Judul: Aktivitas Antioksidasi Campuran Ekstrak Daun Sirih Merah dan Kulit Kayu Manis
Abstrak: Piper crocatum leaves and Cinnamomum burmanii bark are medicinal plants. The plants compounds as antioxidant. The objectives of this research are to determine the antioxidant activity of the extract mixture P. crocatum and C. burmanii with Thiobarbituric acid method (TBA) and 1,1-diphenyl-2-picrylhydrazyl method (DPPH). Extraction process of P. crocatum and C. burmanii was conducted separately by using the solvent water. P. crocatum extract mixed with extract of C. burmanii with a ratio of 5:0, 4:1, 3:2, 2.5:2.5, 0:5. The results showed that the 3:2 concentration 200 ppm (61%) had the same inhibitory activity as vitamin E against malondialdehida formation. Meanwhile, formula 2.5:2.5 concentration 25 ppm (59%) had the same inhibitory activity as vitamin E against DPPH radical inhibition
Keyword: Cinnamomum burmanii., Piper crocatum, antioxidative activity

Judul: Pendekatan Metabolomik terhadap Aktivitas Antioksidan Ekstrak dan Fraksi Daun Sirih Merah (Piper crocatum Ruiz & Pav)
Abstrak: Tanaman herbal yang memiliki potensi sebagai antioksidan adalah sirih merah (Piper crocatum Ruiz & Pav). Daun sirih merah (Piper crocatum Ruiz & Pav) mengandung flavanoid, tanin, dan alkaloid. Secara empiris zat aktif tersebut berperan sebagai antioksidan. Penelitian ini bertujuan menentukan aktivitas antioksidan tertinggi dari ekstrak dan fraksi daun sirih merah. Penelitian ini menganalisis peranan fenolik, tanin dan flavonoid terhadap aktivitas antioksdian DPPH dan MDA menggunakan analisa multivariat. Aktivitas antioksidan tertinggi terdapat pada fraksi n-heksan dengan nilai IC50 72.85 μg/mL. Analisis PCA total fenolik, aktivitas antioksidan mampu mengelompokkan sampel berdasarkan nilai IC50 dengan nilai PC total sebesar 84.04%. Fraksi n-heksana memiliki komponen tanin yang tinggi sebesar 98 mg/g dan aktivitas antioksidan MDA yang tinggi dengan IC50 72.85 μg/mL. Fraksi etil asetat memiliki komponen flavonoid yang tinggi sebesar 107.5 mg/g dan aktivitas antioksidan DPPH yang tinggi dengan IC50 13.14 ppm, sedangkan ekstrak etanol dan air memiliki kadar tanin sebesar 86 mg/g dan 32 mg/g dan flavonoid sebesar 47.72 mg QE/g dan 14.11 mg QE/g dan termasuk antioksidan sedang.
Keyword: Daun Sirih Merah, Antioksidan, Analisis PCA, Komponen

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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