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Abstract. On-road vehicle tests of three diesel trucks were conducted by a portable emission measurement system (PEMS) in Chengdu, China. SEMTECH-ECOSTAR provided by Sensors, Inc and MI2, an emissions measuring instrument powered by the Pegasor Particulate Sensor (PPS) were employed to detect gaseous and particle emissions during the tests. The impacts of speed and acceleration on emissions were analyzed. The average NOx emission factors of the heavy duty diesel truck (HDDT), medium-duty diesel truck (MDDT), light duty diesel truck (LDDT) were 7.29, 5.29 and 5.53 g/km, all of which were in excess of their emission limits. The particle emission factors were 0.60, 0.30 and 0.14 g/km, generally higher than the results for similar reported in the previous studies. Both gaseous and particle emission exhibit significant correlations with the change in vehicle speed, acceleration and power demand. The highest emission for each vehicle were generally found in high-VSP. High engine power caused by aggressive driving or heavy load is the main factor of high emissions for the vehicles in real-world situation.

It is known that every triangle-free plane graph is 3-colorable. However, such a triangle-free plane graph may not be 3-choosable. In this paper, we prove that a triangle-free plane graph is 3-choosable if no 4-cycle in it is adjacent to a 4-or a 5-cycle. This improves some known results in this direction.