Thee attention it takes people to focus at work drains them of psychological, social and material reserves, says Dr. Cunningham, leading to stress and lower productivity.

Chen's entire oeuvre is defined by his references and reserves - a mixed grab bag of material and inspiration that is open for all to see, coalescing in various forms that gather in various series.

But in the economic evaluation to the gas reserves, we are always difficult to carry on the accurate valuation because of lacking the related material.