Judul: Superabsorben Polimer sebagai Agen Pembawa Pupuk Urea: Studi Pelepasan Pupuk Terkendali
Abstrak: Setengah dari urea pada proses pemupukan tidak digunakan oleh tanaman. Namun hilang ke ekosistem melalui limpasan dan penguapan. Superabsorben Polimer (hidrogel) mampu menyerap air sebanyak ribuan kali berat awalnya sehingga dapat digunakan untuk proses pemupukan. Hidrogel yang dimuatkan pupuk sebagai pembawa pupuk dapat melepaskan pupuk secara terkendali. Hidrogel dapat disintesis dari bahan alami dan sintetis. Pencangkokan kopolimerisasi pada hidrogel dengan ikat silang kimia menggunakan agen penaut silang N,N-metilen-bis-akrilamida. Perbedaan perlakuan konsentrasi MBA memengaruhi kapasitas hidrogel dalam proses pemuatan urea serta banyaknya urea yang terlepas pada proses pelepasan. Dengan penambahan konsentrasi MBA jumlah urea termuat cenderung naik namun urea yang terlepas makin menurun. Hidrogel berbasis Onggok:AA-Aam terbaik pada penelitian ini adalah hidrogel dengan penambahan konsentrasi MBA 1,5 % karena memiliki nilai swelling yang tidak terlalu rendah, sifat mekanik yang kuat, fraksi gel yang lebih tinggi, pemuatan yang tidak terlalu kecil serta pelepasan yang lebih stabil dan optimum. Sedangkan tanaman yang baik untuk penggunaan hidrogel adalah tanaman hortikultura seperti tanaman cabai, tomat dll., Half of the urea in the fertilizing process is not used by plants. But it is lost to the ecosystem through runoff and evaporation. Polymer Superabsorbent (hydrogel) is able to absorb water as much as thousands of times its initial weight so that it can be used for the fertilization process. Hydrogels loaded with fertilizer as fertilizer carriers can release fertilizer in a controlled manner. Hydrogel can be synthesized from both natural and synthetic materials. Copolymerizing grafting on hydrogels with chemical crosslinking using N,N-methylene-bis-acrylamide crosslinking agents. The difference in MBA concentration treatment affects the hydrogel capacity in the urea loading process as well as the amount of urea released in the discharge process. With the addition of the MBA concentration, the amount of urea contained tends to increase but the urea released decreases. The best Onggok-based hydrogel: AA-Aam in this study is a hydrogel with an additional MBA concentration of 1.5 % because it tends to have a not too low swelling value, strong mechanical properties, higher gel fractions, not too small loading and a more stable and optimum discharge. While the plants that are good for the use of hydrogel are horticultural crops such as chili plants, tomatoes etc.
Keyword: cross linking agent, hydrogel, onggok, urea release

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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