Judul: Aktivitas Antioksidan dan Inhibisi Enzim α Glukosidase serta Toksisitas Ekstrak Air-Etanol dan Heksan Anggrek Merpati (Dendrobium cruminatum SW)
Abstrak: Dendrobium cruminatum are anggrek that grow in almost all regions of Indonesia. Dendrobium cruminatum leaves contain flavonoid compounds that are useful as an antioxidant and antidiabetic. This study aims to determine the ability of the anggrek merpati extract as an antioxidant and it’s potential to inhibition activity of α-glucosidase enzyme and also as a compound that toxic to the larvae of shrimp Artemia salina Leach with different solvents. The antioxidant activity was measured by using DPPH method and antidiabetic measured by the formation of p-nitrifenol-α-D-glukopiranosida (p-NPG) were measured with a spectrophotometer at a wavelength of 410 nm. The results of antioxidant activity and cytotoxicity testing showed that the best solvent used for the extraction of anggrek merpati leaf is water solvent with IC50 value of 153.565 μg / mL and the level of cytotoxicity was 889.641 mg / mL. whereas the activity of the inhibition of α-glucosidase enzyme is owned by the highest percentage of etanol by 64% at a concentration of 1000 μg / mL or IC50 value of 435 μg / mL.
Keyword: Bogor Agricultural University (IPB), antidiabetic and cytotoxicity., antioxidant, Dendrobium cruminatum

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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