Judul: Fraksionasi Ekstrak Kulit Petai Berpotensi Antioksidan
Abstrak: Many medicinal plants have been used in traditional treatment and are known to be potencial as antioxidant. Petai is one of the medicinal plants having high antioxidant activity. This study aimed to study the cytotoxicity and antioxidant activity of the exterior and interior parts mixture of petai seed coat with brine shrimp lethality test and 1,1-diphenyl-2-picrylhydrazyl methods. Petai seed coat was extracted with methanol and liquid-liquid partitioned by using n-hexane, chloroform, and ethyl acetate. The 50% lethal concentration (LC50) values of ethyl acetate and water fractions were 49.51 and 118.01 mg L-1, respectively. These results showed that both fractions were potencial as active compounds and toxic. Ethyl acetate fraction had the highest antioxidant activity with the 50% inhibition concentration (IC50) value of 2 mg L-1. Water and solid fractions had IC50 values of 5.37 and 4.05 mg L-1, respectively. Gallic acid was used as positive control and gave IC50 value of 0.48 mg L-1. Based on these results, all 3 fractions of petai seed coat extract had very high antioxidant activities.
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Judul: Aktivitas Antibakteri Ekstrak Kulit Petai (Parkia speciosa Hassk.) Terhadap Bakteri Escherichia coli dan Staphylococcus aureus
Abstrak: Parkia speciosa Hassk. is one of edible plants that not developed as medicinal plants yet.The purpose of this research is to study antibacterial activity of peel extract to Staphylococcus aureus and Escherichia coli bacteria with gel diffusion (well method). Peel extract that used in this research were from extraction of n-hexane, ethyl acetate, and ethanol 70%. The concentration were 50, 100, 150, 200, 250, and 300 mg/mL for every solvent. The result of this research showed that ethyl acetate extract has the highest antibacterial activity with 404,25% of 10 mg/mL streptomycin’s antibacterial activity agains Staphylococcus aureus, and 279,12% of 10 mg/mL streptomycin’s antibacterial activity agains Escherichia coli. TLC result showed that ethyl acetate extract with toluene:ethyl acetate (93:7) as solvent has eight spots under 254 nm UV that was mean ethyl acetate extract of petai peel consisted of eight compound. The result of Analysis of Variance with SPSS 16 program for windows showed that variance of solvents and concentration were significantly different for inhibition areas
Keyword: Bogor Agricultural University (IPB), TLC, Staphylococcus aureus, Parkia speciosa Hassk, Escherichia coli, antibacteria

Judul: Bifurkasi Hopf pada Model Siklus Bisnis Kaldor Kalecki tanpa dan dengan Waktu Tunda
Abstrak: Business cycle model is one of dynamical system models in economic. One of the business cycles model is Kaldor-Kalecki model. Kaldor-Kalecki business cycle model that is written in delayed defferential equations, is a business cycle model that involves gross product and capital stock of a company. In this paper Kaldor-Kalecki business cycle model is analyzed using both nondelay and delay in time of capital stock. By Taylor expansion for the time delayed model, an analysis of stability around the fixed points has been done. Furthermore, by using Hopf bifurcation theorem, it can be shown that there exists periodic orbits and limit cycle. In the nondelayed model, changing the parameter of goods market could lead to the occurrence of Hopf bifurcation and the existence of limit cycle. Similarly, for the delayed model, it has been shown that changing the time delay parameter may result in the occurrence of Hopf bifurcation and limit cycle.
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