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: The Influence of Activated Charcoal Incorporation on Physicochemical and Antibacterial Properties of Chitosan/Aloe Vera Composite Films
Abstrak: Edible film kitosan potensial sebagai pengemas makanan dengan sifat antibakteri alami yang aman dan ramah lingkungan. Film kitosan murni sensitif terhadap kelembapan. Gel lidah buaya dan arang aktif dari limbah ampas kopi dimanfaatkan untuk perbaikan sifat film. Penelitian bertujuan mengetahui pengaruh penambahan arang aktif terhadap sifat fisikokimia dan antibakteri film komposit kitosan/lidah buaya. Metode sintesis film yaitu solution casting. Film dievalusi dengan Fourier Transform Infra Red FTIR dan Field Emission Scanning Electron Microscopy FESEM, uji sifat mekanis, Water Vapour Transmission Rate WVTR, kelarutan dalam air, biodegradasi, dan antibakteri. Penambahan arang aktif menurunkan nilai WVTR dan kelarutan film dalam air. Nilai WVTR 2,1 g/m2.jam-2,6 g/m2.jam. Nilai kelarutan dalam air 8,563%-34,981%. Waktu biodegradasi sempurna yaitu 7-17 hari. Penambahan arang aktif meningkatkan kemampuan antibakteri film kitosan, sedangkan sifat mekanis film menurun. Morfologi permukaan film yang kasar dan berpori akibat penambahan arang aktif. Gugus fungsi yang terkandung adalah O-H, N-H, C-H, dan C=O dari kitosan, C-O-C sakarida kitosan/lidah buaya, serta Si-O-Si khas arang aktif/silika, Chitosan edible films have the potential to be used as food packaging since their natural antibacterial properties, safe and environmentally friendly. Moisture is a problem for pure chitosan film. To enhance the film's properties, aloe vera gel and activated charcoal from coffee grounds were added. The aim of research was to determine the influence of activated charcoal on physicochemical and antibacterial properties of chitosan/aloe vera composite films. The film synthesis method is solution casting. The addition of activated charcoal decreased the WVTR value and the water-solubility of the film. The WVTR value 2.1 g/m2.hr-2.6 g/m2.hr and 8.563%-34.981% for water-solubility. The addition of activated charcoal increased the antibacterial capacity of the chitosan film, while the mechanical properties decreased. The complete degradability time for films is 7-17 days. The surface morphology of the film is rough and porous due to the addition of activated charcoal. The functional groups contained are O-H, N-H, C-H, C=O from chitosan, C-O-C chitosan/aloe vera saccharides, and Si-O-Si typically activated charcoal/silica
Keyword: activated charcoal, aloe vera, antibacterial, chitosan, edible film composite

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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