Iranian Journal of

Background and Objectives: Sound of motorcycles plays an important role in noise pollution in big cities. This is due to the lack of national law or standards to control the noise of domestic and also imported motorcycles. This study tries to introduce a practical limit value in different stage of motorcycle life cycle by assessing their noise pollution.
Materials and Methods: First the motorcycles noise standards at different countries were studied and they were compared with the results from noise level of 622 motorcycles in 3 different groups. The sample volume in each group corresponds to the amount of their annual production rate. Then using statistical tests, a limit was determined in which 90% of the domestic motorcycles can be covered. The limit is proposed as the standard for domestic motorcycle noise.
Results: The limit for motorcycles of groups 1, 2 and 3were 84, 86 and 87 dB (A) ,respectively in the TA stage. For the COP stage (Conformity of Production), the limit increases according to certain formula. In the end, a flowchart was proposed as a standard method for measuring the sound of motorcycles in the TA and COP stages was proposed.
Conclusion: Noise level of the domestic motorcycles is at least 9 dB (A) higher than the noise limit value of European motorcycle. If European limit value is considered for producing the national motorcycle, 90% of them will get out of production cycle and this would not be practical.

Background and Objectives: The goal of the present study was to develop nanofibrous media filters containing MgO nanoparticles for future application in removing particles from gas stream.

Materials and Methods: Electrospun nanofibers were fabricated using experimental design prepared by Response Surface Methodology. Optimization of electrospinning parameters was conducted for achieving the desired filter properties including fiber diameter, porosity, and bead number. After taking SEM images, the determination of fiber diameter and number of beads were performed through Image Analysis and the calculation of porosity percent was performed by MATLAB. A filter media was produced based on the optimized conditions of electrospinning and it was certified by the HEPA filter performance test.

Results: In terms of morphological quality of fibers including fiber uniformity, absence of branching and lower numbers of beads, experiment standard No. 2 (STD 2: concentration 16 wt%, voltage 10 kV, and distance 15 cm) had the best combination. Maximum fiber diameter was also observed in STD 2. Among the electrospinning, the highest correlation coefficient was observed between solution concentration and response variables and the relationship between concentration and both fiber diameter and porosity percent was statistically significant (p <0.05 and p <0.01, respectively). A weak positive correlation was found between fiber diameter and porosity percent (r=0.29, p>0.05) and a weak negative relationship was seen between fiber diameter and bead number (r=-0.2, p>0.05).

Conclusion: Solution concentration was found as the most affecting factor on the filter properties, so that the higher concentration leaded to the lower bead number and greater fiber diameter. Increase in fiber diameter resulted in larger pore size and higher porosity. Quadratic models were known for understudy variables. Efficiency of the optimized filter was comparable with the HEPA filter and it had the lower pressure drop.