Judul: Proses Peminyakan (Fatliquoring) pada Penyamakan Kulit Ikan Tuna (Thunnus sp) untuk Bahan Bagian Atas Sepatu
Abstrak: Fatliquoring is part of tanning process, which penetrate the fatliquoring agent into leather’s empty cells. This process can change the physical properties of leather, which make it softer, more elastic, flexible and give smooth grain surface. This research was conducted to observe the influence of fatliquor addition on physical characteristics of tuna’s skin for the shoe upper. Responses measured were thickness, shrinkage temperature, tear strength, tensile strength, elongation at break and organoleptic properties. The types of fatliquor agent used in this study were natural and synthetic, and the dosages were 3%, 6%, 9%, 12% and 15%. Based on this research, the types of fatliquoring agent significantly affected the tear strength and elongation at break. The dosages of fatliquor which was nested in the type of fatliquor agent significantly affected the shrinkage temperature, tear strength, tensile strength, and elongation at break. There was no factor that significantly affected the thickness increase. The best condition in this research was reached by synthetic fatliquoring agent with dosage of 3%. The best condition gave thickness increase of 32.4%, shrinkage temperature of 125oC, tear strength of 95.3 N/mm, tensile strength of 27.9 N/mm2, elongation at break of 45.3%, with a good natural brown colour, smooth of feel/handle and good elasticity.
Keyword: Bogor Agricultural University (IPB), tuna skin, physical properties, fatliquoring agent, fatliquoring

Judul: Penyamakan Kulit Ikan Tuna (Thunnus sp.) Dengan Menggunakan Penyamakan Kombinasi Aldehida dan Nabati
Abstrak: The research of tuna’s leather tanning had been developed at laboratory scale with some type of tannages and not yet achieved optimum results. Therefore, further research is directed toward the combination of several types of tannage in order to obtain the optimum result. Combination tanning is a tanning process using two or more tannages in order to complete each other’s advantage and disadvantage. This research aimed to determine the effects of vegetable tannages (e.g. mimosa, gambier, and quebracho) and its concentrations (10%, 15%, and 20%) on the quality of leather produced using combination tanning. It also aimed to determine the best combination of treatments. Based on the result of this research, the type of vegetable tannages had a significant effect on increase of thickness, shrinkage temperature, tear strength, and elongation at break of the leathers. Concentration had no significant effect on physical properties of tanned leather. Interaction of two factors had no significant effect on physical properties of tanned leather. Combination tanning using 3% glutaraldehyde and 20% mimosa presented the best result. The physical properties of tanned leather resulted were 20.8% increase of thickness, shrinkage temperature of 88°C, tensile strength of 17.8 N/mm2, elongation of break of 41.4%, and tear strength of 54.59 N/mm². Organoleptic properties of the tanned leather were flexibility (fell or handle) in the scale of 6–7 and color of 7–8.
Keyword: tanned leather properties, vegetable tannages, glutaraldehyde, combination tanning, leather

Judul: igenvalues and Eigenvectors of Tridiagonal Matrix with Non Constant and Recurrent Diagonal Entries.
Abstrak: Matriks tridiagonal adalah suatu matriks yang mempunyai entri-entri bernilai nol kecuali pada diagonal utama, di bawah diagonal utama (subdiagonal) dan di atas diagonal utama (superdiagonal). Entri pada diagonal utama tidak konstan dan berulang. Setiap entri pada matriks tridiagonal ini adalah bilangan kompleks. Dalam karya ilmiah ini, akan dibuktikan 3 teorema untuk menentukan nilai eigen dengan 2 kasus dan 1 teorema untuk menentukan vektor eigen. Teorema pertama menentukan polinomial karakteristik dari matriks tridiagonal. Polinomial karakteristik dari matriks tridiagonal tersebut digunakan untuk menentukan nilai eigen pada teorema kedua dan ketiga serta menentukan vektor eigen pada teorema keempat
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