Judul: Fluktuasi Ketinggian Tropopause Tropis Dengan Menggunakan Analisis Komponen Utama Dan Spektral
Abstrak: Data ERA-Interim ECMWF dengan parameter ketinggian geopotensial level 100 mb di kawasan tropis selama 30 tahun (Januari 19981 – Desember 2010) digunakan untuk mengidentifikasi fluktuasi tinggi tropopause kawasan tropis. Pola – pola fenomena pembangkit fluktuasi ketinggian tropopause di wilayah kajian teridentifikasi dengan menggunakan metode Analisis Komponen Utama (PCA), analisis spektrum, dan analisis spektrum silang. Tiga komponen utama mampu merepresentasikan 90.4% dari variabilitas total fluktuasi ketinggian tropopause di wilayah tropis. Analisis spektral pada ketinggian komponen utama menunjukkan bahwa fluktuasi ketinggian tropopause tropis didominasi oleh periode 12 bulan dan 45 bulan yang merupakan variasi insolasi orbital dan El Niño-Southern Oscillation (ENSO), sedangkan fenomena lainnya Quasi-Biennial Oscillation (QBO) dan Madden-Julian Oscillation (MJO). Fenomena tersebut memiliki pengaruh yang merata untuk wilayah tropis. Komponen utama kedua menunjukkan bahwa fluktuasi tinggi tropopause di lintang 15o - 20o lebih dipengaruhi oleh variasi insolasi musiman. Komponen utama ketiga dipengaruhi oleh fenomena Semi-Annual Oscillation (SAO) yang berkorelasi tinggi di wilayah ekuator. Respon setiap fenomena tertentu memiliki selisih waktu (time lag) terhadap tinggi tropopause.
Keyword: Analisis Komponen Utama, analisis spektral, geopotensial, insolasi musiman, insolasi orbital

Judul: Identifikasi Fluktuasi Ketinggian Tropopause di Kawasan Pasifik Tropis
Abstrak: The 30-years (January 1981 – December 2010) ERA-Interim data issued by ECMWF (Europe Center for Medium Range Weather Forecasting) is used for identifying tropopause height fluctuation in tropical Pacific region. Principle component and spectral analysis is done in order to identify the main pattern of tropopause height fluctuation as generator in the region. The result has shown that the predominant fluctuation trigger is periodical 45-month ENSO. Meanwhile insolation fluctuation due to earth orbital position has placed second with 12- month period after ENSO occurrence. The 20-month oscillation period of QBO (Quasi Biennial Oscillation), periodical 6-month variation of SAO (Semi Annual Oscillation), and 6-month period of MJO (Madden Jullian Oscillation) give weaker influence on tropopause height fluctuation in the region than that of ENSO and insolation. Eigen vector distribution from principle component shows that these five oscillations are very influential and dominant in tropical west Pacific as response of interaction of the five oscillations with Walker circulation in tropical Pacific.
Keyword: Bogor Agricultural University (IPB), Spectral, Walker circulation, Tropopause height fluctuation, Principle component analysis

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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