Judul: Analisis Kestabilan Mangsa-Pemangsa Lotka-Volterra dengan Allee Effects
Abstrak: Allee effects adalah hubungan positif antara kepadatan populasi dan laju pertumbuhan. Tujuan dari penulisan karya ilmiah ini ialah mempelajari pengaruh allee effects terhadap kestabilan sistem dan menganalisis perubahan kestabilan titik tetap dari model tersebut. Model yang dibahas terdiri dari dua model, yaitu model tanpa allee effects dan dengan allee effects. Perbedaan dari kedua model tersebut adalah terdapat besaran allee effects pada model dengan allee effects. Simulasi dilakukan dengan mengambil parameter yang berbeda untuk masing- masing kasus. Hasil simulasi menunjukkan bahwa ada pengaruh allee effects terhadap kestabilan, yaitu diperlukan waktu yang lebih lama untuk mencapai kestabilan. Meningkatnya allee effects akan menurunkan kepadatan populasi. Allee effects juga mengubah sifat kestabilan dari simpul stabil menjadi spiral stabil.
Keyword: Allee effects, Stability, Population density, Growth rate, Steady state, Kepadatan populasi, Laju pertumbuhan, Titik tetap, Penentuan titik tetap

Judul: Stability Analysis of Predator-Prey Model of Leslie-Gower with Allee Effect and Hunting Cooperation
Abstrak: Model dalam penelitian ini adalah model mangsa-pemangsa Leslie-Gower dengan mempertimbangkan adanya efek Allee pada populasi mangsa dan kerja sama perburuan pada populasi pemangsa. Tujuan dari penelitian ini adalah mengkaji pengaruh koefisien kerja sama perburuan dan tingkat efek Allee pada model. Metode yang digunakan adalah dengan mencari serta menganalisis kestabilan dari titik tetap dan melakukan simulasi numerik, serta menunjukkan keberadaan bifurkasi Hopf. Model ini memiliki empat titik tetap dengan sifat kestabilannya dipengaruhi oleh nilai parameter. Peningkatan nilai tingkat efek Allee mengakibatkan populasi mangsa-pemangsa mengalami kepunahan. Penurunan nilai tingkat efek Allee mengakibatkan kedua populasi dapat hidup berdampingan (koeksistensi) dan terhindar dari kepunahan. Perubahan nilai koefisien kerja sama perburuan mengakibatkan kedua populasi koeksistensi. Terdapat titik tetap yang berhubungan dengan perubahan sifat kestabilan dan munculnya siklus limit, yang menandai terjadinya bifurkasi Hopf., The model in this study is the Leslie-Gower predator-prey model by considering the Allee effect in the prey population and hunting cooperation in the predator population. The purpose of this study is to examine the effect of hunting cooperation coefficient and the level of Allee effect on the model. The method used is to find and analyze the stability of the fixed point and perform numerical simulations, and show the existence of Hopf bifurcation. The model has four fixed points with stability properties influenced by parameter values. An increase in the value of the Allee effect level results in the extinction of the predator-prey population. A decrease in the value of the Allee effect level results in both populations being able to coexist and avoid extinction. A change in the value of the coefficient of hunting cooperation results in the coexistence of the two populations. There are fixed points that related with the changes in stability properties and the emergence of limit cycles, which indicate the occurrence of Hopf bifurcation.
Keyword: Allee effect, Hopf bifurcation, hunting cooperation, Leslie-Gower, predator-prey

Judul: Pemurnian dan karakterisasi protein inhibitor RNA helikase virus hepatitis C
Abstrak: Hepatitis C virus (HCV) infection is the second most common chronic viral infection in the world with global prevalence. This infection is contribution to chronic hepatitis and liver cirrhosis, often leading to hepatocellular carcinoma. There is no effective drug and vaccine available against HCV. The current standard treatment, a combination of pegylated interferon-α with ribavirin, is limited by its suboptimal response rate in a significant patient population, side effects, and affordability. Therefore, development of effective drug is needed. One approach to find out the candidate of antiviral drug is to discover the inhibitor of enzyme that essential for virus replication, such as RNA helicase. Streptomyces chartreusis 5-095 produce the inhibitor of HCV RNA helicase. The aim of this study was to purify the protein inhibitor which has inhibition activity against ATPase activity of RNA helicase HCV from S. chartreusis 5-095. The supernatant of culture S. chartreusis 5-095 exhibited high inhibiton activity against ATPase activity of RNA helicase HCV (approximately 72%) at 10 days of incubation. The extracellular protein inhibitor was partially purified by procedures of precipitation with ammonium sulfate to 65% saturation and gel filtration (Sephadex G50) using methanol water solution (4:6) as an eluen. The purity of protein inhibitor was monitored by SDS PAGE. The protein inhibitor showed a relative molecular mass were estimated to be 14 kDa and increased the purity 23,08 fold than those of the crude protein. The specific activity and IC50 after purification were 13,1338 U/mg and 0,0767 mg/mL, respectively. The activity of purified protein inhibitor showed its stability over pH range from 5-8 and optimum at pH 7,4. The inhibition activity showed its stability up to 70% at temperature 100 oC. The purified protein inhibitor relatively stable its activity at storage in the range of -20 oC to room temperature for 35 days.
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