Judul: Efektivitas fiksasi N2 dan oksidasi metan kultur campuran bakteri metanotrof asal sawah
Abstrak: Sebagian besar emisi CH4 di lahan sawah yang tergenang diproduksi oleh bakteri metanogen dan sebanyak 80 % dari CH4 tersebut dioksidasi oleh bakteri metanotrof. Selain kemampuan mengoksidasi metan, metanotrof juga memiliki kemampuan memfiksasi nitrogen. Empat isolat metanotrof dengan kemampuan fiksasi nitrogen (BGM 1, BGM 3, BGM 5, dan BGM 9) masing-masing dikombinasikan dengan isolat metanotrof yang memiliki aktivitas oksidasi metan tinggi (SKM 14) untuk mendapatkan formulasi metanotrof yang tinggi aktivitas fiksasi nitrogen dan oksidasi metan-nya. Kemampuan fiksasi nitrogen diukur dari kadar amonium yang diakumulasikan dalam medium pertumbuhannya dan aktivitas reduksi asetilen (ARA). Akumulasi amonium tertinggi dicapai oleh kultur BGM 1 untuk kultur tunggal (1,86 μM amonium), dan kultur BGM 3/BGM 9 untuk kultur kombinasi (4,905 μM amonium). Aktivitas nitrogenase tertinggi ditunjukkan oleh kombinasi BGM 1/SKM 14 (11,27 μmol/ml kultur/hari), sedangkan aktivitas oksidasi metan tertinggi dicapai oleh kultur campuran BGM 5/BGM 9 (18,20 ppm/ml kultur/hari).
Keyword: Metan, Bakteri metanotrof, ARA, Fiksasi nitrogen, Oksidasi metan, Bogor Agricultural University, Institut Pertanian Bogor, IPB

Judul: Efektivitas fiksasi N2 dan oksidasi metan kultur campuran bakteri metanotrof asal sawah
Abstrak: CH4 emissions in a rice field and wetlands is mostly produced by methanogenic bacteria and 80% of the CH4 is oxidized by methanotrophs. Besides of their ability to oxidize methane, methanotrophs also have ability to fix nitrogen. Four selected isolates of methanotrophs which had high nitrogen fixation activity i.e.(BGM 1, BGM 3, BGM 5, and BGM 9 isolates were combined with SKM 14 isolate which had high methane oxidation activity to obtain ideal formulations of the methanotrophs that have high activity of nitrogen fixation and methane oxidation activities. Nitrogen fixation activity was determined by measuring accumulated ammonium in medium and acetylene reduction assay (ARA). The highest concentraion of ammonium on single culture of methanotrophic bacterium was performed BGM 1 isolate (1,86 μM ammonium), and mixed culture of BGM3 and BGM9 isolates had the highest ammonium accumulation (4,905 μM ammonium). The highest nitrogenase activity was performed by mixed culture of BGM1 and SKM14 isolates, it was 11,27 μmol/ml cultures/hour. Whereas the higest methane oxidation was performed by mixed culture of BGM5 and BGM9 isolates, it was 18,20 ppm /ml cultures /day.
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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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