Judul: Adaptation of saccharomyces cerevisiae to cassava acid hydrolisates for bioethanol production.
Abstrak: Acid hydrolisates of cassava contain toxic substances i.e. 3,55 g/l HMF and 0,72 g/l furfural to ethanol producing yeast, Saccharomyces cerevisiae. This study is aiming at screening four strains of S. cerevisiae for their tolerance capacity to that acid hydrolisates. Out of four strains, S. cerevisiae IPBCC 05.548 showed the highest tolerance on the bases of ethanol production. It produced 4,1% (b/v) ethanol. Prior to adaptation, optimum sugar concentration and starter dosage were determined in sequence. Out of 15%, 18%, 20% and 24% concentration. S. cerevisiae IPBCC 05.548 showed the highest ethanol production (4,10% b/v) at 15% of total sugar. Among starter dosage (1, 2 and 3 times of 0,23% of sugar concentration), that were tested on optimal sugar concentration indicated that the twice of dosage was the best for ethanol production. Adaptation was then performed for 72 hours for each cycle. Of the cycles, the 9th cycle (648 hours) showed the highest specific growth rate (0,14g.h-1) as well as ethnol yield (4,13% b/v). Comparison of the adapted strain to unadapted strain proved that the adapted strain produced 30,78% higher ethanol yield than those of unadapted strain.
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Judul: Fermentasi Repeated-batch Menggunakan Saccharomyces cerevisiae Terimobilisasi pada Ampas Singkong untuk Produksi Bioetanol
Abstrak: Bioetanol is ethanol produced from biomass containing sugar, starch or cellulose through fermentation by microorganisms, one of them is Saccharomyces cerevisiae. Improvement of ethanol production can be done by using immobilized cell. The potency of cassava bagasse is big, but has not been optimally utilized, so in this research it was used as a carrier for imobilization. This research is aim to study bioethanol production from cassava starch in repeated-batch fermentation by S. cerevisiae immobilized on cassava bagasse. Research method consists of starch extraction, starch hydrolysis, cassava bagasse treatment by HCl 3% (v/v), immobilization of S. cerevisiae on cassava bagasse, and fermentation by repeated-batch method. The resulting yield of starch was 25.10% (w/w) and conversion efficiency of starch to hydrolyzed starch was 98.94%. The total cell of S. cerevisiae which adsorp on the surface of the carrier was 0.75 x 1011 sel/g carrier. Selection of the best ratio of carrier to the media fermentation found in the ratio of 6% which produced ethanol concentration of 49.23-68.75 g/L, productivity 2.05-2.86 g/L/h, yield 0.40-0.50 g/g, sugar conversion 83.16-99.86%, and efficiency 78.20-97.02%. The resulting ethanol concentration was 42.72-63.66 g/L, productivity 1.78-2.66 g/L/h, sugar conversion 90.80-95.74%, yield 0.33-0.47 g/g, and efficiency 65.91-93.13%. Selection of the best sugar concentrations have been observed through repeated-batch fermentation with 10 cycles. The research showed that best sugar concentration was obtained by using 160 g/L and ethanol produced was 71.91 g/l. This research showed that imobilized cells can improve productivity by 2-3 times in comparison with the fermentation by using free cells.
Keyword: Saccharomyces cerevisiae, repeated-batch, fermentation, cassava bagasse, bioethanol

Judul: Teknik penentuan posisi bintang berdasarkan pelat foto overlapping
Abstrak: Bintang adalah salah satu objek langit yang menarik untuk diamati. Untuk itu, pengetahuan tentang posisi bintang sangat diperlukan. Posisi bintang di langit dapat dihitung melalui foto bintang. Fotografi astronomi atau astrometri merupakan ilmu yang mempelajari metode untuk menentukan posisi bendabenda langit seperti bintang berdasarkan pelat foto (Kamp, 1967). Sebuah pelat foto berisi citra bintang-bintang yang sudah diketahui posisinya berdasarkan katalog dan citra bintang-bintang yang belum diketahui posisinya. Posisi bintang yang ada di katalog dinyatakan dengan (a,3). Bintang yang belum diketahui posisinya lebih banyak jumlahnya daripada bintang yang sudah diketahui posisinya. Citra bintang pada pelat foto berupa sebuah titik dalam bentuk tetap. Posisinya pada pelat merupakan hasil pengukuran pada bidang kartesius dan dinyatakan dengan (1;,fl). Hasil pengukuran tersebut kemudian direduksi menjadi koordinat terukur (x,y). Hubungan antara (a,3) dan (x,y) didekati dengan sebuah deret dengan konstanta-konsranta deret merupakan konstanta pelat. Nilai konstanta pelat diperoleh dengan menggabungkan hasil pengukuran posisi bintang pada masing-masing pelat menjadi sebuah persamaan normal (Jefferys, 1963). Hasil akhir dari gugus persamaan normal tersebut dijabarkan dalam bentuk nOlasi matriks partisi dan berupa sebuah sistem persamaan linier Ax = b di mana A adalah matriks jarang, dan x merupakan konstanta pelar yang akan dicari nilainya. Untuk menyelesaikan sistem persamaan linier terse but digunakan metode transformasi given. Konstanta pelat yang sudah diperoleh dengan menyelesaikan sistem persamaan linier di atas, kemudian disubtitusi ke sebuah persamaan untuk memperoleh posisi bintang yang tidak tercantum dalam katalog. .
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