TY JOUR TI THE POWER EFFICIENCY CALCULATION TECHNIQUE FOR MOBILE MACHINE-TRACTOR AGGREGATE USE KW assessment KW energy consumption costs KW functioning efficiency KW mathematical expectation KW energy indices KW optimum modes KW machine and tractor aggregate KW bio-energetic coefficient of efficiency JO Bulletin of KSAU AU Zhuravlev, S.Y. PY 2013 IS PB Krasnoyarsk State Agrarian University