Judul: Aktivitas antioksidan serta korelasinya dengan kadar fenol, flavonoid, dan antosianin total pada enam spesies Rhododendron
Abstrak: Rhododendron diketahui bermanfaat bagi kesehatan, salah satunya sebagai antioksidan. Tumbuhan Rhododendron asal Indonesia yang digunakan pada penelitian ini terdiri atas R. javanicum, R. retusum, R. malayanum, R. konori, R. seranicum, dan R. jasminiflorum. Aktivitas antioksidan ditentukan menggunakan metode 2,2-difenil-1-pikrilhidrazil (DPPH), ferric reducing antioxidant power (FRAP), dan cupric ion reducing antioxidant capacity (CUPRAC). Hasilnya menunjukkan metode yang digunakan menghasilkan nilai kapasitas antioksidan yang berbeda nyata secara analisis ragam. Bagian batang R. retusum memiliki kapasitas antioksidan tertinggi, yaitu 36.68 µmol troloks/g serbuk kering dengan menggunakan metode DPPH. R. konori bagian daun memiliki aktivitas antioksidan tertingi, yakni 941.76 dan 1793.62 µmol troloks/g serbuk kering masing-masing dengan menggunakan metode FRAP dan CUPRAC. Kadar fenol total berkorelasi signifikan dengan aktivitas antioksidan sedangkan kadar flavonoid dan antosianin total memiliki korelasi yang tidak signifikan.
Keyword: antioxidant activity, Rhododendron, total anthocyanin, total flavonoid,

Judul: Pengukuran Aktivitas Antioksidan dengan Metode Cuprac, DPPH, dan Frap serta Korelasinya dengan Fenol dan Flavonoid pada Enam Tanaman
Abstrak: Oxidative stress is the imbalance condition between free radical and antioxidants that can cause oxidative damage in cell, tissues, organ, accelerates the aging process, and emergence of diseases. This study aims to determine the antioxidant capacity of 6 herbs, and the relationship between phenol and flavonoids content with their antioxidant activity and relationship between phenol and flavonoids content in the ethanol extract of some Indonesian herb, there are Orthosiphon stamineus, Sonchus avensis, Sida rhombifolia, Guazuma umifolia, Andrographis paniculata, and Parkia biglobosa. The measurement of antioxidant activity use 3 methods, that are CUPRAC (cupric ion reducing antioxidant capacity), DPPH (2,2-diphenyl-1-pickrylhidrazyl), and FRAP (ferric reducing antioxidant power). The research of the six herbs showed antioxidant activity. Statistic test from three method antioxidant showed that measurement antioxidant activity with CUPRAC, DPPH, and FRAP gave a significantly different result, but CUPRAC and FRAP give the same response of the six herbs. The phenol has no correlation with flavonoids content but have highly correlation with their antioxidant activity. Flavonoids have no correlation with antioxidant activity.
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Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
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