Judul: Pengaruh perendaman umbi singkong dalam larutan asam asetat terhadap karakteristik mutu keripik singkong
Abstrak: Processing modification of cassava tubers is expected to produce the cassava chips with specific quality characteristics. One form of the modification process is by using acetic acid as medium of soaking of cassava tubers. This study was aimed to know the effects of soaking of cassava tubers in acetic acid solution on quality characteristics of cassava chips. The treatments of this research were soaking cassava tubers in acetic acid solution with concentrations of 0.5; 1.0; 2.0 and 3.0 for 2 hours; 4 hours; and 6 hours. Soaking of cassava tubers in acetic acid solution for 2 hours and 4 hours resulted cassava chips with the lowest brittleness and hardness. Then, soaking treatments of cassava tubers in acetic acid solution with concentrations of 0.5 and 1.0 for 0.5 hour; 1 hour; 1.5 hours; and 2 hours showed that cassava chips with soaking treatment in acetic acid solution for 0.5 hour and 1.5 hours resultedthe lowest brittleness. Organoleptic test showed that cassava chips with soaking treatment in acetic acid solution with concentration of 1.0 for 1.5 hours had the greatest sensory value and be the best cassava chips. The soaking treatment in acetic acid solution acid has produced cassava chips with specific quality characteristics, such as brighter on colors, reduced bitter taste, flavor was preferred, and the texture wasn’t harder. The best cassava chipswas stored for 4 weeks in polypropylene plastic packaging at room temperature. The brightness ofboth of cassava chips with soaking treatment inacetic acid solution with concentration of 1.0 for 1.5 hours (the sample) and cassava chips without acetic acid soaking treatment (control) increased during storage. The increased of brightness was also followed by a decreased in the value of a and b. The rate of increase in the value of brittleness and hardness in the sample were greater than that of control. The sensory value for sample and control decreased, and it showed the decreased of quality characteristics of cassava chips during storage. Up to second week of storage, the peroxide value of sample was greater than that of control. The peroxide value of sample increased at greater rate than that of control during storage.
Keyword: Bogor Agricultural University (IPB), peroxide value., chips, cassava, acetic acid

Judul: Pengaruh Perlakuan Panas sebelum Penggorengan terhadap Kerenyahan
Abstrak: Cassava is one of the local commodities of Indonesia that can be found easily at many places. Cassava chip is one of the popular snacks in Indonesia and crispness becomes one of the important factors to measure cassava chips quality. Some efforts have been tried to enhance the crispness of cassava chip. Heating processes before frying, such as steaming and boiling, are explored whether they can help to enhance cassava chip crispness or not. Steaming and boiling can cause the cassava starch gelatinization. As a result, the starch granule swells because of water hydration. When cassava slices is fried, the water comes out and small pores formed. The pores can cause the crispness of chips. The crispness was analyzed by sensory evaluation using rating and triangle test as subjective test and physical test using texture analyzer as objective test. Proximate analysis was also done to see if there are any effects of nutrients change because of heating processes to crispness. The result showed that steaming and boiling cassava slices before frying enhanced the crispness of cassava chips. Nutrients changed because of these heating processes.
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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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