Judul: Aktivitas Antioksidan dan Inhibisi Enzim α Glukosidase serta Toksisitas Ekstrak Air-Etanol dan Heksan Anggrek Merpati (Dendrobium cruminatum SW)
Abstrak: Dendrobium cruminatum are anggrek that grow in almost all regions of Indonesia. Dendrobium cruminatum leaves contain flavonoid compounds that are useful as an antioxidant and antidiabetic. This study aims to determine the ability of the anggrek merpati extract as an antioxidant and it’s potential to inhibition activity of α-glucosidase enzyme and also as a compound that toxic to the larvae of shrimp Artemia salina Leach with different solvents. The antioxidant activity was measured by using DPPH method and antidiabetic measured by the formation of p-nitrifenol-α-D-glukopiranosida (p-NPG) were measured with a spectrophotometer at a wavelength of 410 nm. The results of antioxidant activity and cytotoxicity testing showed that the best solvent used for the extraction of anggrek merpati leaf is water solvent with IC50 value of 153.565 μg / mL and the level of cytotoxicity was 889.641 mg / mL. whereas the activity of the inhibition of α-glucosidase enzyme is owned by the highest percentage of etanol by 64% at a concentration of 1000 μg / mL or IC50 value of 435 μg / mL.
Keyword: Bogor Agricultural University (IPB), antidiabetic and cytotoxicity., antioxidant, Dendrobium cruminatum

Judul: Aktivitas Antihiperglikemik dan Antioksidan Buah Bakau Merah (Rhizophora stylosa Griff.)
Abstrak: Red mangrove (R. stylosa) is one of rhizoporaceae which has been widely used as antidiabetic drugs. One of the way how to prevent and treat diabetic is by inhibiting activity of the enzyme α-glucosidase. The purpose of this research was to determine the antihyperglycemic activity of crude extract of the red mangrove (R. stylosa) fruit. The research was performed in several steps there were characterization of mangrove fruit, extraction (maceration), proximate test (AOAC 2005), toxicity test (BSLT), antihyperglycemic test (α-glucosidase inhibition), antioxidant test (DPPH), and phytochemical test (Harborne 1987). The result showed that the methanol extract had the highest yield compared to other extracts equal to 3.45%. The methanol extract possessed the most toxic with LC50 values of 116.96 ppm. Ethyl acetate extract had the highest value of α-glucosidase inhibition (IC50) in the amount of 285.56 ppm, followed by methanol extract of 474.97 ppm, and n-hexane extract of >15000 ppm. The antioxidant test result of ethyl acetate extract showed IC50 value 79.71 ppm. Phytochemical test of ethyl acetate extract showed positive results on phenol hydroquinone, flavonoid, steroid and triterpenoid
Keyword: Bogor Agricultural University (IPB), α-glucosidase, toxicity, red mangrove, phytochemical, Antioxidant

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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