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: 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: 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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