Judul: Aktivitas Antioksidan, Kadar Fenolik, dan Flavonoid Tumbuhan Suruhan (Peperomia pellucida L. Kunth)
Abstrak: Suruhan (Peperomia pellucida L.Kunth) is the bush had widespread in Indonesia and has efficacy as arthritis pain relief, anticancer, and antibacterial. The aim of this study was testing the activity of suruhan’s herb extracts as natural antioxidants and measured the total phenolic and flavonoid content in suruhan. The sample used in the form of 70% ethanol extract and aqueous extract of the suruhan. The extract obtained by maceration method and tested antioxidants with DPPH method and then tested the content of total phenolic and flavonoid extracts and analyzed the correlation of these compounds to antioxidant activity. The yield of 70% ethanol extract was 20.43 ± 3.33% whereas the yield of aqueous extract was 10.03 ± 2.85%. Both of extract has produced the antioxidant activity of free radical DPPH capture. IC50 values of aqueous extract of 256.67 ± 21.65 ppm, followed by ethanol extract of 297.79 ± 17.75 ppm. Total phenolic content of aqueous extract was 755.79 ± 65.87 mgTAE/g and ethanol extract was 622.46 ± 179.43 mg TAE/g. Total flavonoid content of ethanol extract was 4.058 ± 0.352 mg QE/g and aqueous extract was 0.67 ± 0.352 mg QE/g extract for aqueous. The phenol content have linier correlation with their antioxidant activity but the flavonoid content didn’t have correlation with antioxidant activity.
Keyword: 

Judul: Antioxidant, HMG-CoA Reductase Ihibition activity, and Chemical Compound Identification of Surian (Toona sinensis) Leaves Extract.
Abstrak: Surian (Toona sinensis) is forest plant that are widespread in Asia. This plant only used and known as a comodity for carpentry in Indonesia but in other nation surian is known as spices and traditional medicine because of its natural antioxidant potential. The objective of this study was assayed total phenolic content, total flavonoids content, antioxidant activity, HMG-CoA reductase inhibition activity and to analyze chemical compound from Surian leaves extract. Surian leaves were extracted by water and ethanol solvent. Water extraction was conducted by reflux in 90 oC then ethanol extraction was conducted by maceration, which is through various concentration 70%, 80%, 90%, and 96% of ethanol. Total Phenolic content was determined according to the Folin–Ciocalteu method using miligram of gallic acid equivalent and total flavonoid content was evaluated using aluminium chloride by compared with quercetin standard. Antioxidant activity of the water and ethanol extracts was evaluated using DPPH radical scavenging method. Inhibition of HMG-CoA reductase was assayed in vitro using single concentration inhibition with atorvastatin as comparison. Total phenolic and flavonoid content of ethanol 90% extract and ethanol 96% extract had higher amount than the other. The ethanol 96% extract had the strongest DPPH inhibition conccentration 50% (IC50), which is 3.38 μg /mL while ascorbic acid is 3.90 μg /mL as a comparison. The ethanol 96% extract also had highest inhibition HMG-CoA reductase activity which is 79.13% and this activity strongest in water fraction from this extract with inhibition 91.49% while atorvastatin as a comparsion is 92.45%. Antioxidant and inhibition ezyme activity had strong corelaltion with total flavonoid content. Chemical compound by LC-MS assay mostly are counted in the flavonoids group.
Keyword: Antioxidant, Flavonoids, HMG-CoA reductase, Toona sinensis

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.
Keyword: