영·한 번역 2급 2교시-과학기술
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To stay competitive the industry needs to reduce to maintenance and fuel cycle costs, while enhancing safety features. Extended burnup is one of the methods applied to meet these objectives. There are a number of issues that need resolution to be able to successfully implement extended burnup. While the nuclear design of fuel can apparently be extended well beyond our current burnup limits, albeit at some economic cost, the physical performance of materials and components can have a finite end as burnup increases and no amount of analytical work will extend their life. The performance of the critical fuel components is the result of a complex interaction of a large number of variables that challenge the evaluation of the mechanisms in progress and the prediction of their behavior at extended and more severe conditions. The technologies involved include just about every aspect of materials science imaginable: properties of materials, metallurgy, structure mechanics, coolant chemistry, physical chemistry, and their basic mechanisms just to mention a few examples. In addition, exposure to radiation changes all of the physical properties and processes: the properties of the structural materials and of the coolant change. Transformations in structure and composition occur in all the materials (true alchemy!), and these processes occur in a non-homogeneous and non-equilibrium manner throughout the core.
The heat sensitivity of a pavement surface determines the bonding characteristics between the surface and most hot-applied marking materials. At temperatures greater than 160°F, asphalt behaves as a viscous liquid, which allows for thermal bonding with many hot-applied pavement marking materials. For example, thermoplastic materials bond to asphalt surfaces by melting and fusing with the asphalt. Thermal bonding provides for a tight bond between the surface and the marking. Concrete pavements do not react to hot-applied pavement markings in this way, and as such thermal bonding does not occur. In these cases, other bonding mechanisms are relied upon, which are often inferior to thermal bonding. It is for this reason that some hot-applied marking materials, such as thermoplastic, are not recommended for use on concrete surfaces. The surface porosity of a pavement surface determines the mechanical bonding characteristics for pavement markings with the surface. Mechanical bonding occurs when the pavement marking material seeps into the pores of the pavement surface and creates a tight mechanical bond upon drying. Thermoplastics and other hot-applied pavement markings adhere to concrete through mechanical bonding. Traffic volumes greatly influence the performance of a pavement marking regardless of the pavement surface. The service lives of nearly all pavement marking materials are decreased when exposed to higher traffic volumes. However, some materials are clearly more resistant to traffic than others.
The potential effects of climate variability and change on ecosystems and human activities will not be determined solely by their sensitivity and adaptability, but also by multiple, cumulative interactions among physical, ecological, economic, and social conditions. For example, some crops and plants that might otherwise experience reductions in productivity as a result of changes in climate alone could actually experience increased growth and productivity as a result of increases in atmospheric CO2 concentrations and nutrients (from deposition and runoff). Other species and ecosystems, which could adjust to climate change alone, might be endangered when land use and other factors interfere with adaptive mechanisms such as migration. Interacting factors must be identified and understood to develop accurate projections of effects. The CO2 “fertilization effect” (increased plant growth due to higher atmospheric CO2 concentrations), nitrogen deposition, disturbance (e.g., fire, pest infestations), land-cover fragmentation, air pollution, and other factors affect the functioning (e.g., water use efficiency, biomass allocation) and composition of natural and managed ecosystems over long periods of time. Similarly, estuarine and coastal ecosystems face multiple-stressor problems associated with point source and non-point source pollution, increased sedimentation resulting from upstream land-use practices, invasive species and sea-level rise.