Judul: Sintesis Hidrogel Berbasis Karagenan pada Aplikasi Pemupukan: Variasi Konsentrasi Metilenbisakrilamida.
Abstrak: Hidrogel adalah jaringan polimer tiga dimensi pada polimer hidrofilik dengan ikatan silang yang mempunyai kemampuan menyerap air. Karagenan sebagai polimer alami dipilih karena dapat berikatan dengan asam akrilat dan membentuk gel yang baik dan elastis. Hidrogel disintesis menggunakan larutan karagenan dengan asam akrilat dan diikat silang menggunakan MBA dengan variasi konsentrasi sebesar 0,5 dan 1%. Pengujian hidrogel menganalisis nilai swelling, fraksi gel, kelengketan, kekerasan, pemuatan dan pelepasan pupuk. Kekuatan hidrogel dipengaruhi oleh MBA, perlakuan MBA 1% tanpa termuat urea menjadi perlakuan terbaik dalam penelitian ini karena memiliki nilai kekerasan yang tidak terlalu tinggi dan nilai fraksi gel yang tinggi. Dari hasil yang didapat, hidrogel berbasis karagenan belum mampu diaplikasikan sebagai pupuk lepas lambat karena tingkat pelepasan mencapai 21% pada satu jam pertama pengukuran. Memiliki nilai swelling yang tidak rendah dengan kemampuan pemuatan pupuk cukup tinggi dan signifikan dalam menahan pelepasan pupuk menjadi parameter yang penting dalam hidrogel., Hydrogels are three-dimensional polymer networks on hydrophilic polymers with cross-links that have the ability to absorb water. Carrageenan as a natural polymer was chosen because it can bind with acrylic acid and form a good and elastic gel. Hydrogels were synthesized using a solution of carrageenan with acrylic acid and crosslinked using MBA with varying concentrations of 0.5 and 1%. Hydrogel testing analyzed the value of swelling, gel fraction, stickiness, hardness, loading and releasing of fertilizers. Fertilizer loading was carried out using a urea solution of 0 and 5% concentration. Hydrogel strength was affected by MBA, 1% MBA treatment without urea loading was the best treatment in this study because it had a hardness value that was not too high and a high gel fraction value. From the results obtained, carrageenan-based hydrogel could not be applied as a slow release fertilizer because the release rate reached 21% in the first hour of measurement. Having a swelling value that is not low with sufficiently high and significant fertilizer loading ability to restrain fertilizer release is an important parameter in hydrogels.
Keyword: Crosslinking agent, hydrogel, carrageenan, urea release

Judul: Pengaruh Konsentrasi Urea Terhadap Karakteristik Hidrogel Asam Akrilat-Akrilamida Berbasis Karagenan.
Abstrak: Dalam rangka meningkatkan efisiensi pemupukan, telah dilakukan sintesis hidrogel dengan metode ikat silang kimia dan variasi konsentrasi pupuk urea 0, 5, dan 10 %. Bahan dasar yang digunakan adalah asam akrilat, akrilamida, dan karagenan. Pengujian yang dilakukan meliputi uji sewlling, fraksi gel, kinetika swelling, uji mekanik, pemuatan dan pelepasan pupuk. Hasil penelitian menunjukkan hidrogel paling optimum untuk media pelepasan pupuk adalah hidrogel dengan konsentrasi urea 5 %, pada konsentrasi tersebut hidrogel mencapai swelling paling tinggi yaitu sebesar 26168,5 %, sifat mekanik juga paling kuat pada konsentrasi 5 % dimana nilai hardness sebesar 1,36 N. Selain itu, pelepasan pupuk urea pada konsentrasi 5% juga lebih lambat dibandingkan 10%, Pelepasan pupuk pada hidrogel dengan konsentrasi urea 5 % berkisar antara 16 % sampai 18 % selama 4 hari pengukuran, akan tetapi kedua perlakuan konsentrasi 5 % dan 10 % memiliki kecenderungan pelepasan yang sama, dimana pelepasan cenderung cepat pada 5 jam pertama dan mulai stabil pada pengukuran 24 jam. Oleh karena itu, berdasarkan beberapa respon pengujian dapat disimpulkan bahwa perlakuan konsentrasi urea 5 % lebih optimal untuk hidrogel sebagai media pelepasan pupuk terkendali., In order to increase fertilization efficiency, hidrogel synthesis has been carried out by chemical crosslinking method and variations in urea fertilizer concentrations of 0, 5, and 10%. The basic ingredients used are acrylic acid, acrylamide, and carrageenan. Tests carried out include sewlling tests, gel fractions, swelling kinetics, mechanical tests, fertilizer loading and release. The results showed that the most optimal hydrogel for fertilizer release media was a hydrogel with a urea concentration of 5%, at that concentration the hydrogel reached the highest swelling of 26168.5%, mechanical properties were also the strongest at a concentration of 5% where the hardness value was 1.36 N. In addition, the release of urea fertilizer at a concentration of 5% was also slower than 10%, the release of fertilizer on hidrogel with a urea concentration of 5% ranged from 16% to 18% for 4 The day of measurement, however, both 5% and 10% concentration treatments have the same tendency to release, where release tends to be rapid in the first 5 hours and stabilizes at 24 hours. Therefore, based on several test responses, it can be concluded that a urea concentration treatment of 5% is more optimal for hydrogel as a controlled fertilizer release medium.
Keyword: hidrogel, karagenan, pupuk urea, carrageenan, chemical, hydrogel, urea fertilizer

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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