Judul: Antibacterial Activity of Membrane Chitosan-Polyvinyl  Alcohol Containing Green Grass Jelly and Moringa Leaves Extracts
Abstrak: Chitosan is a natural polymer that can be used as a wound dressing material. Chitosan has intrinsic properties, such as biocompatibility, non-toxic, hemostatic, biodegradable, and has antibacterial activity. However, chitosan has less elasticity and rigid properties. Therefore, chitosan needs to be combined with other materials in order to increase its elasticity, one of which is the addition of polyvinyl alcohol (PVA). Antibacterial properties of the composite needs to be enhanced. It can be done by adding leaves extracts with antibacterial activities such as green grass jelly leaf (Cyclea barbarta M.) and moringa leaves (Moringa oleifera L.). The antibacterial content of green grass jelly and moringa leaves can be developed as additional ingredients in making wound dressing membranes. The purpose of the research was to developed the chitosan-PVA membrane with the addition of green grass jelly leaf extract and moringa leaves to increase the antibacterial activity of the membranes that have potential as a wound dressing; and evaluate the membrane mechanical properties. Green grass jelly and moringa leaves were extracted with 96% ethanol by the maceration method. Green grass jelly and moringa leaf extracts were tested for phytochemical metabolites and antibacterial activities. The results of phytochemical testing of both extracts showed the presence of alkaloids, flavonoids, saponins, tannins, and phenols, while the triterpenoid test showed negative results. Combines green grass jelly and moringa leaf extracts in a ratio of 75:25, 50:50 and 25:75 were tested by disc diffusion methods against Staphylococcus aureus and Escherichia coli. The highest inhibition zone was produced by extracts with a ratio of 50:50 against S. aureus dan E. coli, 13,00 mm and 7,00 mm, respectively. The ratio of green grass jelly leaf extract and moringa leaf (50:50) with the highest antibacterial activity was added to chitosan-PVA membrane with a ratio of 5:5, 6:4 and 7:3. Each membrane was tested for antibacterial activity. Antibacterial activities in the membran of 7:3 with extracts had a larger area of inhibition against S. aureus dan E. coli compared to membrane without extract. The membrane's mechanical performance were performed for its density, tensile strength, elongation, and water vapor permeability. The density and water vapor permeability test results showed that the membrane with the addition of extract had better results compored to membrane without the addition of extract. Mechanically, adding extract decreased the tensile strength and elongation membrane, 80,20% elongation and 13,77 MPa tensile strength, but still included in the medical material standard, elongation value of 17-207% and tensile strength of 1-24 MPa. The membrane with best performance further analyzed with Fourier Transform Infra-Red (FTIR) and Scanning Electron Microscope (SEM). Characterization by FTIR showed chitosan-PVA membrane with extract the N-H group has a peak with two wave numbers at 1564 and 1554 cm-1 this is expressed as amide overlapping with amine and protonated amine, while the SEM characterization on the membrane with the addition of the extract was quite homogeneous because the distribution of the extract on the surface was quite even. The membrane with the addition of extract showed the best results, based on the antibacterial activity test results from the alloy membrane
Keyword: antibacterial, chitosan, mechanic, polyvinyl alcohol

Judul: Tambahan Kulit Batang Kelor (Moringa oleifera) sebagai Antibakteri pada Bioplastik Pati Onggok Singkong dan Kitosan
Abstrak: Antibakteri diperlukan pada bioplastik berbasis pati untuk memperpanjang daya simpan. Kulit batang kelor (Moringa oleifera) menjadi salah satu solusi sebagai bahan antibakteri karena kandungan metabolit sekunder, seperti fenolat dan tanin. Penelitian ini bertujuan mengukur kemampuan kulit batang kelor (Moringa oleifera) sebagai antibakteri pada bioplastik berbasis pati onggok singkong dan kitosan. Bioplastik dibuat tanpa ekstrak kulit batang kelor dan dengan ekstrak kulit batang kelor sebanyak 4, 8, dan 12 mL. Berdasarkan uji t terdapat perbedaan yang nyata antara bioplastik tanpa tambahan ekstrak dan dengan ekstrak etanol kulit batang kelor. Bioplastik yang ditambah 8 mL ekstrak dapat menghambat bakteri Staphylococcus aureus dengan diameter zona hambat tertinggi. Tambahan gliserol memengaruhi sifat mekanik bioplastik. Sifat kuat tarik menurun dan elongasi bioplastik meningkat jika tambahan gliserol semakin banyak. Daya serap air dan ketebalan bioplastik semakin meningkat saat ditambahkan gliserol. Ekstrak etanol kulit batang kelor memengaruhi elongasi bioplastik., Antibacterial is required in starch-based bioplastics to extend shelf life. Moringa bark (Moringa oleifera) is one of the solutions as antibacterial agents due to its secondary metabolites, such as phenolics and tannins. This experiment aims to determine the ability of Moringa bark as an antibacterial in bioplastics based on cassava starch and chitosan. Bioplastics were prepared without and with bark extract of 4, 8, and 12 mL. The t-test showed a significant difference between the bioplastics without and that with ethanol extract of Moringa bark. Bioplastics added with 8 mL extracts can inhibit Staphylococcus aureus with the highest inhibition zone diameter. The addition of glycerol affects the mechanical properties of the bioplastics. The tensile strength decreased, and the elongation of the bioplastic increased as the addition of glycerol increased. In addition, the water absorption and thickness of the bioplastics increased when glycerol was added. The ethanol extract of Moringa stem bark affects bioplastic elongation.
Keyword: antibacterial, bark of Moringa oleifera, bioplastics, cassava starch, chitosan

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: