Daily Archives March 7, 2016
Under appropriate conditions of temperature and pressure (Fig. 1), gas hydrates usually form one of two basic crystal structures (Fig. 2). Each unit cell of Structure I gas hydrate (Fig. 2A) consists of 46 water molecules that form two small dodecahedral voids and six large tetradecahedral voids. Structure I gas hydrates can hold only small gas molecules such as methane and ethane, with molecular diameters not exceeding 5.2 A. The chemical composition of a Structure I gas hydrate can be expressed as 8(Ar, CH4,H2S, CO2)46H2O or (Ar, CH4,H2S, CO2) 5.7H2O. The unit cell of Structure II gas hydrate consists of 16 small dodecahedral and 8 large hexakaidecahedral voids formed by 136 water molecules. Structure II gas hydrates may contain gases with molecular dimensions in the range of 5.9 to 6...Read More
Woodlands have been an essential resource for constructing homes, vehicles, ships, furniture, tools, and machines as well as for providing heat for households and cooking. Poor management of woodlands caused low productivity, and as timber stands became more remote, logging and transporting timber became less economical. During the 13th century in England, lime kilns devoured hundreds of ancient oaks in Wellington Forest. By the 1540s, the salt industry was forced to search far afield for the wood used in its processing furnaces. British navel power judged this shortage to be a national security threat. Authorities attempted to impose stiff fines for timber poaching and forbade bakers, brewers, and tile makers from purchasing boatloads of wood.
Severe timber shortages reached national cr...Read More
For millennia, the Mediterranean had been the center of international trade, with trade routes among Europe, Africa, and Asia. After the plague during the 15th and 16th centuries, Mediterranean networks of international trade with Europe declined. European nation-states were not powerful enough to govern beyond their transient borders, and inadequate local resources could not support population growth. This led to each state employing protective measures to stimulate domestic industrial production, self-sufficiency, and competition for resources. During the 16th and 17th centuries, these policies were formalized, extended, and consolidated, severely limiting the growth of trade.
The high costs of inland transportation and restrictive national practices inhibited trade opportunitie...Read More
TIMOTHY S. COLLETT
United States Geological Survey Denver, Colorado, United States
1. Implications for Gas Hydrates
2. Gas Hydrate Technical Review
3. Energy Resource Potential of Gas Hydrates
clathrate A class of compounds characterized by cages of molecules that encapsulate other molecules; from the Latin clathratus, meaning to encage.
dissociation A chemical process by which temperature and/or pressure changes cause a group of molecules to be separated into simpler groups.
methane A colorless flammable gas consisting of carbon and hydrogen.
methanol Methyl alcohol; a colorless, flammable liquid derived from natural gas.
permafrost Ground (soil or rock) that remains at or below 0°C for at least 2 years.
seismic reflectors An interface between two media with different elastic pr...Read More
Vectors of criteria for different technologies and sustainability results are shown in Table I. The current energy mix has been determined twice, first considering the nuclear percentage based on uranium-235 (mix 1) and second based on the breeder technology (mix 2). A separate control calculation with the analytical hierarchy process method has resulted in the same ranking tendency. Although fossil energy carriers use oil and gas in addition to coal, oil and gas have not been differentiated here, which should be done for more precise results. Also, in reality, hydro energy is the most significant
Vectors of Criteria for Different Primary Energy Carriers
Decreasing resources of fossil primary energy carriers and globally increasing mean per capita energy demand and population growth bring to view the question how and by which technologies the future energy supply can be guaranteed. Of primary concern here is the evaluation of the sustainability of the energy supply system. An energy supply system provides energy via different conversion technologies. In the present global energy supply system, 90% of the demand is still provided by fossil fuel-based primary energy carriers...Read More
Preindustrial economies in Britain and Europe were widespread in scale, dominated by agricultural
production, processing, and manufacture, with populations based primarily in rural villages. A range of processed goods were essential to farms and households, although restricted incomes reduced purchasing power. Solar energy, water, regional fuels, and the ebb and flow of the seasons dictated the energy of labor expenditure in workers’ lives.
There was little capital accumulation or technological progress during the widespread population destruction of the Black Death in medieval Britain and Europe...Read More
RICHARD D. PERIMAN
Rocky Mountain Research Station, USDA Forest Service Albuquerque, New Mexico, United States
especially common in the creation of textiles by spinning, weaving, and sewing. steel A strong hard metal that is an alloy of iron with carbon and other elements; it is used as a structural material and in manufacturing. work energy Defined by natural scientist James Joule as kg m         /s2 or a joule (J); it enabled physicists to realize that heat and mechanical energy are convertible.
Population growth and competition for resources have continuously been an impetus for the control and use of energy...Read More