Judul: Analisis Penjalaran Gelombang Kelvin di Atas Kototabang Berbasis Data EAR (Equatorial Atmosphere Radar)
Abstrak: Indonesian geographical condition, maritime continent, contribute significant effects in atmosphere dynamics both macro and micro scale. One of equatorial atmospheric waves which play an important role is the Kelvin wave. It was suspected as the trigger of the Intraseasonal Variability phenomenon especially MJO (Madden Julian Oscillation). Studies on propagation and vertical structure of Kelvin wave were still limited on OLR data, GPS, RO, NCEP / NCAR reanalysis and radiosonde. EAR data were expected to explain about propagation and vertical structure of Kelvin wave better. To analyze the Kelvin wave propagation above Kototabang, spectral analysis method were used with both the FFT (Fast Fourier Transform) and the Wavelet technique. Statistical analysis was also done with cross-correlation technique (Cross Corelation Function) and cross Spectral (Cross Spectrum) to see the relevance between Kelvin wave and the KTTL (Kototabang Tropical Tropopause Layer). Based on EAR data over period of 1 December 2007 – 31 December 2008, Kelvin wave was detected above Kototabang with eastward zonal propagation and downwards vertically. Spectral analysis during this period showed that the Kelvin wave appeared periodic every 18 days at 17.41 km altitude near the Tropopause layer (~17 km). Power spectrum analysis indicate that the Kelvin wave energy was stronger during wet season than during dry season. During wet months, the Kelvin wave is dominant at 16.97 km in altitude and appear periodic every 15 days. While in dry months, it is more dominant at 16.52 km in altitude and appeared every 18 days. Statistical analysis results during wet and dry season indicate a correlation between zonal wind dynamics with the fluctuation of Tropopause height, spontaneously and inspontaneously. Cross-spectrum analysis showed that zonal wind dynamics activity affected the height fluctuation of the Tropopause where the Kelvin wave tend to rise the KTTL height during wet season, while in dry season it will lower the KTTL height. Keywords : Kelvin waves, Propagation, EAR, KTTL, Spectral analysis.
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Judul: Analysis of the Vertical Structure of Equatorial  Kelvin Waves in the Upper-Troposphere and Lower-Stratosphere Based on GPS  RO Data
Abstrak: Gelombang kelvin merupakan salah-satu gelombang atmosfer paling dominan di lapisan troposfer-atas dan stratosfer-bawah. Penelitian ini bertujuan untuk menganalisis karakteristik gelombang kelvin dalam struktur vertikal pada lapisan troposfer-atas dan stratosfer-bawah menggunakan data GPS RO. Metode STSA digunakan untuk menganalisis aktivitas gelombang kelvin tiap lapisan dan musiman. Gelombang kelvin dalam struktur vertikal menunjukan arah propagasi miring ke arah timur terhadap ketinggian dan merambat ke bawah terhadap waktu. Karakteristik gelombang kelvin pada lapisan troposfer-atas dan stratosfer-bawah berbeda. Pada lapisan troposfer-atas, gelombang kelvin dominan dipengaruhi oleh aktivitas konvektif yang memperlambat perambatan gelombang sehingga laju fasanya lebih rendah dibandingkan pada stratosfer-bawah. Panjang gelombang vertikal yang ditemukan berkisar pada 2.8-4.9 km pada troposfer-atas, 2.8-7 km pada tropopause, dan 4.9-12.1 km pada stratosfer-bawah. Periode gelombang kelvin yang teramati berkisar antara 4-17 hari dengan bilangan gelombang 1 hingga 4.Analisis musiman pada lapisan troposfer-atas, tropopause, dan stratosfer-bawah menunjukan bahwa gelombang kelvin kuat pada musim JJA dan SON., Kelvin waves are one of the most dominant atmospheric waves in the upper troposphere and lower-stratosphere layers. This study aims to analyze kelvin waves in vertical structures in the upper-troposphere and lower-stratosphere using GPS RO data. STSA method is used to analyze the kelvin wave activity of each layer and its seasonality. Kelvin waves in a vertical structure revealed of propagation tilted eastward for the altitude and propagates downward with time. The characteristics of kelvin waves in the upper-troposphere and lower-stratosphere are different. In the upper-troposphere, kelvin waves are dominantly influenced by convective activity which slows the wave propagation so that the phase speed is lower than in the lower-stratosphere. The vertical wavelengths are 2.8-4.9 km in the upper-troposphere, 2.8-7 km in the tropopause, and 4.9-12.1 km in the lower stratosphere. The kelvin wave period observed ranged from 4-17 days with wave numbers 1 to 4. Seasonal analysis of the upper-troposphere, tropopause, and lower stratosphere shows that the kelvin wave is strong in the JJA and SON seasons.
Keyword: GPS RO, kelvin wave, lower-stratosphere, upper-troposphere

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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