Judul: Hydrogel Formulation Cassava Pulp Waste-Acrylic Acid-Acrylamide Enriched with Urea Fertilizer
Abstrak: Hidrogel dikenal sebagai polimer yang dapat memuat sejumlah banyak air dan pupuk tetapi juga dapat melepaskannya secara perlahan. Hidrogel disintesis menggunakan onggok dicangkok dengan asam akrilat dan akrilamida, diikat silang menggunakan N,N’-metilenbisakrilamida (MBA) dengan variasi konsentrasi 0, 1, dan 2%. Pemuatan pupuk dilakukan menggunakan metode dua langkah dengan variasi konsentrasi 0; 2,5; dan 5%. Hidrogel dengan variasi MBA dan konsentrasi pupuk dianalisis dengan pengujian nilai fraksi gel, swelling, kekerasan, kelengketan, pemuatan, dan pelepasan pupuk. Kapasitas urea yang termuat pada hidrogel dipengaruhi oleh besarnya kemampuan hidrogel dalam menjerap urea. Urea yang termuat akan mempengaruhi persen pelepasan urea. Perlakuan MBA 2% termuat urea 5% menjadi perlakuan terbaik dalam penelitian ini, karena nilai fraksi yang tinggi dan nilai kekerasan yang tidak terlalu tinggi. Sehingga parameter penting hidrogel dalam kekuatan dan biodegradable ini cukup baik. Selain itu, nilai swelling yang tidak terlalu rendah serta memiliki kemampuan pemuatan pupuk yang cukup tinggi dengan pelepasan yang lambat.
Keyword: hydrogel, cross linking agent, urea release, loading urea

Judul: Pemuatan dan Pelepasan Pupuk Urea pada Hidrogel Asam Akrilat-Akrilamida Berbasis Onggok Singkong
Abstrak: Proses pemupukan pada tanaman yang kurang efektif akan menurunkan produktivitas tanaman. Pemuatan pupuk pada hidrogel dapat dijadikan sebagai salah satu solusi untuk mengontrol proses pemupukan yang lebih efektif. Hidrogel disintesis dari onggok dan polimer asam akrilat akrilamida menggunakan metode ikat silang kimia. Selanjutnya, hidrogel dimuati urea dengan variasi konsentrasi 0%, 3%, 5%, 7%, dan 9% menggunakan metode teknik dua langkah. Hasil penelitian menunjukkan bahwa penambahan urea pada proses perendaman hidrogel mampu meningkatkan kemampuan swelling dan kekerasan hidrogel, serta menurunkan nilai kelengketan hidrogel. Selain itu, peningkatan konsentrasi urea juga berpengaruh pada proses pelepasan pupuk. Semakin tinggi konsentrasi urea, semakin rendah persentase pelepasan pupuk yang diperoleh. Proses pelepasan urea pada penelitian ini cenderung terjadi secara cepat pada awal pengukuran dan lepas secara perlahan setelah 24 jam pengukuran., The fertilization process on plants that are less effective will reduce plant productivity. The addition of fertilizer to the hydrogel can be used as a solution to control the fertilization process more effectively. The hydrogel was synthesized from cassava and acrylic acid polymer acrylamide using the chemical crosslinking method. Furthermore, the hydrogel was loaded urea with variations in concentrations of 0%, 3%, 5%, 7%, and 9%. The loading of urea fertilizer on the hydrogel was carried out by a two-step technique. The results showed that the addition of urea in the hydrogel immersion process was able to increase the swelling ability and hydrogel hardness, as well as reduce the hydrogel adhesiveness value. In addition, the increase in urea concentration also affects the process of releasing fertilizer. The higher the concentration of urea fertilizer, the lower the percentage of fertilizer released. The process of releasing urea in this study tends to occur quickly at the beginning of the measurement and slowly after 24 hours of measurement.
Keyword: hydrogel, fertilizer loading, fertilizer release, urea

Judul: Thermal Characteristics and Dynamics of Tropical Cyclone over Western North Pacific Ocean: A Case Study of Typhoon Songda (Chedeng) 2011
Abstrak: The frequent occasion of Tropical Cyclone (TC) over Western North Pacific (WNP) Ocean lies from 10˚N to 26˚N and 121˚E to 170˚E. Sources of TC development come from warm ocean temperature where latent heat is released during condensation processes and subsequently concentrated in the boundary layer. Relative humidity at 850-700 hPa is responsible to produce the most intense storm. Meanwhile, weak vertical wind shear between 850-200 hPa is one of the dynamical factors that lead to the development of TC. Pressure level of 850-200 hPa is chosen to minimize the thermodynamic effect in the lower troposphere. Typhoon Songda (Chedeng in the Philippines) or TSC lasted from May 18th to 30th, 2011 and strengthened into powerful Super Typhoon stage between May 24th and 27th. Long curving track and the exhibition of all sequences of TC life cycle, TSC is then considered as an ideal case of TC. The objective of the study with case of TSC is to investigate the role of thermal characteristics and dynamics on TC intensity. The research is carried out by using Advanced Research of Weather Research and Forecasting model (WRF ARW model) version 3.3. Two domains are employed in the model. The first domain situate from 02˚N to 40˚N and 118˚E to 149˚E and cover spatial resolution () of 33.1 km. The second domain situate from 09˚N to 27˚N and 119˚E to 132˚E with of 11 km. Timestep of the model () is 120 seconds. The model is supported by the following physical parameterization, i.e., Yonsei University Scheme (YSU) in the boundary layer, Kain-Fritsch scheme (KF) in the cumulus, and WRF Single-Moment 3-class scheme in the microphysics. Initial meteorological condition prior to the formation of the cyclone is generated using WRF ARW standard-release model. Sensitivity of the model output is obtained from a selected single-parameter change scenarios, namely, 10 % to 20 % decrease and increase of wind shear initial data at 850-200 hPa, and by 10 % to 20 % decrease of relative humidity initial data at 850-700 hPa. The result showed that the negative correlations between wind shear and intensity are found in wind shear scenarios. Wind shears of 10 ms-1 which lead to strengthening of the wind intensity in the early period of Typhoon development are found in wind shear scenarios. The effect of wind shear changes on wind intensity is statistically significant in the 20 % wind shear scenarios. During mature stage, weak wind intensity occurred when wind shear increase as given in the WRF standard-release and the 20 % decreasing scenario. Different situation is found in the 20 % increasing scenario where wind shear tend to weak and lead to strong wind intensity at this stage. Meanwhile, the reduction of moisture supply at 850-700 hPa resulting from 20 % decreasing relative humidity play a major role in the weakening of wind intensity and reduces mechanical energy of the cycle process as much as 300 J kg-1.
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