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: 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: A Continuous Vaccination Strategy in the SVIR Epidemic Model
Abstrak: Vaccination is conducted to minimize the spread of a disease. The vaccination is usually done several times within a fixed time interval. In the SVIR model, it is assumed that individuals do not get immediate immunity following a vaccination program. So according to process of vaccination on SVIR model, there are two strategies, i.e. the continuous vaccination strategy (CVS) and the pulse vaccination strategy (PVS). In this study, only the CVS strategy in epidemic model SVIR is considered. Results of the study indicate that dynamics of the CVS system depends on the basic reproductive number. If the basic reproductive number is less than one, then the disease-free fixed point is asymptotically stable. It means that the disease will eventually disappear from the population. Conversely, if the basic reproductive number is greater than one, then the endemic fixed point is asymptotically stable, which means that the disease will remain exist in the population. Simulation result shows that the vaccination would minimize the spread of disease by reducing the basic reproductive number. If the time for the vaccinated recipients to obtain the immunity, as well as a possibility of vaccinated recipients to be infected are neglected, then the disease will be eradicated. This condition is called an over-evaluating effect of vaccination.
Keyword: