,and the health care system are raised

Producing cellulose-reinforced biocomposite films from biomass using ionic liquids

Biomass and its lignocellulosic components are complex polymeric materials underutilized for their impressive mechanical properties. As the structural support material of plants, lignocellulosic biomass derives its strength and stiffness from the microscopic morphology of its cells, whose walls are composed of precisely aligned cellulose microfibrils known to have exceptional tensile properties. These microfibrils are reinforced by agglomerations of lignin and hemicellulose, making biomass a natural composite. However, as fluid transport is necessary even in the dead structural support tissue of plants, much of the volume of lignocellulosic biomass is void. Physical densification has been shown to improve its mechanical performance. Therefore, chemical densification, by way of selectively dissolving the non-cellulosic fraction of biomass in ionic liquid to form a cellulose-microfibril-reinforced biopolymer composite, should also yield improved mechanical properties. Unlike physical densification, this process is intrinsically scalable, as it is not limited by the size of feedstock particles. Ionic liquids are salts with sufficiently low melting points to be conveniently used in liquid form. They are stable, non-flammable, and offer immeasurably low vapor pressures, meaning they are safer to transport, work with, and dispose of than traditional polymer solvents. They may also be reused after mixing with lighter solvents like water by vacuum distillation, making them a relatively sustainable choice for polymer dissolution. In that biomass is renewable, it may also be sustainable—though far more so when it derives from forestry or agricultural waste, which comprise the majority of available lignocellulosic biomass (the largest stream of non-edible biomass globally). The two primary challenges associated with this manufacturing process are the same: dissolving highly polymerized lignin from whole biomass and regenerating lignin to form a solid film during ionic liquid removal. Essentially, depolymerizing and depolymerizing lignin. To address the first challenge, ionic liquid chemistry and dissolution conditions were optimized. To address the second, two methods were tested: radical polymerization of the dissolved non-cellulosic portion of biomass; and partial dissolution of cellulose to form a solid matrix for other biopolymers during regeneration. Related parameters such as curing, drying, and regeneration conditions were also optimized. Dynamic mechanical performance and microstructure of thin films produced using this method (which preserves the native cellulose-I structure) were compared to those of biomass films containing fully dissolved and regenerated cellulose (cellulose-II), and to those of films made from equivalent mixtures of extracted lignocellulosic components. The effect of biomass composition on this performance, modulated directly in component mixtures and by wood species in biomass films, was also investigated. The produced composites may offer a sustainable alternative to traditional glass fiber-reinforced polymers for high-volume structural applications

Simulating Impacts of Extreme Weather Events on Urban Transport Infrastructure in the UK

Urban areas face many risks from future climate change and their infrastructure will be placed under more pressure due to changes in climate extremes. Using the Tyndall Centre Urban Integrated Assessment Framework, this paper describes a methodology used to assess the impacts of future climate extremes on transport infrastructure in London. Utilising high-resolution projections for future climate in the UK, alongside stochastic weather generators for downscaling, urban temperature and flooding models are used to provide information on the likelihood of future extremes. These are then coupled with spatial network models of urban transport infrastructure and, using thresholds to define the point at which systems cease to function normally, disruption to the networks can be simulated. Results are shown for both extreme heat and urban surface water flooding events and the impacts on the travelling population, in terms of both disruption time and monetary cost

A Simple Grand Unified Relation between Neutrino Mixing and Quark Mixing

It is proposed that all flavor mixing is caused by the mixing of the three quark and lepton families with vectorlike fermions in 5 + 5-bar multiplets of SU(5). This simple assumption implies that both V_{CKM} and U_{MNS} are generated by a single matrix. The entire 3-by-3 complex mass matrix of the neutrinos M_{nu} is then found to have a simple expression in terms of two complex parameters and an overall scale. Thus, all the presently unknown neutrino parameters are predicted. The best fits are for theta_{atm} less than or approximately 40 degrees. The leptonic Dirac CP phase is found to be somewhat greater than pi radians.Comment: 10 pages, 4 figures, one table. Typos correcte