Permafrost by permafrost. Of this area slightly more than half is underlain by continuous permafrost, around 20 percent by discontinuous permafrost, and a little less than 30 percent by sporadic permafrost. Most of this area is found in Siberia, northern Canada, Alaska and Greenland. Beneath the active layer annual temperature swings of permafrost become smaller with depth. The deepest depth of permafrost occurs where geothermal heat maintains a temperature above freezing. Above that bottom limit there may be permafrost, whose temperature doesn't change annually—"isothermal permafrost". Permafrost typically forms in any climate where the mean annual air temperature is less than the
Crystallographic defects in diamond inclusions. Gray color in some diamonds from the Argyle mine in Australia is often associated with those hydrogen defects, but again, this assignment is yet unproven. When diamonds are grown by the high-pressure high-temperature technique, nickel, cobalt or some other metals are usually added into the growth medium to facilitate catalytically the conversion of graphite into diamond. As a result, metallic inclusions are formed. Besides, isolated nickel and cobalt atoms incorporate into diamond lattice, as demonstrated through characteristic hyperfine structure in electron paramagnetic resonance, optical absorption and photoluminescence spectra, and the concentration of isolated nickel can reach 0.01%. This fact