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"The utilization of bricks made of styrofoam is expectedly able to be a soundproof for noise control and as a preventive action to reduce the steadily increasing prevalence of hearing loss. This study aimed to assess the use of sound absorption material in which styrofoam was utilized to reduce the noise exposure. In this study, fine aggregates (sand and styrofoam) were made with a mixture of cement with a composition of 1:4 and 1:6, also the addition of polystyrene waste with a percentage of 0%, 20%, 40%, 60%, and 80%. Determination of acoustical property of the mixture was done by testing the sound absorption coefficient using Four Microphones Impedance Tube (ISO 140-3). The results showed that the highest value of absorption coefficient was at a frequency of 800 Hz with an additional 80% styrofoam for the composition of 1:4 at 0.4100 dB and at a frequency of 800 Hz with an additional 40% styrofoam for the composition of 1:6 at 0.5870 dB."

"Perhitungan sifat optik material berupa absorpsi atau penyerapan cahaya pada semikonduktor sering dilakukan dengan menggunakan asumsi dispersi energi kuadratik (parabola) di kedua pita energi valensi dan konduksi. Namun, pendekatan tersebut tidak cukup realistis, mengingat bentuk pita energi yang kita temui pada material tidak selalu mengikuti pendekatan kuadratik. Oleh karena itu, pada penelitian kali ini, kami menyelidiki pengaruh dari beberapa bentuk pita energi pada penyerapan cahaya di material semikonduktor. Secara khusus, spektrum penyerapan cahaya dihitung untuk material semikonduktor hipotetis dengan bentuk pita energi kuadratik (parabolik) dan nonparabolik seperti kuartik (pangkat empat) dan sekstik (pangkat enam). Kami juga mempertimbangkan efek dimensi material (dari satu hingga tiga dimensi) lalu membandingkan hasil yang telah dihitung. Untuk mendukung model tersebut, kami kemudian menghitung penyerapan cahaya secara numerik menggunakan pendekatan density functional theory (DFT) dari beberapa representasi material yang kami temukan memiliki bentuk dispersi energi yang serupa dengan yang model yang diajukan, seperti PtS2 dan GeTe. Kami menemukan dalam semikonduktor hipotetis untuk perhitungan sepasang pita energi yang sama, efek dimensi memengaruhi hasil penyerapan cahaya, semakin tinggi dimensinya, semakin tinggi penyerapan cahaya yang kami dapatkan. Untuk perhitungan pita kombinasi, tidak hanya dimensi yang memengaruhi absorpsi, tetapi juga bentuk pita konduksi dan pita valensinya. Kami menemukan bahwa material PtS2 memiliki hasil yang mirip dengan penyerapan cahaya untuk kombinasi pita nc = 2 dan nv = 4. Dan untuk GeTe kami menemukan bahwa hasilnya berbeda dengan kombinasi nc = 2 and nv = 4.

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Calculations of optical properties such as the light absorption of semiconductors are often performed by assuming parabolic energy dispersion of both valence and conduction energy bands. However, this approach is not quite realistic, because the actual shape of the energy bands often deviates from the quadratic shape. Therefore, we need to investigate the effect of a more realistic shapes of electronic band structures on light absorption in semiconducting materials. In this study, the absorption spectra are calculated for hypothetical semiconductors with higher degree polynomial, i.e. quartic (fourth-degree polynomial) and sextic (sixth-degree polynomial) energy dispersion. We also consider one to three dimensional cases and compare the calculated spectra. To validate our model, the calculated spectra are compared with some representative materials having similar band shapes, such as Si, PtS2, and GeTe. In this case, the light absorption is calculated numerically using a first-principles, density functional theory approach. We found in the hypothetical semiconductor for band pair transition, its dimension affects the light absorption. Higher dimensions have larger light absorption. The calculations also show that the transition between bands is affected by not only the material’s dimension, but also the shape of the conduction band and valence band. We found that the light absorption of material PtS2 is similar to the calculated light absorption that corresponds to a transition of band nc = 2 to nv = 4. Meanwhile, GeTe’s light absorption deviates from such an optical transition."