Judul: Pengujian Pelepasan Hidrogel Karagenan sebagai Pembawa Pupuk pada Tanah
Abstrak: Hidrogel adalah polimer hidrofilik yang mampu memuat air berkali lipat dari bobot aslinya. Hidrogel disintesis menggunakan karagenan, asam akrilat dan akrilamida, diikat silang dengan 1% N,N’-metilenbisakrilamida (MBA), serta 16% amonium pesulfat (APS). Hidrogel diuji dan dianalisis nilai swelling, kinetika swelling, fraksi gel, kapasitas adsorpsi, pemuatan pupuk, pelepasan pupuk, analisis gugus fungsi, serta morfologi permukaan hidrogel. Nilai swelling pada hidrogel dengan variasi pupuk urea 0%, 5% dan 10% dipengaruhi oleh kapasitas adsorpsi dan konstentrasi urea sehingga variasi urea 5% memiliki nilai swelling terbaik dan mampu memuat pupuk sebanyak 2273,5 mg/L (54,507%). Pelepasan pupuk urea 5% dan 10% diuji pada tanah pasirdan tanah andosol dipengaruhi oleh nilai swelling dan variasi tanah. Hidrogel pupuk 10% pada tanah pasir merupakan pelepasan pupuk paling lambat. Hidrogel pupuk 5% dan 10% termasuk ke dalam pupuk lepas lambat. Pelepasan pupuk yang lambat memiliki pori hidrogel yang kecil, serta memiliki nilai swelling dan kapasitas adsorpsi tidak terlalu tinggi., Hydrogel is a hydrophilic polymer that can contain water many times its original weight. The hydrogel was synthesized using carrageenan, acrylic acid and acrylamide, cross-linked with 1% N,N’-methylenebisacrylamide (MBA), and 16% ammonium pesulfate (APS). The hydrogel was tested and analyzed for swelling value, swelling kinetics, gel fraction, adsorption capacity, fertilizer loading, fertilizer release, functional group analysis, and hydrogel surface morphology. The swelling value of the hydrogel with variations of 0%, 5% and 10% urea fertilizer is influenced by the adsorption capacity and urea concentration so that the 5% urea variation has the best swelling value and is able to contain fertilizer as much as 2273.5 mg/L (54.507%). The release of 5% and 10% urea fertilizer tested on sandy soil and Andosol soil was influenced by swelling values and soil variations. 10% fertilizer hydrogel in sandy soil is the slowest release of fertilizer. 5% and 10% fertilizer hydrogels are included in slow release fertilizers. Slow releasing fertilizer has small hydrogel pores, and has a swelling value and not too high adsorption capacity.
Keyword: carrageenan, fertilizer release, hydrogel, soil

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: Penentuan Nilai Eigen dan Vektor Eigen dari Matriks Tridiagonal 2-Toeplitz dengan Pendekatan Polinomial Chebyshev
Abstrak: The eigenvalues and eigenvectors of a matrix can be determined by finding its characteristic polynomials. The characteristic polynomials of a tridiagonal 2-Toeplitz matrix is shown to be closely connected to polynomials which satisfy the Chebyshev recurrence relationship. If the order of the matrix is odd, then the eigenvalues are found explicitly in terms of the Chebyshev zeros and the eigenvectors are found in terms of the polynomials satisfying the recurrence relationship. For even ordered matrices, the situation is more complicated. The problem in these cases is that although the Chebyshev recurrence formula is still applied, its initial values are not generating Chebyshev polynomials
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