Judul: Biosintesis dan karakterisasi nanopartikel silika (SiO2) dari sekam oleh Fusarium oxysporum
Abstrak: Silica nanoparticles have many advantages such as large surface, heat resistance, mechanical strength, and inert. Therefore has been used as a precursor catalyst, an adsorben, and a composit filter. Biosynthesis is a method to find the nanoparticles through enzymatical mechanism from microbe. This research aims to produce the silica nanoparticles by F.oxysporum with a phase growth and an amount of rice husk as substrate optimization. F.oxysporum is grown in a media pH 4-6, incubation temperature 27ºC, and 200 rpm aeration system. The presence of extracellular enzymes F.oxysporum views based on their ability in reducing the silica which is contained in the rice husk. The number of optimum substrate is determined by the two treatments, 2.5 gram and 5 gram of rice husks. The F.oxysporum biomass has been harvested in 72th hour, when the cells entered the stationary phase based on the growth curve. SEM analysis results for both types of treatments shows the number of particles agregate each other and have undifferent particle size with variations in size between 200-1000 nm. The three highest peaks are found in the FTIR absorption spectrum which is located at peaks 3408.18 cm-1 for the group H2O, peaks 1639.04 cm-1 for the group CO32-, and peaks 1078.71 cm-1 for the group Si-O-Si. The husk with F.oxysporum treatment indicated to be changed from the structure basic forms (amorphous) to the crystalline silica nanoparticles (crystoballite) based on XRD analysis.
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Judul: Ekstrasi Silika dari Sekam Padi dengan Metode Pelarutan dan Pengendapan Silika serta Analisis EDX dan FTIR
Abstrak: Estimated amount of rice production in 2013 is 69.27 million tons. Compared to rice production in 2012 increased by 0.21 million tons. Some researchers have done the extraction of silica from rice husk through process using alkali solvent and acid precipitation of silica. The aim of this research is to extract silica using alkali solvent and to study the effects of alkali solvent toward the purity and the molecular structure of silica. The procedure of this research covers two phases namely carbonization and silica extraction of rice husk. The largest rendemen obtained is 22.59%, when 20% NaOH solution was added. The largest purity of silica (92.01%) were obtained when 20% KOH solution added with potasium and rubidium act as inpurities. FTIR spectra on 463-486 cm-1, 617 cm-1, 787-802 cm-1, and 1095-1103 cm-1 waves number show the presence of Si-O-Si (siloksan) group, as well as on 1643 cm-1 and 3448-3464 cm-1 waves number shows the existence of Si-OH (silanol) group or a molecule of water. The value of symmetry streching vibration spring constant Si-O is 948.891 – 1017.991 N/m
Keyword: Siloksan., Silica, Silanol, Rice husk, FTIR

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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