Judul: Isolasi dan Seleksi Bakteri Termofilik Pereduksi Kromium Heksavalen dari Limbah Pengolahan Batik
Abstrak: Kromium heksavalen (CrVI) dalam keadaan teroksidasi bersifat toksik karsinogen pada manusia. Kromium banyak digunakan dalam berbagai industri, sehingga Cr(VI) juga dapat ditemukan pada limbah-limbah hasil dari industri tersebut. Limbah logam berat Cr(VI), merupakan salah satu jenis limbah berbahaya, karena tingginya toksisitas Cr(VI) yaitu jauh lebih tinggi dibandingkan toksisitas (III). Penelitian ini dilakukan untuk mengisolasi bakteri alami pada limbah pengolahan batik yang bepotensi mereduksi Cr(VI) karena memiliki gen penyandi enzim kromat reduktase. Identifikasi gen penyandi kromat reduktase dilakukan dengan menggunakan metode qPCR. Hasil menunjukkan bahwa diperoleh 3 (tiga) isolat yaitu isolat Bacillus sp., Pseudomonas sp. dan Geobacillus sp. yang memiliki gen penyandi enzim kromat reduktase. Oleh karena itu terhadap ketiga isolat tersebut dilakukan uji aktivitas reduksi Cr(VI), Hasil analisis qPCR, menunjukkan bahwa isolat Bacillus sp. diduga memiliki aktivitas reduksi paling baik. Selanjutnya hasil uji aktivitas reduksi Cr(VI) oleh ketiga isolat menunjukkan bahwa aktivitas tertinggi terjadi pada suhu inkubasi 50°C, yang diikuti oleh 40°C dan 30°C. Aktivitas reduksi isolat Bacillus sp.optimal pada pH 7 dengan nilai reduksi 97 %,isolat Pseudomonas sp.optimal pada pH 5dengan nilai reduksi mencapai 59.36 % dan aktivitas reduksi isolat Geobacillus sp. optimal pada pH 5 dengan nilai reduksi mencapai 59 % Cr (VI) yang tereduksi. Analisis optimasi terhadap aktivitas reduksi Bacillus sp.menggunakan Surface Respon Analysis(SRA) Minitab 16 diperoleh hasil perlakuan pH, konsentrasi dan suhu inkubasi menunjukkanperbedaan yang signifikan (P< 0.05). Hasil tersebut menunjukkan bahwa masing-masing perlakuan yaitu pH, konsentrasi dan suhu inkubasi berpengaruh terhadap aktivitas reduksi. Interaksi suhu-konsentrasi dan interaksi pH-konsentrasi juga memberikan hasil yang berbeda nyata (P<0.05), yang berarti kedua interaksi tersebut berpengaruh terhadap aktivitas reduksi.Hasil analisis optimasi aktivitas reduksi padaPseudomonas sp.menggunakan Minitab 16 menunjukkan bahwa perlakuan pH,konsentrasi kromium, suhu inkubasidan interaksi konsentrasi kromium-suhu berpengaruh nyata (P< 0.05). Sedangkan uji statistik terhadap aktivitas reduksi isolat Geobacillus sp. menunjukkan perlakuan suhu inkubasi berbeda nyata (P< 0.05), artinya perlakuan suhu inkubasi memberikan pengaruh yang signifikan terhadap aktivitas reduksi. Interaksi suhu-konsentrasi juga memberikan hasil yang berbeda nyata (P<0.05), yang berarti interaksi antara suhu dan konsentrasi juga memberikan aktivitas reduksi yang berbeda. Diperoleh 3 (tiga) isolat, yaitu isolat dari Bacillus sp., Pseudomonas sp., dan Geobacillus sp. yang memiliki gen penyandi kromat reduktase. Hasil karakterisasi dengan qPCR menunjukkan isolat Bacillus sp. berpotensi lebih baik dibandingkan dengan isolat Pseudomonas sp. dan Geobacillus sp. Aktivitas reduksi Cr(VI) isolat Bacillus sp.1a bersifat termofilik,optimum pada pH .
Keyword: Kromat, kromat reduktase, Kromium heksavalen

Judul: Identifikasi Isolat Bakteri Tahan Krom(VI) dan Pengujian Aktivitas Enzim Krom(VI) Reduktase
Abstrak: Cr(VI) (chromate) is a toxic, soluble environmental contaminant. A Gram-negative, Cr(VI)-resistant bacterium, has been isolated from effluent of electroplating wastewater treatment reactor. This strain had maximum identity value as high as 96% to Ralstonia pickettii and Ralstonia sp. M2S3. This value indicated that the strain was a species of Ralstonia genera. Because of this reason, the strain was designated as Ralstonia sp. Cr6NS. Ralstonia sp. Cr6NS was able to grow aerobically in 250 ppm Cr(VI) and had Cr(VI) reducing-capacity as high as 4,11 x 10-8μg Cr(VI)/hour/cell. From the study of enzymatic activity, Ralstonia sp. Cr6NS showed the activity of Cr(VI)-reductase both in periplasmic and sitoplasmic content. The highest activity was found in periplasmic matrix. However, the strain seemed not secreting this enzyme to the external medium.
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Judul: The Effects of Variance of Interest rate to Variance of Annuity Future Values
Abstrak: Time value of money is a concept that refers to the difference of the value of money due to time difference. The value of money for present time would not be the same as the value of money in the future. The value of money for present time is called as Present Value (PV) of the money and the value of money for future time is called Future Value (FV) of the money. Determination the value of money, for present and future time, depends on the time and rate of return. The value of money is determined by several factors such as inflation, fluctuation of interest rates, and government policy in securities and taxation. Due to fluctuation of the value of money we need a FV formulation, it is useful for knowing whether an investment can be profitable or not, and this information is useful also in budget analysis. Annuity is defined as a series of payments made for a specific period. The payment, fixed or varied, can be made at the beginning or at the end of the period. Annuity paid at the beginning of the period is called annuity-due and annuity paid at the end of the period is called immediate annuity-certain. The accumulated value of the annuity after few years later is called as a final value or a future value. Burnecki et al. (2003) have discussed about the FV of a fixed-rate annuity in which payments are made according to the arithmetic or geometric series. They have also examined FV for annuities in which payments are made according to arithmetic or geometric series with random rates of interest. This paper examines FV for annuity-due in which payments are made according to arithmetic or geometric series with interest rates as a random variable, which is normal distribution ,  . Future value formula is expressed in recursive form. FV for annuity-due which payments are made according to the arithmetic or geometric series with random rates of interest is calculated by theoretical way and simulation way. The random rates of interest is denoted as k k i  i  , where k i an independent random variable; i is a constant and k  is a random variable which has normal distribution ,  . By using the determined parameters, a sequence of random rates of interest are generated for theoretical calculation. Meanwhile for the simulation, the random rates of interest is generated 1000 times for the simulation. The generated data give mean value, variance, and standard deviation. Moreover, error of mean value, variance, and standard deviation from the theoretical and simulation results are calculated. Error calculation uses Symmetric Mean Absolute Percentage Error (SMAPE). The smaller the value of SMAPE is the more accurate the simulation. The interest rate variances are varied from 0.000036 to 0.0001 to study the relationship between variance of rates of interest and variance of future value. The theoretical and simulation results show that when the variance of random rates of interest increases, then the variance of FV increases linearly. FV of the annuity-due in
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