Judul: Penentuan Ambang Batas Nilai Ekstrem dan Pendugaan Parameter pada Sebaran Pareto Terampat
Abstrak: Teorema Nilai Ekstrem adalah metode yang secara khusus membahas kejadian-kejadian ekstrem. Salah satu cara dalam penentuan nilai ekstrem, diantaranya menggunakan Mean Excess Plot (MEP), yaitu dengan menentukan nilai ambang batas u kejadian ekstrem berdasarkan sebaran Pareto Terampat (Generalized Pareto Distribution, GPD). Pemilihan ambang batas dilakukan berdasarkan linieritas MEP, walaupun umumnya tidak mudah dan sedikit subjektif. Pada penelitian ini untuk menduga nilai parameter bentuk dari sebaran GPD yang dihasilkan MEP digunakan plot Hill, plot Pickands, dan slope atau koefisien kemiringan plot Q-Q. Plot penduga parameter dipilih ketika pola terlihat stabil. Data simulasi yang dibangkitkan dengan mengikuti sebaran GPD menunjukkan bahwa metode MLE dan Pickands lebih baik dalam pendugaan parameter bentuk dibandingkan dengan Hill dan plot Q-Q berdasarkan nilai MAPE yang kecil dan hasil dugaan parameter bentuk yang semakin baik jika nilai parameter bentuk mendekati satu. Untuk data riil, nilai ambang terbaik pada data curah hujan bulanan di stasiun curah hujan Indramayu adalah 340 mm, yang dipilih berdasarkan dugaan parameter bentuk yang konsisten dengan 0< <1.
Keyword: EVT, GPD, MEP

Judul: Pendugaan Nilai Ekstrim Menggunakan Sebaran Champemowne Termodifikasi, Sebaran Pareto Terampat, dan Nilai Gabungan (Studi Kasus Curah Hujan Harian Darmaga Bogor)
Abstrak: Extreme rainfall can give a negative affect for human activity. Negative effect of production failure in agriculture and plantations can be anticipated by extreme rainfall estimation that may occur in the future. The aims of this study is to compare the extreme rainfall estimation using the modified Champernowne distribution and generalized Pareto distribution (GPD), and determine the optimum weights of combined extereme value estimation. Modified Champernowne distribution patern has convergence to the GPD that the distribution function consists of three parameters that describe the data center, the diversity, and characteristics of the end of the distribution. While GPD consists of two parameters that describe the diversity and characteristics of the end of the distribution (heavy tail/tail light). The data used are daily rainfall data in Darmaga Bogor Station during the period 1985-June 2011 were obtained from the Indonesian Agency for Meteorology Climatology and Geophysics. GPD estimation tends to over estimate while modified Champernowne distribution estimation tends to under estimate. The combine of the estimated value by weighted produces more accurate extreme value estimation. Forecasting results for 1, 2, and 3 month ahead show that the best prediction based on modified Champernowne distribution, while forecasting results for 6 and 9 month ahead is very well predicted by GPD and combined value.
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Judul: Hydroxyapatite-Chitosan Composite Coating on Stainless Steel 316 to Improve Corrosion Resistance
Abstrak: Metals that were used in bone implantation should have good corrosion resistance that were not easily corroded when implanted into the body. Metal corrosion resistance of stainless steel 316 can be enhanced through the metal coating by hydroxyapatite-chitosan composite with composition ratio of hydroxyapatite (gram) and chitosan 3% (mL) 0.2:0, 0.2:0.1, 0.2:0.5, 0.2:1.0, and 0.2:1.5. Besides improving the corrosion resistance of metal, the presence of chitosan also maintain the position of hydroxyapatite on metal surfaces. Corrosion resistance increases with increasing amount of chitosan added and the best composition of hydroxyapatite-chitosan composite was 0.2:1.0.
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