Judul: Kajian Aktivitas Antimikroba Ekstrak Belalang terhadap Bakteri E. coli dan S. aureus serta aplikasinya pada bakso daging
Abstrak: Javanese grasshopper (Vangala nigricornis) is one of various insects that grows in Indonesia. Beside to its nature is destructive and considered crop pests for farmers, Javanese grasshopper used as food for some people, particularly in Wonosari Jogjakarta. In addition to the useful as food, Javanese Grasshoppers also capable of inhibiting the growth of pathogenic bacterias, that are E. coli and S. aureus. The aim of this research was to find out the Javanese grasshopper as a preservative in fact, meat products. Research prefixed to prove the existence of the antimicrobial activity from Javanese grasshopper by using the well diffusion method. Extract derived from four solvents, that were water, ethanol, acetic acid, and hexan. From four extracts was got, extract acetic acid (± 9 mm) and extract ethanol (± 7 mm) that showed antibacterial activity. Next step was to determined the minimum inhibitory concentration of the extract was selected (acetic acid), which amounted to 6 %. The last step was to test to meatball products, from this test known the extracts Javanese grasshopper able to extend the life of stored meatballs than meatballs control.
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Judul: Potensi Antimikroba Kayu Siwak (Salvadora persica Wall.) terhadap Staphylococcus aureus dan Pseudomonas aeruginosa serta Aplikasi pada Bakso Daging
Abstrak: Preservation of processed meat products have been carried out with the aim of extending the shelf life. Preserving is one important factor considering the risks that may be posed and one of them is the use of hazardous chemicals as preservatives. One of food product which is vulnerable given the addition of formalin was the meatball. Siwak has been known to have antimicrobial activity but its application for foods has not been widely explored. The study consist of four phases, extraction of siwak well diffusion test, dillution broth to determine MIC, and applications in meatballs. Well diffusion test showed that siwak’s extract has antimicrobial activities against Staphylococcus aureus bacteria and Pseudomonas aeruginosa bacteria which have inhibition zones of 21.10 mm and 20.11 mm respectively. Dillution broth test showed that the minimum concentration which is can inhibit bacterial growth was 50% (v/v) of siwak’s aqueous extract. Application in meatballs showed that siwak extract can hold down bacterial growth up to 98,17% in Staphylococcus aureus bactery.
Keyword: natural preservative., antimicrobial activity, siwak, preservation

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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