货物集装箱扫描技术的发展

恐怖分子利用货物集装箱走私核武器或用于放射性频散装置(RDD)的放射性材料,美国和其他国家目前都在面临这一严重威胁.     

The changing status of water as a natural resource

This paper considers the way freshwater resources are perceived in an era of climate change. It is suggested that in many parts of the world water is moving from being a renewable resource (or continuous natural resource) to a potentially renewable resource (PRR). In some areas water is moving from being a PRR to a nonrenewable resource. Selected water problems from three continents are investigated in the context of this theoretical construct. Recent experience in the United Kingdom is then also investigated as a case study of these changes before brief conclusions are drawn.     

Economic aspects of natural resource exploitation

Low entropy accumulations of matter and energy are more economic for humans to exploit as natural resources. This accumulation of a resource takes place over time and the most concentrated resources, such as fossil fuels, are created over geological ages. As the most concentrated resources become depleted it may be possible for technology to enable the exploitation of less concentrated resources, such as low-grade metal ores or thinly populated fishing grounds. Analysis of the timescales necessary to create different types of natural resource reveals three distinct groups. Further consideration of economic characteristics of resources, including ownership and access, and rate of consumption relative to rate of supply confirms the grouping of resources into the three distinct groups. Rate of change of entropy as a resource is exploited is an indicator of its impact on the environment. Consideration of this again suggests three distinct groups of resources, and this paper identifies them as: continuous natural resources (CNR), such as solar power and wind power; potentially renewable resources (PRR), such as fish and forests; and non-renewable resources (NRR), such as fossil fuels and metals.