Judul: Formulasi Pupuk Nitrogen Lambat Tersedia dari Bahan Urea, Zeolit, dan Asam Humat serta Pengaruhnya terhadap Pertumbuhan Jagung
Abstrak: The quality of agricultural land in Indonesia was declining progressively and it affect to the decrease of crop production. It is well known that N fertilizer is inefficient due to evaporation into atmosphere and leached into the grown water. The objectives of this research were to study the formulation of slow release N-fertilizer made from urea, zeolite, humic acid, and polymer; to study the pattern of nitrogen release from this modified slow release fertilizer; and to evaluate the effect of modified slow release fertilizer on corn growth. The ratio of urea and zeolite used in this experiment was prepared with the ratio of urea (U) and zeolite (Z) 7:3 and 8: 2, humic acid (HA) of 2 and 2.5% and arabic gum as the binding material. The modified fertilizers were put into the percolation column. The volume and concentration of ammonium-N and nitrate-N were collected and measured during one month percolation with Kjeldahl methode. The modified fertilizers then used to evaluate the effect of the fertilizers on growth of corn in greenhouse experiment. The results showed that the composition of the six N fertilizer were prepared by coating with zeolite, humic substance, and gum arabic characterized as a slow release fertilizer. Zeolite, humic substance, and gum arabic or combinations there of as coating agent is able to reduce the peak release of N-NH4+ and N-NO3- and change the pattern of release to be still available until the end of the test period. Based on the data of corn’s growth, slow release fertilizer forms obtained did not match the corn crop N requirement in accordance with the physiological growth so that the best growth is obtained only by urea which has a high solubility. Humic substance influential in terms of the physiological properties of corn compared to its role as an encapsulation on slow release fertilizer.
Keyword: ammonium-N, humic acid, nitrate-N, slow release fertilizer, zeolite

Judul: Studi "Slow Release Fertilizer" (SRF): Uji efisiensi formula pupuk ersedia lambat campuran urea dengan zeolit
Abstrak: Nitrogen (N) is one of macro plant nutrients which very important for plant growth. However, this nutrient is easily loss from soil because of leaching, change to other forms, and volatilizing to the air. Therefore, efforts to increase the efficiency of nitrogen fertilizer for improvement of agricultural production is necessary. Many attempts were done to reduce loss of nitrogen from soil, such as making N fertilizer as slow release form (SRF). However, most of slow release fertilizer use chemical materials as bider which can making bad effect for soil. Searching other materials which more cordial to environment is need. Zeolite is an unique mineral having high cation exchange capacity (120-180 meI100g) and porous structure may be used for slow release agent of nitrogen fertilizer. With the high exchange of ammonium ion, zeolite can adsorb and save temporary of nitrogen and release into the soil when needed. The objective of this research was to know the efficiency of slow release fertilizer made from mixture of urea and zeolite, with compared to urea fertilizer that ordinary used by farmers (urea prill and urea granule). The experiment was carried out by randomized complete design with 17 treatments and 3 replications. This experiment used paddy of Ciherang variety. Paddy was planted into pot having diameter of 28 cm and high of 32 cm. The growth parameters of paddy plant and production were recorded and evaluated. The results showed that slow release fertilizer which made by mixture of urea and zeolite at the accurate composition, binder and application can proceed production higher than urea prill and urea granule. Slow release fertilizer with ratio of urea and zeolite of 50:50 has the efficient value higher than that of slow release fertilizer with ratio of urea and zeolite of 70:30. That conclusion is shown from the paddy production. Aplication of SRF (50:50) containing 70% N gave the same production of normal dose. Therefore, slow release fertilizer with ratio of urea and zeolite of 50:50 increased the efficiency of urea 30%.
Keyword: 

Judul: Invers dari Matriks Tridiagonal Jacobi
Abstrak: Suatu matriks berukuran n×n dinamakan matriks tridiagonal jika untuk . Karya ilmiah ini memberikan algoritma yang mudah untuk menemukan invers ( dari matriks tridiagonal Jacobi yang simetrik dan nonsimetrik. Setiap elemen pada matriks tridiagonal ini adalah bilangan real. Terdapat 3 lema dan 2 teorema untuk menentukan . Lema pertama menunjukkan persamaan utama dalam membuktikan lema-lema dan teorema-teorema selanjutnya. Invers dari matriks yang simetrik dibuktikan oleh lema kedua yang menunjukkan elemen-elemen baris ke- dari . Selanjutnya, lema kedua dilengkapi dengan teorema pertama yang menunjukkan elemen-elemen dengan . Invers dari matriks yang nonsimetrik dibuktikan oleh lema ketiga yang menunjukkan elemen-elemen dengan dan elemen-elemen dengan dibuktikankan oleh teorema kedua.
Keyword: symmetric, nonsymmetric, matrix