Judul: Penggunaan Pgfpuv Mutan Untuk Mempelajari Pengaruh Pengeringan Pada Ketahanan Hidup Cronobacter Sakazakii Dalam Jagung.
Abstrak: Cronobacter sakazakii adalah bakteri patogen emerging penyebab penyakit meningitis dan necrotizing enterocolitis pada kelompok bayi tertentu. Beberapa C. sakazakii telah diisolasi dari sumber pangan di Indonesia dan transformasi dengan plasmid yang menyandi Green Fluorescent Protein (GFP) telah menghasilkan mutan C. sakazakii pGFPuv dengan pola pertumbuhan serupa dengan galur wild type-nya. Penelitian ini bertujuan untuk memanfaatkan C. sakazakii pGFPuv untuk mempelajari pengaruh pengeringan terhadap kadar air dan aktivitas air jagung serta sintasan (survival) C. sakazakii pada jagung. Jagung pipil dengan kadar air 40% (b.k) diinokulasi dengan C. sakazakii pGFPuv sehingga konsentrasi awalnya CFU/g dan dikeringkan pada suhu 42 ºC, 46 ºC dan 50 ºC selama sepuluh hari. Setiap hari, sampel jagung diambil untuk diukur kadar airnya dengan menggunakan metode oven, aktivitas airnya dengan Aw meter, serta dienumerasi Total Plate Count dan C. sakazakii yang bertahan dengan metode pemupukan agar cawan. Disamping itu, sampel terpilih dari pengeringan 50oC diamati dengan Scaning Electron Microscopy (SEM). Tingkat sintasan C.sakazakii selama pengeringan ditentukan dari kemiringan regresi linier kurva sintasan C.sakazakii. Hasil penelitian menunjukkan bahwa jumlah C. sakazakii turun dengan cepat pada fase laju penurunan k.a/aw cepat dan lebih lambat pada laju saat penurunan ka/Aw lambat. Pada fase lambat, C. sakazakii cenderung lebih mampu bertahan dibandingkan dengan total bakteri.. Aw kritis untuk bakteri patogen adalah antara 0.85-0.86. Pengamatan dengan SEM menunjukkan bahwa C. sakazakii pGFPuv membentuk koloni pada permukaan dan pada bagian tip cap jagung. Penelitian ini menunjukkan bahwa mutan C. sakazakii pGFPuv dapat digunakan untuk mempelajari sintasan C. sakazakii selama pengeringan jagung. C. sakazakii dapat bertahan pada pengeringan jagung suhu 42 ºC, 46 ºC dan 50 ºC selama sepuluh hari.
Keyword: Cronobacter sakazaki, pGFPuv, jagung, sintasan, pengeringan, aktivitas air

Judul: Penggunaan pGFPuv Mutan Untuk Mempelajari Pengaruh Pengeringan Pada ketahanan hidup Cronobacter sakazakii Dalam Jagung.
Abstrak: Cronobacter sakazakii is an emerging Gram-negative foodborne bacterial pathogen regarded as the causative agent of meningitis and necrotizing enterocolitis in certain groups of infants. Several isolates of C C. sakazakii have been obtained from food samples in Indonesia and transformation with a Green Fluorescent Protein (GFP) plasmid has produced C. sakazakii pGFPuv mutants with growth pattern similar to that of the wild-type strains. Therefore, they are potential to be used for studying C. sakazakii behaviour without the need to suppress other microorganisms and the use of diagnostic media. The research activities focused on the following objectives : to study the effect of drying on water content and water activity of maize and to evaluate the survival of C. sakazakii pGFPuv as well as other naturally occurring microorganisms in maize during drying. Maize kernels with moisture content of 40% (d.b) were inoculated with C. sakazakii pGFPuv mutant such that the initial concentration in the maize was CFU/g and drying was performed at temperatures of 42 ºC, 46 ºC and 50 ºC for ten days in a drying chamber. Every day the maize samples were taken and the water content were analyzed using oven method while water activity by Aw meter. Total Plate Count and C. sakazakii surviving in the maize were enumerated by standard plate count. The survival rate of C. sakazakii during drying was determined by the slope of linear regression from C. sakazakii survival curve. The results showed that the fate of decrease of C. sakazakii during the rapid decline of water content and Aw can be divided into three phases, i.e. logarithmic decrement, static growth and the final decline. The critical water activity for these pathogenic bacteria was in the range of 0.85-0.86. Observation by SEM showed that C. sakazakii GFPuv form colonies on the surface of corn and the tip cap. This study showed that of C. sakazakii pGFPuv can be used to study the survival of C. sakazakii during corn drying.
Keyword: Cronobacter sakazaki, pGFPuv, maize, survival, drying, water activity

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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