Judul: Penentuan Konsentrasi Ca(OH)2 dan Suhu untuk Proses Pengapuran (Liming) Kulit Ikan Tuna
Abstrak: Liming is one of the most important processes in beamhouse and has many functions relating to the nature and quality of leather. Concentration of calcium hydroxide and temperature are thought to be a factor affecting the liming process and the quality of leather produced. The objectives of this study were to determine the characteristics of tuna skin, to determine the effect of the concentration of calcium hydroxide and temperature on the liming, and to determine the best treatment of the concentration of calcium hydroxide and temperature on the quality of limed pelt. There were four responses observed, i.e. the protein content, fat content, swelling, and pH. Based on this research, tuna skin had higher level of protein that was high enough to be processed into leather. Treatment of calcium hydroxide concentration did not significantly effect to all responses. Level of 5% calcium hydroxide concentration was the best treatment, as it gave three responses that achieve the best conditions. Temperature treatment showed a significant effect on the responses of fat content and swelling. Specified temperature as the best level was 30 °C, because there were two responses that achieve the best conditions at that level.
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Judul: Penyamakan Kulit Ikan Tuna (Thunnus sp.) dengan Kombinasi Penyamak Krom dan Nabati
Abstrak: Tanning is a way to change unstable rawhide (easily damaged by physical, chemical and biological effects) into a stable leather against those effects. Combination tanning method was a tanning process using two or more tannages in order to complete each other advantages and disadvantages to obtain leather with desired characteristics. Tanning using chrome would increase the flexibility, resistency of high temperature and tensile strength of leather. While vegetable tannage used in tanning gave an effect on physical quality on leather, including tensile strength, tear strength and other characteristics. The main purpose of this study were determined the effect of type and concentration of vegetable tannage on physical and organoleptic characteristics of skin tannage in the tanning process, to decide the best type and concentration of tannage for tanning, and to decide the characteristic of the leather. Tannages used were chrome with a concentration of 8% and vegetable tannages (mimosa, gambier, quebracho) with concentrations of 10%, 15% and 20%. The observed reponses in this study were thickness, shrinkage temperature, tensile strength, tear strength, elongation at break, and organoleptic characteristics. Based on the study, gambier with 20% concentration combined with 8% chrome produced the best quality of leather, highest increase thickness, tear strength of 84.76 N/mm, tensile strength of 22.68 N/mm2 and elongation at break of 57.38%. Organoleptic test showed that the colours produced by gambier looked more attractive, natural, finer texture, so that can be applied for material in sofa or jacket manufacture.
Keyword: vegetable, chrome, combination tanning, tuna’s skin

Judul: Metrik Einstein (Anti-) Self-Dual Berdimensi Empat dengan Metode Cartan
Abstrak: Gravitational field equation can be formulated in differential forms (differential geometry), which describes gravity as a manifestation of the curvature of space-time. Curvature of space-time is characterized by a metric that satisfies the gravitational field equation. With differential forms it can be formulated the (anti-) self-dual Einstein equation, which is a modification of the Cartan structure in (anti-) self-dual basis. Calculation of (anti-) self-dual metric with (anti-) self-dual Einstein equation is simpler than the calculation using Christoffel symbols.
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