Judul: Pendekatan Matematis pada Pembangkitan Gelombang Internal di Selat Makassar
Abstrak: Di selat Makassar, yang terletak di antara pulau Kalimantan dan Sulawesi, fenomena gelombang internal yang menakjubkan dapat diamati. Gelombang internal adalah gelombang gravitasi yang berosilasi di dalam, bukan di permukaan, media fluida. Gelombang internal terjadi di bagian dalam air di laut, yang terjadi karena perbedaan densitas lapisan bawah dan atas fluida. Karakteristik khas gelombang internal adalah panjang gelombang dan amplitudonya yang besar. Penelitian ini bertujuan untuk mendapatkan hubungan dispersi berdasarkan persamaan dasar fluida dua lapis, menentukan gelombang internal di Selat Makassar, dan membuat simulasi pembangkitan gelombang internal menggunakan perangkat lunak Mathematica. Hasil penelitian menunjukkan bahwa mekanisme pembangkitan gelombang internal ini dapat dirumuskan berdasarkan hubungan dispersi Kelvin-Helmholtz untuk fluida dua lapis. Relasi dispersi ini juga dapat digunakan sebagai kriteria klasifikasi ketidakstabilan gelombang internal. Penekanan diberikan pada jenis ketidakstabilan, yaitu ketidakstabilan temporal dan spasial. Stabilitas temporal terjadi jika kecepatan arus di bagian atas fluida kurang dari kecepatan kritisnya. Untuk ketidakstabilan spasial, gelombang internal di Selat Makassar dapat didekati untuk kedua lapisan sebagai gelombang laut dalam. Daerah stabil spasial tercapai ketika frekuensi bagian bawah fluida lebih kecil dari frekuensi kritis, atau ketika frekuensi bagian atas fluida lebih besar dari frekuensi kritis.
Keyword: Makassar strait, generation of internal waves, instability

Judul: Pendekatan matematis pada pembangkitan gelombang internal di Selat Makassar
Abstrak: In Makassar strait, which is located between the islands of Kalimantan and Sulawesi, the fascinating phenomena of internal waves can be observed. Internal waves are gravity waves that oscillate within, rather than on the surface of, a fluid medium. Internal waves occur in the interior of water in seas, which exist due to a difference in density of the lower and upper layer of the fluid. Typical characteristics of internal waves are their large wavelength and amplitude. This research aims to derive a dispersion relation based on the basic equations of two-layers fluid, to determine the internal waves in the Makassar Strait, and to create a simulation of generation of the internal waves using the software Mathematica. The results show that the generation mechanism of these internal waves can be formulated based on the Kelvin-Helmholtz dispersion relation for a two-layers fluid. This dispersion relation can also be used as classification criteria of instability of internal waves. Emphasis is given to the types of instability, i.e. temporal and spatial instability. Temporal stability occurs if current velocity in the upper part of fluid is less than its critical velocity. For the spatial instability, internal waves in Makassar strait can be approximated for both layers as deep water waves. The spatially stable region is reached when the frequency of the lower part of fluid is smaller than the critical frequency, or when the frequency of the upper part of fluid is larger than the critical frequency.
Keyword: Sea current, Generation of internal waves, Pycnocline

Judul: Penapisan Inhibitor Tirosinase pada Empat Spesies Famili Asteraceae Chrysantemum morifolium R, Gerbera jamesonii A, Dahlia rosea Cav, dan Tagetes erecta.
Abstrak: The research was conducted to screen the potency of tyrosinase inhibitor from 4 species of Asteraceae family. The screening was performed on the leaves and flowers of Chrysantemum morifolium R, Gerbera jamesonii A, Dahlia rosea Cav, and Tagetes erecta. The samples were dried and then extracted with nhexane, ethyl acetate, and methanol. The inhibition activity was tested by a microplate reader spectrophotometer in 492 nm. The ethyl acetate extract of D. rosea Cav flower was the most potent tyrosinase inhibitor (IC50 for monophenolase 18.42 μg/mL and for diphenolase 687.79 μg/mL) compared with the other Asteraceae species. The most active essential oils as inhibitor of tyrosinase was obtained from T. erecta flower (IC50 for monophenolase 1882.62 μg/mL and for diphenolase 1884.33 μg/mL). Positive control used was kojic acid with IC50 value of 11.02 μg/mL for monophenolase and 84.19 μg/mL for diphenolase. Fractionation of the extract by preparative thin layer chromatography with chloroform as mobile phase gave 12 fractions. The most active fraction had IC50 of 5.55 μg/mL for monophenolase and 109.96 μg/mL for diphenolase, and was identified as flavonoid.
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