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I attach three papers that have been published in some special journals and may be of interest to scientists working on FBP. I suppose that the topics of these papers may be classified from the mathematical point of view as Free Boundary Problems.

1. The first paper presents a new mathematical model of groundwater evaporation in soils that has a simple formulation and contents only one moving unknown phase transition boundary.

2. The second one is about gas hydrates dissociation and formation in gas fields (a short version of the paper was published in Annals of the New York Academy of Sciences, 2000, V. 912, p.428-436.

   Gas hydrates are crystalline ice-like solids that form when water and sufficient quantities of certain gases are combined under the right conditions of temperature and pressure. Under these conditions, the amount of gas stored in a given volume of hydrate is 170 times higher than when the gas is at standard conditions. This fact contributes to its potential as an economically recoverable energy source. Substantial amounts of hydrates have been found in the Earth's sediments beneath the permafrost and in ocean bottom sediments along the continental margins. Therefore the problems associated with the production of natural gas from these hydrate zones have become of greater interest to the hydrocarbon industry.

   Gas hydrate dissociation problems in natural reservoirs can be formulated as a generalization of the classical Stefan problem. We have found that there exist a few different regimes of gas hydrates decomposition with the formation of two or more unknown moving phase transition boundaries and formation of extended phase transition zone ("mushy region"). These problems are close to the ground freezing problems as gas hydrates are motionless in a natural formation.

3. The third paper deals with the vaporization and condensation problems in geothermal reservoirs. In this case we have obtained water superheating ahead of a vaporization front that leads (as supercooling for the crystallization problem) to a two-phase zone ("mushy region") formation. Water-vapour phase transition problem in geothermal reservoirs is a more complex problem and more rich as both phases can move through a permeable porous rock.

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