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: The Effectiveness of Oil as a Slow Release Urea Nitrate Coating Material on Fermentability, Digestibility and In Vitro Gas Production
Abstrak: Penelitian ini bertujuan untuk mengevaluasi efektivitas minyak sebagai coating slow release urea nitrat secara in vitro. Penelitian ini menggunakan rancangan acak kelompok (RAK) dengan 5 perlakuan dan 4 kelompok. Perlakuan terdiri dari P0 = ransum kontrol; P1 = P0 + urea; P2 = P0 + urea nitrat; P3 = P0 + urea nitrat dengan coating minyak sawit; P4 = P0 + urea nitrat coating minyak ikan. Parameter yang diamati yaitu pH, konsentrasi ammonia (NH3), volatile fatty acid (VFA), sintesis protein mikroba (SPM), koefisien cerna bahan kering (KCBK), koefisien cerna bahan organik (KCBO), produksi gas, dan gas metan. Analisis data menggunakan sidik ragam dengan perlakuan berbeda nyata dilakukan uji lanjut menggunakan uji Duncan menggunakan software SPSS versi 25. Hasil penelitian menunjukkan bahwa penggunaan slow release urea nitrat dengan coating minyak ikan dan minyak sawit tidak berpengaruh nyata (P>0,05) terhadap pH, NH3, SPM, VFA, KCBK, KCBO, total produksi gas, dan gas metan. Penggunaan SRUN dengan bahan coating minyak sawit dan minyak ikan belum efektif memengaruhi fermentabilitas, kecernaan dan produksi gas in vitro., This study aimed to evaluate the effectiveness of oil as a slow release urea nitrate coating in vitro. This study used a randomized block design (RBD) with 5 treatments and 4 groups. The treatment consisted of P0 = control ration; P1 = P0 + urea; P2 = P0 + urea nitrate; P3 = P0 + urea nitrate with palm oil coating; P4 = P0 + urea nitrate coating of fish oil. Parameters observed were pH, concentration of ammonia (NH3), volatile fatty acids (VFA), microbial protein synthesis (SPM), dry matter digestibility coefficient (KCBK), organic matter digestibility coefficient (KCBO), gas production, and methane gas. Data analysis using analysis of variance (ANOVA) and significantly different treatments were tested with the Tukey's test using SPSS software version 25. The results showed that the use of slow release urea nitrate with fish oil and palm oil coatings had no significant effect (P>0.05) on pH, NH3, SPM, VFA, KCBK, KCBO, amount of gas production and methane gas. The use of SRUN with palm oil and fish oil coatings has not effectively influenced in vitro fermentability, digestibility, and gas production.
Keyword: Coating, urea nitrate, in vitro, oil, slow release

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