Iranian Journal of

Background and Objective: Noise pollution is one of the serious environmental issue. Sound control technologies based on sound absorption and sound insulation are considered as the two widely used methods. Therefore, the aim of this study was to modify silica aerogel nanocomposites to improve its acoustic properties.
Materials and Methods:  This applied experimental research involved in examining eight various types of nanocomposites to evaluate their performance of acoustic properties. In this study, nanocomposites were synthesized by sol-gel method. For this purpose, TEOS and ethanol were added to SiO₂ which subsequently stirred and diluted with ethanol as a precursor of silica sol. A solution of 5.5 M ammonium hydroxide is added drop-wise to the silica sol and then was stirred. The activated silica sol was quickly poured into the mold in which the samples were placed and finally placed in an oven at 150 °C for 3 hours. The acoustic properties of the samples were measured by the impedance tube and the reduction sound pressure level using a sound level meter. Each sample morphology was characterized by scanning electron microscopy.
Results: The sound absorption properties of as prepared nanocomposite relatively increased at high frequencies. The results indicated > 0.6 sound absorption coefficient by the modified nanocopmosites at higher frequencies. The sound absorption coefficient and transmission loss of D1 nanocomposite were higher at medium and low frequencies as compared to other nanocomposites. 4.6 and 9.73 dB average reduction of sound pressure level were achieved by either with or without nanocomposite enclosure, respectively, at a distance of 1 meter.   
Conclusion: The results of the current study showed that the simultaneous addition of organic and mineral materials to silica aerogels (especially with the highest amounts of nanoclay) improves its acoustic properties, especially at medium and low frequencies. Among the samples, D1 nanocomposite shows better acoustic properties at medium and low frequencies. The sound absorption coefficient of D1 nanocomposite at frequencies of 315, 400, 500, 1000, 1250, 2000 Hz were obtained as 0.27, 0.38, 0.51, 0.78, 0.83 and 0.84, respectively. The findings also indicated 9.37 dB reduction of sound pressure level using D1 nanocomposite.

Background and Objective: Scientometrics is used to identify existing study gaps, discover the future research directions, investigate fundamental trends and implement the necessary policies in a specific field of knowledge. Considering the key role of environmental factors in the health trends and the varyingburden of diseases in the country, this study was conducted with the aim of performing scientometric analysis of the role of environmental health in the prevention and control of diseases related to environmental factors in Iran.
Materials and Methods: Bibliographic information related to scientific documents indexed in the Web of Science database until September 12, 2022, was analyzed and visualized using Citespace and Biblioshiny software.
Results: A total of 1,212 documents were retrieved. These documents were published in 629 sources with the participation of 8,461 authors. The average publication year of the documents was 2010. The top three ranks of organizational affiliations were as follows: Tehran University of Medical Sciences (747 documents), Isfahan University of Medical Sciences (436 documents), and Shahid Beheshti University of Medical Sciences (393 documents). Iran's cooperation network with other countries indicates substantial joint researchbetween Iran and the main countries in this network. Over time, the co-occurrence network of keywords has evolved from outcomes (such as cardiovascular diseases, cancers, etc.) to environmental exposure factors, especially air pollutants, heavy metals, and food-borne pathogens factors. Risk assessment has also been a category of interest in recent years.
Conclusion: Scientometric analysis showed that environmental health studies in prevention and control of diseases related to environmental factors in Iran are young and still progressing. In the early years, studies were mainly focused on diseases as an outcome, while in recent years, they have focused more on exposure factors or environmental pathogens. It is suggested that the future studies based on the retrieved keywords should be more mission-oriented and the priority of solving the problems of environmental pollutants affecting people's health in the country based on the extent and scope of the problems of each province should be considered by policy makers and researchers.