• This counterintuitive finding reflects two key characteristics about energy markets: the worldwide increase in renewable energy sources whose output is intermittent and variable; and greater market liberalization, which has made the spot pricing of electricity more volatile. The intermittency of renewable energy sources requires backup generation, typically from generators using fossil fuels....

Different quality, reserves and production force countries to import fossil fuels to advance their economic development. It is exergy of fossil fuels that is essentially important to economy. Thus, it forms an international exergy flow network embodied in the global fossil energy trade. Based on complex network theory, we built a global fossil energy exergy flow network with countries as nodes,...

The fossil record provides the primary source of data for calibrating the origin of clades. Although minimum ages of clades are given by the oldest preserved fossil, these underestimate the true age, which must be bracketed by probabilistic methods based on multiple fossil occurrences. Although most of these methods assume uniform preservation rates, this assumption is unsupported over geologic...

—Approximately one-fifth (ten species) of the plant megafossils in the Chinle Formation in Petrified Forest National Park, Arizona are the remains of ferns or fern-like leaves. Four of the species are assigned to living families, two are assigned to extinct families and the others are unassigned. The nearest living relatives and morphological features of these plants indicates that they lived u...

Article history: Wereport the results of a sta Received 10 December 2007 Received in revised form 25 February 2008 Accepted 3 March 2008 Available online 13 March 2008 Editor: H. Elderfield

English)