Judul: Penentuan konsentrasi Krom dan Gambir pada penyamakan kulit Ikan Tuna (Thunnus albacore)
Abstrak: Penyamakan dengan krom merupakan salah satu jenis penyamakan yang paling banyak digunakan oleh seluruh industri kulit di dunia karena kelebihannya dalam penyamakan kulit, seperti memiliki stabilitas hidrotermal yang tinggi dan sifat fisik yang baik. Namun, kerugian yang ditimbulkan juga telah menarik perhatian industri kulit yang ada di dunia karena penyamakan krom menghasilkan limbah yang sifatnya beracun. Oleh karena itu, penyamakan kombinasi dilakukan untuk mengurangi pemakaian krom. Penyamakan kombinasi menggunakan krom dan nabati akan menghasilkan kulit dengan sifat fisik yang lebih baik dan limbah krom yang lebih sedikit. Penelitian ini bertujuan untuk mengetahui pengaruh konsentrasi bahan penyamak krom dan gambir terhadap sifat fisik dan organoleptik pada penyamakan kombinasi kulit ikan tuna dan menentukan kombinasi konsentrasi terbaik antara kedua bahan penyamak, serta menentukan sifat-sifat kulit tuna yang dihasilkan. Bahan penyamak yang digunakan berupa krom dengan konsentrasi 1%, 3%, 5%, 7% dan gambir sebesar 20% dan 30%. Parameter yang diamati adalah peningkatan tebal, suhu kerut, kuat sobek, kuat tarik, perpanjangan putus, dan sifat organoleptik kulit. Hasil penelitian menunjukkan bahwa konsentrasi krom berpengaruh signifikan terhadap semua parameter sifat fisik, konsentrasi gambir berpengaruh signifikan terhadap semua parameter sifat fisik kecuali suhu kerut. Interaksi antara konsentrasi krom dan gambir juga terlihat pada beberapa parameter, seperti peningkatan tebal, kuat tarik, dan perpanjangan putus. Kombinasi terbaik dihasilkan oleh kulit dengan konsentrasi gambir 20% dan krom 5%. Peningkatan tebal yang dihasilkan sebesar 31.2%, kuat sobek 141.6 kg/cm, kuat tarik 163.6 kg/cm2, dan perpanjangan putus 38.9%. Uji organoleptik menunjukkan warna kulit samak cenderung lebih cerah, feel/handle yang lebih baik, dan tingkat kelemasan yang baik, sehingga kulit dapat digunakan untuk produk seperti ikat pinggang., Chrome tanning is one type of tanning that is most widely used by all leather manufacture in the world because of its excellence on leather tanning, like high hydrothermal stability, good physical properties, and so on. However, the loss that was showed has become worldwide concern because chrome tanning produced toxic waste. Therefore, combination tanning was used to reduce usage of chrome. Combination tanning using chrome and vegetable tanner will produce better physical properties leather and less chrome waste. The objectives of this study were to determine the effect of chrome amount and gambir amount on physical and organoleptic properties in the combination tanning of tuna skin tannage and to decide the best amount combination of the two tannage, also to determine the properties of the tuna leather. The used tannages were chrome with amounts of 1%, 3%, 5%, 7%, and gambir with amounts of 20% and 30%. The observed parameters increased in thickness, shrinkage temperature, tear strength, tensile strength, elongation at break, and organoleptic properties. The results show that chrome amount has significant effect to all physical properties parameters, gambir amount has significant effect to all physical properties parameters except shrinkage temperature. Interaction between chrome and gambir amount was also showed on some parameters, like thickness, tensile strength, and elongation at break. According to this study, the best combination was showed by the leather with 20% of gambir and 5% of chrome. Increased thickness that was showed was 31.2%, tear strength was 141.6 kg/cm, tensile strength was 163.2
Keyword: penyamakan kombinasi, konsentrasi krom, konsentrasi gambir

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: 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.
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