Judul: Aktivitas Antioksidan Ekstrak Pelepah Pohon Aren (Arenga pinnata Merr.)
Abstrak: Stem sugar palm has been reported to contain tannin compound, however, there is no scientific information about its potential as antioxidant. Hence, the objective of this research was to measure the antioxidant activity of stem sugar palm extract (Arenga pinnata Merr.) in vitro. This research used water, ethanol 70% and ethanol 96% as solvents. The stem sugar palm was extracted in water solvent by boiling method and by maceration in ethanol 70% and 96% solvents. Bioactive compounds in the extracts were determined by phytochemical method. Antioxidant activity of stem sugar palm extracts were determined by 1,1-diphenyl-2-picrylhydrazyl radical absorption method (DPPH) and the content of the total phenolic measured in colometric with Folin-Ciocalteu method. The result showed that the stem sugar palm extracts contained saponin, tannin and phenol, and steroids and triterpenoid. Analysis of antioxidant activity showed that both ethanol 70% and 96% stem sugar palm extracts were potential as natural antioxidant. The highest antioxidant activity and the total phenolic value were showed by ethanol 96% extract (IC50 = 2.570 μgL-1; 3.75 GAE mgg-1).
Keyword: phenolic, phytochemical, stem sugar palm, DPPH, Antioxidant

Judul: Aktivitas Antioksidan Ekstrak Etanol Daun Serai (Cymbopogon citratus) dan Potensinya Sebagai Pencegah Oksidasi Lipid
Abstrak: Cymbopogon citrates is usually used as spices by Indonesian people. The utilization of lemongrass is only limited on it stem, but the leaf remain as waste. The aim of this research was to analyze phytochemical components and to determine the phnolic content and antioxidant assay with ethanol solvent each 30%, 70% and 96%. The extraction of lemongrass leaf was performed by maceration. The result of phytochemical analysis indicated that the ethanolic extract of lemongrass leaf contains alkaloid, saponin, tannin, flavonoid, phenol and steroid. The phenol content determination was performed by Folin- Ciocalteau method with the highest phenolic content was obtained on ethanolic extract 30% was 50.017 GAE (Gallic Acid Equivalent) mg/g. The ethanol extract of lemongrass leaves through its inhibitory potency as an antioxidant against free radical DPPH (2,2-diphenyl-1-pikrylhydrazyl) with with the highest IC50 on 70% ethanol was 79.444 mg/L. The antioxidant activity on lipid system with rancimat method was obtained on 70% ethanol as 1.19 and the longest induction time was 6.15 hours.
Keyword: Bogor Agricultural University (IPB), DPPH., rancimat, total phenolic, antioxidant, lemongrass leaf

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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