Judul: Green Synthesis Silver Nanoparticles with Terminalia catappa Leaf Extract as Reducing Agents
Abstrak: The objective of this research was to synthesis silver nanoparticles (AgNPs) by using Terminalia catappa (TC) leaf extract as reducing agents. AgNPs was prepared by the reaction of 1mM silver nitrate solution with fresh leaves extraction ratio of 40:1 (v/v). Various concentration of polyvinyl alcohol (PVA) : 0%, 1%, and 2% were studied. The result showed that AgNPs in each concentration appear in yellowish-brown color. Morover, all AgNPs were characterized by UV-Visible spectrophotometer, Particles Size Analyzer, Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and X-Ray Diffraction (XRD). Uv-Visible spectra of AgNPs were 429 nm, 429 nm, and 427 nm, respectively. Particle size was performed using Dynamic Light Scattering, they were 32.27 nm, 48.82 nm, and 52.33 nm, respectively. Additional, the potential conductivity of each sample was 0.193 mS/cm, 0.125 mS/cm, 0.135 mS/cm. The peaks of the diffraction pattern of silver nanoparticles clearly demonstrated in 2-theta value is 38.199. The morphology of the AgNPs was observed by SEM and TEM. X-ray diffraction confirmed the crystallinity of the AgNPs in cubic form based RC 03-065-2871.The antibacterial effect of the bioreducted AgNPs from TC leaf extract was done using Disc Diffusion Method showed that AgNPs has antibacterial ability better for gram negative bacteria than gram positive bacteria. This new biomimetic approach using TC leaf extract as reducing agents to synthesize biocompatible antibacterial AgNPs could easily be scaled up for additional food safety indicators applications.
Keyword: Biosynthesis, Microbial activity, Polyvinyl alcohol, Silver nanoparticles, Terminalia catappa

Judul: Green Synthesis Nanopartikel Perak Menggunakan Limbah Jeruk Purut (Citrus hystrix dc) dengan Variasi Konsentrasi AgNO3
Abstrak: Jeruk purut (Citrus hystrix) merupakan tumbuhan perdu yang kaya manfaat. Kandungan dalam kulit jeruk purut berpotensi dijadikan bahan bioreduktor dalam sintesis nanopartikel. Nanopartikel dengan sifat fisis dan kimiawinya yang unik diharapkan mampu meningkatkan nilai jual serta efektivitas pemanfaatannya. Nanopartikel perak sebagai salah satu jenis nanopartikel logam secara alami memiliki kemampuan antibakteri yang baik serta proses sintesisnya sudah banyak dilakukan. Pada penelitian ini, kulit jeruk purut dipilih sebagai bioreduktor dengan meninjau kondisi optimal pengaruh variasi konsentrasi AgNO3 dan waktu penyimpanan terhadap green synthesis nanopartikel perak. Rancangan percobaan dibuat menggunakan Response Surface Methodology dengan bentuk Central Composite Design. Ukuran partikel yang dihasilkan berkisar pada 86-236 nm yang masih dalam ukuran toleransi nanopartikel. Nilai absorbansi maksimum 0,241-0,506 yang tercapai pada panjang gelombang 268-279 nm. Hasil penelitian ini menunjukkan bahwa nanopartikel perak berdiameter kurang dari 100 nm tercapai pada variasi konsentrasi 1 mM dengan waktu simpan 1 dan 29 jam., Kaffir lime (Citrus hystrix) is a herbaceous plant that is rich in benefits. The content in kaffir lime peel has the potential to be used as a bioreductant in the synthesis of nanoparticles. Nanoparticles with unique physical and chemical properties are expected to increase the selling value and effectiveness of their utilization. Silver nanoparticles as a type of metal nanoparticles naturally have good antibacterial abilities and many synthesis processes have been carried out. In this study, kaffir lime peel was chosen as a bioreductant by reviewing the optimal conditions for the effect of variations in AgNO3 concentration and storage time on the green synthesis of silver nanoparticles. The experimental design was made using the Response Surface Methodology in the form of a Central Composite Design. The resulting particle size ranges from 86-236 nm which is still within the tolerance of nanoparticles. The maximum absorbance value of 0.241-0.506 is achieved at a wavelength of 267-279 nm. The results of this study showed that silver nanoparticles with a diameter of less than 100 nm were achieved at a concentration variation of 1 mM with a shelf life of 1 and 29 hours.
Keyword: AgNO3, Kulit jeruk purut, Nanopartikel, RSM, Sintesis hijau

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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