Judul: Slow release urea by coating with Poly(acrylamide), Poly(acrylic acid), and paraffin
Abstrak: The use of conventional urea is less efficient, about 20 to 70% urea fertilizer is lost to the environment. Coating urea fertilizer is one way to controlling slowrelease urea to the environment. A common coating material used is polymer. One method of coating is carried out simultaneously with the process of radical polymerization in the reactor so that the polymer is formed directly deposited on the surface as a fertilizer coating layer. The polymerization takes in an uncontrolled manner, as well as the deposition of polymer on the surface needs to be controlled to form perfect coating. This research aimed to create slow-release urea fertilizers by using a double coating of hydrophilic polymer and paraffin in the designed controlled system. The release pattern and kinetics of slow-release urea fertilizers were determined through the exponential model approach and sigmoidal models. Hydrophilic polymers used were poly(acrylamide) crosslinked with N,N'-methylene-bis-acrylamide (PAM-MBA) and poly(acrylic acid) crosslinked with N,N'-methylene-bis-acrylamide (PAM-MBA). Coating urea granules are designed in a controlled system reactor. The process of reaction carried out at a temperature of 61 °C in three phase of supplying reagent until one hour through the control of an integrated electronics system of microcontroller. Transparent empty sheaths which formed after the soaking of treated granular urea showed the coating on urea granules had been occurred. Characterization of coating material by infrared spectroscopy resulted spectra profiles showed a polymerization and crosslinking had been occurred to form a coating deposit. SEM imaging showed the morphology of coating layer looked like a fiber or needle arrangement which supporting each other, in addition SEM resulted also showed a coating layer thickness of coated urea granule urea coated with PAM-MBA and paraffin was 243 μm, whereas urea coated with PAA-MBA and paraffin MBA and paraffin was 143 μm. The rate of release of urea in water of the uncoated urea, urea coated with paraffin, urea coated with PAM-MBA and paraffin, and urea coated with PAM-MBA and paraffin, respectively were 234.25 ppm/min, 23.84 ppm/min, 38.63 ppm/min, and 21.04 ppm/min. The release pattern of coated urea fertilizer in the soil showed a sigmoidal pattern. The urea coated with PAM-MBA and paraffin showed a match with two sigmoidal models, namely the Richards and Gompertz relation with a correlation coefficient are 0.999. Similarly, the urea coated with PAA-MBA and paraffin showed a match with two sigmoidal models, namely the Morgan-Mercer-Flodin (MMF) and Logistic with each correlation coefficient are 0.999 and 0.986. The fitting curve showed that the double coating with polymer and paraffin can provide release urea with good sigmoidal pattern, unlike urea coated with paraffin alone showed a match with Logistic models only, whereas urea without coating could not be approximated by sigmoidal models.
Keyword: coating, fertilizer release, polymer, sigmoidal pattern, urea

Judul: Pelapisan Pupuk NPK dengan Poli(Asam Akrilat) Tertaut-Silang-N,N’-Metilena-bis-akrilamida dan Berbagai Konsentrasi Parafin
Abstrak: Coating of NPK fertilizer can increase the efficiency of fertilizing, fertilizer’s loss is reduced and environmental pollution is minimized. N,N’-Methylene-bis-acrylamide-crosslinked poly(acrylic acid) (MBA-PAA) and paraffin can be used as fertilizer coating. MBA-PAA layer was made from acrylic acid as monomer, benzoyl peroxide as initiator, N,N'-methylene-bis-acrylamide as cross linker, and chloroform as the polymerization medium. The second layer, paraffin was varied with the concentrations of 5%, 10%, and 15%. Release in static water media and leaching test in soil media were carried out. The results showed sigmoid patterns for urea release as well as leaching. Release and leaching test of NPK coated with MBA-PAA and paraffin 15% showed the slowest urea release curve. Urea release rate was determined by a mathematical approach y = ɑ(1 e (–bx)). The slowest rate of urea release and leaching were 0.21 and 0.32% per minute, respectively. The NPK fertilizer can be categorized as slow release fertilizer, but it cannot be regarded as controlled or measured release fertilizer yet
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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