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Coalbed methane embedded in coal seams, is an unconventional energy resource as well as a hazardous gas existing in mining industries, which attracts lots of global attention. As the largest coal producer, the mining industry in China had to deal with many hazards induced by methane for decades. To solve this issue, underground methane extraction is commonly used in underground coal mines. However, underground methane extraction is hampered by low production rate and low efficiency because of slow gas emission from coal primarily controlled by gas desorption and permeability. It is well known that temperature has a great impact on gas sorption. The higher the temperature the larger the desorption rate. As the depth of coal mines increases beyond 1000m coal mines suffer elevated air temperatures caused by the natural geothermal gradient. The elevated temperature in such mines provides a potential economical way for geothermal energy extraction and utilization in deep coal mines which can largely cut the expenses of installation and operation maintenance. Therefore, a novel method is proposed to enhance underground methane extraction by deep heat stimulation. This paper mainly presents an assessment of previous and ongoing research in the related field and provides a first feasibility analysis of this method applied in the underground environment. The technique proposed in this early appraisal is deemed significant for coalbed methane drainage enhancing the productivity of deep coal mines by geothermal technology and can also be extended for many applications in relevant areas such as shale gas, and tight oil.

String theory is constructed on group manifold which is locally neither a Minkovski nor a Euclidean space. It is shown that Lorentz algebra is satisfied and ghost states can all be eliminated. The string theory constructed is just like a string theory in four dimensions.

We have completely integrated out the field equations to obtain all spherically symmetric electric monopole solutions in the five dimensional Kaluza-Klein theory. A specific solution is given and its relevance to the classical theory of electron is discussed.

The rules of truncation for getting a gauge invariant action from a gauge-fixed action are put forward and completed. It is shown that the presently well-known gauge invariant action (ψ|QB|ψ) can also be obtained by means of truncation. The confusion of considering this action as a gauge-fixd action is clarified.