Thermal conductivity is a thermodynamic parameter playing an important role in the heat transfer process in geothermic and numerous engineering fields. In order to analyze the factors influencing the thermal conductivity of sandstone, the data of thermal conductivity obtained from the literatures in China and abroad were summarized. The influences of porosity, moisture and fluidic content, pressure and temperature on the thermal conductivity were analyzed and discussed. The survey results show that the thermal conductivity of sandstones mainly depends on its mineralogical composition, microstructure, porosity, saturation, pressure and temperature. It increases with the degree of fluid saturation and pressure, while decreases with the increase of porosity and temperature. The result of analysis shows that when the degree of saturation is higher than 15 %, the thermal conductivity curve is a linear function of the degree of saturation. ARTICLE INFO

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Push-to-Talk over Cellular (PoC) system is ideal for group communication in many cooperative work environments because of its wider coverage and more flexibility than traditional trunk communication systems. The long sessionsetup-delay is an important problem that must be solved before the commercial application of PoC system. Many research works have been done to solve it in some mobile networks, such as CDMA2000, WCDMA, etc. This paper elaborates one designed PoC system which is based on TD-SCDMA mobile network. In the beginning, we introduce some research activities related to establishing PoC system of short session-setup-delay. Then the design of hardware and software of the proposed PoC system is described. Some solutions for the key techniques of this system are also illustrated. Testing results show the designed system can achieve short sessionsetup-delay satisfying the commercial application.

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