Judul: Pengaruh Lama Penyimpanan dan Perebusan Daun Sirsak Segar (Annona muricata Linn) terhadap Aktivitas Antioksidan Sari Daun Sirsak.
Abstrak: Soursop (Annona muricata Linn) leaves have been used as traditional medicine. Antioxidant compounds contained in the soursop leaves are steroids or terpenoids, flavonoids, coumarins, alkaloids, saponins and tannins. The objectives of this research was to assess effect of storage time (0, 3, 7 and 14 days) at low temperature (4-8oC) and boiling time (5, 7 and 10 minutes) of fresh soursop leaves with boiling water (98oC) on antioxidant activity of soursop leaves extract. Analysis performed to the extracts were water content, pH, antioxidant activity (DPPH method), total phenolics and total flavonoids. The results analysis of variance showed that soursop leaves storage and boiling time gave significant (α<0.05) impact to antioxidant activity, total phenolics, total flavonoids and pH values. Fresh soursop leaves that stored in low temperature (4-8oC) longer have lower average value of antioxidant activity, total phenolics and total flavonoids of soursop leaves extract, but higher average value of pH. Moreover, longer boiling time resulted to higher average value of antioxidant activity, total phenolics and total flavonoids extract of soursop leaves, but lower average value of pH. The best treatment is based on the highest value of antioxidant activity, obtained from soursop leaves storage time treatment of day-zero with boiling time 10 minutes.
Keyword: Annona muricata Linn, antioxidant, boiling time, storage time

Judul: Pengaruh Ph Larutan Penyeduh Dan Lama Penyeduhan Terhadap Kapasitas Antioksidan Ekstrak Teh Daun Sirsak (Annona Muricata Linn)
Abstrak: Daun sirsak memiliki kandungan fitokimia antioksidan yang tinggi. Di Indonesia air rebusan daun sirsak telah digunakan sebagai obat tradisional. Pada penelitian ini, daun sirsak diolah menjadi bentuk teh untuk meningkatkan kestabilannya selama penyimpanan. Penelitian ini bertujuan unuk mengkaji pengaruh pH larutan penyeduh (6, 4 dan 3) dan lama penyeduhan (5, 7.5, 10 dan 12.5 menit) terhadap kapasitas antioksidan, total fenolik dan total flavonoid dari ekstrak teh daun sirsak. Hasilnya menunjukkan bahwa kapasitas antioksidan dan total flavonoid pada larutan peyeduh pH 6 lebih besar daripada pH 3 dan 4 (p<0.05), sedangkan total fenolik tidak dipengaruhi pH larutan penyeduh (p>0.05). Lama penyeduhan (5, 7.5, 10 dan 12.5 menit) tidak berpengaruh nyata (p>0.05) terhadap kapasitas antioksidan, total fenolik dan total flavonoid yang diduga karena penurunan suhu selama penyeduhan mengakibatkan proses ekstraksi kurang efektif.
Keyword: antioksidan, lama penyeduhan, pH ekstraksi, teh daun sirsak

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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