Judul: Model Prediktif Pertumbuhan Staphylococcus aureus pada Rendang Daging Sapi
Abstrak: Model mikrobiologi prediktif merupakan model matematika yang digunakan untuk mengetahui pertumbuhan mikroorganisme serta responnya terhadap kondisi lingkungan sehingga dapat diketahui populasinya. Rendang merupakan salah satu makanan tradisional khas Sumatera Barat. Makanan ini terbuat dari daging sapi yang dimasak selama 4 hingga 5 jam bersama dengan santan, bawang putih, bawang merah, dan rempah-rempah lainnya. Proses pemasakan rendang serta tambahan rempah-rempah seharusnya dapat meminimalisir cemaran bakteri pada rendang, namun masih ada korban keracunan akibat rendang. Tujuan dari penelitian ini adalah untuk menentukan parameter kinetik pertumbuhan S. aureus pada rendang daging dengan menggunakan model prediktif pada berbagai suhu penyimpanan, dan menyusun kurva pertumbuhan S. aureus pada rendang daging. Suhu penyimpanan yang digunakan adalah 26, dan 35°C. Model primer yang digunakan adalah model Huang, Baranyi dengan h0, Baranyi bebas h0, dan modifikasi Gompertz sedangkan model sekunder yang digunakan yaitu model Ratkowsky. Hasil penelitian menunjukkan bahwa suhu penyimpanan rendang daging sapi terbaik yaitu pada suhu ruang (26°C) karena tidak ditemukan pertumbuhan pada suhu rendah. Berdasarkan hasil penelitian, dapat disimpulkan bahwa model modifikasi Gompertz memiliki hasil fitting kurva terbaik.
Keyword: Kurva pertumbuhan, Model prediktif, Rendang daging sapi, growth curve, modified Gompertz model, predictive model, rendang beef

Judul: Pendugaan Pertumbuhan Staphylococcus aureus pada Sosis Ayam Dengan Penyimpanan Dingin Menggunakan Response Surface Methodology
Abstrak: This research studied the effect of low temperature (-5, 2.5, and 10 °C) and the initial member of S. aureus (0 to 100 cfu gram-1) on the growth curve of S. aureus in chicken sausage, in order to determine the growth rate and lag phase model of S. aureus. The data were plotted and fitted using Response Surface Methodology (RSM) to obtain the growth models of the bacteria under defined conditions. Steps of the study included sample preparation (preparation and confirmation of inoculum following by inoculation of S. aureus cultures on chicken sausage samples), determining the growth pattern of S. aureus ATCC 25923 in chicken sausage at storage temperature 35-37 ºC and 25-30 ºC for 24 hours, as well as at -5 to 10 ºC for 1 to 2 week. The data were then proced using RSM to obtain modelling, model validation, and growth curves plotting based on the Baranyi equation. Growth rate of S. aureus (cfu gram-1 day-1) with concentration factor 0, 20, dan 100 cfu gram-1 and storage temperature -5 until 10 °C in BPA + egg yolk tellurite is y = 0.0093 + 0.0158 temperature + 0.0011 concentration + 0.0003 temperature *concentration. R2 0.60 with confident level 95%. Lag time of S. aureus (day) with concentration factor 0, 20, dan 100 cfu gram-1 and storage temperature -5 until 10 °C in BPA + egg yolk tellurite is y = 0.1680 + 0.0193 temperature + 0.2857 concentration + 0.0052 temperature*concentration. R2: 0.58 with confident level 95%.
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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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