Optimization of gearbox housing shape for agricultural UTV using structural-acoustic coupled analysis.

In this study, gearbox radiated noise was successfully reduced through housing shape optimization. First, dynamic and structural-acoustic coupled analysis models of an agricultural UTV gearbox were developed. Then, the test equipment was configured to match that of the simulation model, and a test was conducted. The analysis and test results showed errors within 0.1 dB for vibration and 0.2 dB(A) for noise, indicating that the models were reliable. The housing design was then optimized using topology optimization based on the developed structural-acoustic coupling analysis model. The sound pressure level around the housing was used as an objective function for topology optimization. The optimal distribution of materials for the housing was also derived to reduce the radiated noise. Lastly, the housing rib was designed based on the optimization result, and an improvement in the radiated noise by approximately 2.43 dB(A) was confirmed in the operation area.

Effect of sound insulation on noise reduction in an agricultural tractor cab.

Tractor cab interior noise is a risk factor that degrades operators' work performance and threatens their health; therefore, the noise must be reduced to ensure farmworkers' safety and efficiency. Cab interior noise can be classified as structure-borne noise and air-borne noise. Structure-borne noise has been extensively studied. However, although air-borne noise greatly contributes to cab interior noise, detailed frequency-domain analyses have not been performed. In this study, the components of cab interior noise were identified in the frequency domain through an order analysis, which helped improve the sound insulation of the cab and reduce the effects of air-borne noise. A test was performed while driving a tractor on a chassis dynamometer in a semi-anechoic chamber for reproducible measurement and evaluation. The A-weighted sound pressure was transformed by a fast Fourier transform algorithm, and its order was tracked by the engine speed signal. In addition, a direct path was identified by acoustic images using a sound camera. The contributions of major noise sources were identified through an order analysis. We proved that air-borne noise significantly contributes to the interior noise of tractor cabs and that improvement of the cab sound insulation is an effective noise-reduction technique.

New predictive equations for spirometric reference values and comparison with Morris equation in a Korean population.

BACKGROUND AND OBJECTIVE: The clinical importance of the differences between actual and predicted spirometric indices in non-Western populations is poorly defined. This study evaluated the differences between the spirometric values derived from Morris equation, traditionally used in South Korea, and the actual values, in the classification and detection of patients with respiratory diseases, and developed new predictive equations for the calculation of reference spirometric values for healthy Koreans. METHODS: Data derived from a subset of the population who completed the initial baseline survey of the Korean Health and Genome Study were used to develop new predictive equations for spirometric reference values, using multiple linear regression. The effects of the new equations relative to those of Morris on the detection and classification of patients with respiratory diseases were then evaluated. RESULTS: In total, 9999 people completed the baseline survey; a subgroup of 1314 met the study inclusion criteria and were used to develop the new predictive equations. Morris equation are 53.8% less accurate in detecting people with restrictive disorders and 15.8% less accurate in estimating the severity of COPD than the newly derived equations, although the differences between values derived from the traditional equations and values from the new equations were as small as 3.3-7.6%. CONCLUSIONS: The use of spirometric reference values that underestimate the actual parameters, despite the small differences, may have a significant influence on the detection of patients with restrictive disorders and the staging of COPD.

Sero-epidemiology of measles and mumps in Korea: impact of the catch-up campaign on measles immunity.

A catch-up campaign targeting children aged 8-16 years using measles-rubella (MR) vaccine was conducted during 2001 in Korea. To evaluate the impact of the campaign and assess mumps immunity, human IgG antibodies were detected using ELISA for measles (5826 samples) and mumps (5890 samples) in a national sample of opportunistically collected sera from a population aged 0-34 years. The measles immunity increased by 5-10% following the catch-up campaign in the targeted age group. Infants lost maternal antibodies rapidly and about 90% of infants were susceptible to measles and mumps at 6-8 months of life. The sero-prevalence of mumps antibody increased slowly with age and stabilized at a lower level when compared with that of measles. Despite an immediate reduction in susceptibility among the targeted age group of the catch-up campaign, continuous efforts to increase immunization coverage are needed to interrupt indigenous measles transmission. Furthermore, our results suggest continuous mumps outbreaks could occur because of the accumulation of susceptible individuals.