Judul: Pengaruh faktor fisikokimia terhadap pembentukan pigmen oleh bakteri laut Mesophilobacter sp.
Abstrak: It has been conducted an observations on the effect of environmental factors especially physicochemical factors on the growth and pigment formation by a marine bacteria Mesophilobacter sp. The objectives of this research were to study the effect of : 1) cultivation temperature (25oC, 30oC and 35oC); 2) pH of growth medium (5, 7, and 9); 3) salinity of growth medium (0 ppt, 10 ppt, 20 ppt, 30 ppt and 40 ppt), 4) carbon sources (glucose, acetate, citrate, and maltose), and 5) nitrogen sources (peptone, yeast extract, sodium nitrate, and ammonium sulfate) on the growth of bacteria and the pigment formation. Bacteria were cultivated in 500 ml flasks with a working volume of 250 ml in marine broth and incubated on a shaker incubator with the agitation speed of 120 rpm for seven days. Variables that were observed during the cultivation process involved bacterial growth (cell concentration), pigment concentration, and pH. Observations were carried out up to 168 hours. The cell and pigment concentrations were monitored spectrophotometrically. The results indicated that Mesophilobacter sp. grew well and formed the highest concentration of pigment (P) at temperature 30oC, with value of P 0.12 + 0.003 (λ 463 nm). At pH experiment the highest average P was obtained from medium with pH 9 was 0.14 + 0.006 (λ 463 nm) and significantly different from pH 7 (p <0.5). At salinity experiment, the highest average P obtained from the growth medium with 10 ppt salinity is 3.54 + 0.11 in λ 368 nm. At carbon source experiment, the highest average of P were obtained from maltose, with value 12.13 + 1.33 (λ 232 nm) and 15.86 + 0.52 (λ 258 nm), while in λ 312 nm, λ 368 nm and λ 656 nm that obtained from glucose were 11.59 + 0.28, 7.22 + 0.44 and 1.50 + 0.05. At nitrogen source experiment, the result showed that Mesophilobacter sp. grew rapidly in the medium with yeast extract. The pigment has a maximum absorbance at five wavelengths, namely λ 232 nm, 258 nm, 312 nm, 368 nm, and 658 nm. The average concentration of cells and pigment, showed that yeast extract is the best nitrogen source in cell growth and pigment formation (p <0.05). The highest average P is 12.49 + 0.22 (λ 232 nm); 12.86 + 0.21 (λ 258 nm); 11.09 + 0.56 (λ 312 nm) ; 11.88 + 0.97 (λ 368 nm) and 1.29 + 0.04 (λ 656 nm).
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Judul: Pengaruh penambahan pupuk oleofilik terhadap pertumbuhan bakteri heterotrofik dan bakteri pemecah minyak dalam perairan tercemar minyak: Eksperimen mesokosm
Abstrak: Berbagai kasus pencemaran minyak di laut sudah banyak terjadi yang mengakibatkan keseimbangan ekosistem menjadi terganggu. Salah satu alternatif untuk menanggulangi pencemaran minyak dapat dilakukan dengan pendekatan secara biologi dengan cara biodegradasi. Dalam hal ini digunakan aktivitas bakteri untuk mendegradasi minyak yang ada di perairan. Penelitian ini bertujuan untuk mengetahui pertumbuhan bakteri heterotrofik dan hidrokarbonoklastik akibat penambahan pupuk oleofilik dalam lingkungan mesokosm yang dicemari minyak. Selain itu akan dilihat fluktuasi beberapa parameter fisika-kimia perairan, seperti suhu, pH, kadar oksigen terlarut (DO), serta konsentrasi fosfat dan nitrat. Tujuan lain dari penelitian ini adalah untuk melihat apakah penambahan pupuk oleofilik berpengaruh terhadap biota lain (fitoplankton) dengan menganalisa kandungan klorofil-a nya. Penelitian ini dilakukan pada tanggal 720 September 1998 di Perairan Teluk Pelabuhan Ratu dengan menggunakan teknik mesokosm. Terdapat empat mesokosm (A, B, C dan D) dengan volume total masing-masing ± 5300 liter air laut. Ke dalam setiap mesokosm dimasukkan minyak mentah dengan kadar 100 ppm. Perlakuan pada penelitian ini adalah dengan menambahkan masing-masing 3,2 ppm pupuk oleofilik pada mesokosm B, 10 ppm pupuk oleofilik pada mesokosm C dan 32 ppm pupuk oleofilik pada mesokosm D. Mesokosm A adalah mesokosm kontrol karenanya tidak diberi penambahan pupuk oleofilik. Sampel bakteri heterotrofik dan hidrokarbonoklastik diambil sebanyak lima kali, pada hari ke-0, ke-1, ke-2, ke-4 dan ke-8. Sedangkan pengambilan sampel air untuk analisa klorofil-a, nutrien dan parameter fisika-kimia perairan dilakukan setiap hari, sebanyak 9 kali pengambilan, yakni pada hari ke-0 sampai hari ke-8...
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Judul: Truncated Stop Loss as a Optimal Solution of Reinsurance Agreement in One-Period Model
Abstrak: Reinsurance is one of risk management efforts of an insurance company, which is called the cedent. Similar with insurance, reinsurance constitutes the cedent to pay the premium. We consider one-period reinsurance model and derive a rule which minimizes the ruin probability of the cedent for a fixed reinsurance premium. Therefore, it is needed to construct an optimal reinsurance agreement for the cedent. The premium is calculated according to four different principles, i.e. economic, generalized zero-utility, Esscher, and mean-variance principles. Stop loss is a reinsurance contract which protect the insurance company for losses that exceed a certain amount. The result of this research shows that a truncated stop loss is an optimal agreement in the class of all reinsurance contracts with various premiums calculated using above mentioned principles.
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