Estimate the maximum possible value of the thermal conductivity coefficient of a cylinder with a diameter d = 3 mm made of crystalline artificial sapphire at a temperature of 30 K. The Debye temperature of sapphire is Q = 100 K, the speed of sound is s = 104 m/s, and its heat capacity at T Q is determined by the expression CV = 0 ,1T3 J/(m3•K).

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