Judul: Pemanfaatan Kulit Mete sebagai Arang Aktif Penyalut Urea dan Pengujiannya terhadap Tingkat Kehilangan Nitrogen pada Urea
Abstrak: Cashew shell (Anacardium occidentale) is agricultural waste that can be used as activated carbon material. Activated carbon from cashew shell, which is physically activated, could comply with the Indonesian Standard (SNI). In this research, degree of nitrogen reduction in urea which was coated with various particle size of activated carbon (60, 80, and 100 mesh) and comparison between activated carbon and urea (30:70, 20:80, 10:90) were studied. The best result of the coated urea was using of 100 mesh with composition of activated carbon:urea 30:70. The activated carbon as a coating material for urea caused the decreasing of evaporation from 0.22% to 0.03% with efficiency value of 86.36%. Meanwhile, the amount of nitrogen in urea that dissolved in water after solubility and cracked tests decreased from 52.99% to 38.10% with efficiency value of 28.10%. The volume of percolate decreased together with the increasing of soil amount, the presence of urea coated by activated carbon, and the reaction time. According to the data, the coated urea using activated carbon from cashew shell is effective to increase the efficiency of urea application for agricultural purposes.
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Judul: Slow Release N-Urea dalam Bentuk NH4+ dan NO3- setelah Aplikasi Arang Aktif pada Tanah Andisol
Abstrak: Urea is fertilizer that has low efficiency absorption in soil-plant system, which is about 30-50%. This is due to highly hygroscopic nature of urea that made urea dissolve easily into groundwater as nitrate when it applied to plants. Slow release fertilizer releases essential nutrient contained in urea slower than original urea fertilizer. Agriculture waste could be used as activated carbon which used to coat the urea in order to make slower release. The activated carbon in this study functioned in two different ways, as a coating material for the urea and as an adsorbent of urea residue. The research aimed to compare decreasing efficiency of dissolved urea as NH4+ and NO3- in Andisol soils using four activated carbon materials: coconut shells, rice hulls, corn cobs, and palm empty bunch during incubation period of 30 days. The result pointed out that the activated carbon could decrease NH4+ and NO3- dissolved in soil about 4-44% as compared with the control soils. It also showed that the activated carbon was the most effective in decreasing dissolved NH4+ and NO3- were those derived from coconut shells and rice hulls.
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Judul: Dynamical System of Hepatitis B in Three Groups with Vaccination
Abstrak: The aim of this study is to modify the hepatitis B transmission model in three age groups involving vaccination from the model conducted by Zhoe and Zhang.The method used is to analyze the stability of the fixed point and its basic reproduction number (R_0). Performed stability analysis and numerical simulation to see population dynamics. Next, a sensitivity analysis of the parameters was carried out to see its effect on R_0. From the analysis obtained two fixed points, namely non-endemic and endemic fixed points. Non-endemic fixed points are locally asymptotically stable if R_0 <1 Meanwhile, the endemic fixed point is locally asymptotically stable if R_0 > 1. Hepatitis vaccination affects the number of susceptible population, because the more successful the vaccination, the smaller the number of susceptible populations so that the smaller the population will be infected.
Keyword: Dynamic, Hepatitis B, Vaccine, Mathematical model