Judul: Resistance of Polystyrene-Impregnated Mangium Wood  Glulam Against Subterranean Termite Attacks Through Laboratory Test
Abstrak: Glulam dari kayu cepat tumbuh seperti mangium masih memiliki sifat ketahanan yang rendah terhadap serangan organisme perusak. Penelitian ini bertujuan menganalisis ketahanan glulam kayu mangium (Acacia mangium Wild.) yang diimpregnasi polistirena terhadap serangan rayap tanah (Coptotermes curvignathus Holmgren) melalui uji laboratorium. Impregnasi stirena dilakukan dengan metode vakum-tekan dan menggunakan katalis kalium peroksodisulfat. Proses polimerisasi didasarkan pada pengovenan suhu 60 °C selama 24 jam. Glulam dibuat dari tiga lapis lamina yang dilabur perekat isosianat sebanyak 280 g/m2 menggunakan single spread. Sampel uji dibedakan menjadi solid mangium, glulam kontrol, dan glulam polistirena berukuran 1,6 x 5 x 80 cm3 (tebal x lebar x panjang). Karakteristik glulam polistirena memiliki nilai rata-rata weight percent gain sebesar 22,10%, kerapatan 0,75 g/cm3 , dan kadar air 11,25%. Pengujian ketahanan kayu terhadap rayap tanah melalui uji laboratorium berdasarkan SNI 7207-2014 menghasilkan nilai rata-rata penurunan bobot solid, glulam kontrol, dan glulam polistirena berturut-turut sebesar 15,53% termasuk kelas IV (tidak tahan), 8,30% termasuk kelas III (agak tahan), dan 6,18% termasuk kelas II (tahan). Teknik glulam polistirena cukup efektif meningkatkan ketahanan kayu awal (solid) terhadap serangan rayap tanah (Coptotermes curvignathus Holmgren)., Glulam from fast-growing woods such as mangium still has low resistance to attack by destructive organisms. This study aimed to analyze the glulam resistance of mangium (Acacia mangium Wild.) wood impregnated with polystyrene against subterranean termites (Coptotermes curvignathus Holmgren) through laboratory tests. Styrene impregnation was carried out by vacuum-press method and using potassium peroxodisulfate as catalyst. The polymerization process is based on an oven at 60 °C for 24 hours. Glulam is made from three layers of laminate which is coated with 280 g/m2 isocyanate adhesive using a single spread. The test samples were divided into solid mangium, control glulam, and polystyrene glulam measuring 1,6 x 5 x 80 cm3 (thickness x width x length). The characteristics of polystyrene glulam have an average weight percent gain of 22,10%, a density of 0,75 g/cm3, and a moisture content of 11,25%. Testing the resistance of wood to subterranean termites through laboratory tests based on SNI 7207-2014 resulted in the average weight loss of solid, control glulam, and polystyrene glulam, respectively, including class IV (not resistant), 8,30% including class III (slightly resistant), and 6,18% including class II (resistant). The polystyrene glulam technique is quite effective of increasing the resistance of the initial (solid) wood to subterranean termites (Coptotermes curvignathus Holmgren).
Keyword: Acacia mangium, Coptotermes curvignathus, glulam, polystyrene

Judul: Resistance of Mangium Wood Glulam (Acacia  mangium Willd.) Impregnated with Polystyrene against Subterranean Termites through  Graveyard Test
Abstrak: Glulam merupakan produk rekayasa alternatif yang ditujukan untuk memaksimalkan penggunaan kayu berdiameter kecil. Glulam berbahan baku kayu cepat tumbuh seperti mangium (Acacia mangium Willd.) perlu dimodifikasi untuk meningkatkan ketahanannya terhadap organisme perusak kayu. Impregnasi menggunakan polistirena dapat meningkatkan ketahanan kayu. Penelitian ini bertujuan menganalisis ketahanan glulam kayu mangium terimpregnasi polistirena terhadap rayap tanah melalui uji kubur selama 4 bulan. Impregnasi dilakukan dengan metode vakum tekan. Uji kubur dilaksanakan berdasarkan SNI 7207: 2014 dan ASTM D 1758-06.Glulam terimpregnasi polistirena memiliki nilai rata-rata polymer loading sebesar 5,25%, kadar air 13,83%, dan kerapatan 0,71 g/cm3. Setelah dilakukan uji kubur, nilai rata-rata kehilangan berat solid mangium, glulam kontrol, dan glulam polistirena berturut-turut sebesar 9,31%, 0,99%, dan 0,31%. Sementara itu, tingkat ketahanan berturut-turut sebesar 7,33; 7,33; dan 8,67. Secara keseluruhan, glulam polistirena memiliki ketahanan terhadap rayap tanah yang lebih baik dari kayu solid dan glulam kontrol., Glulam is an alternative engineering product aimed at maximizing the use of small-diameter wood. Glulam made from fast-growing wood such as mangium (Acacia mangium Willd.) needs to be modified to increase its biodeterioration resistance. The impregnation method using polystyrene can increase wood resistance. This study purposes to analyze the resistance of glulam mangium impregnated with polystyrene through the graveyard test for 4 months. The impregnation used the vacuum-pressed method. The graveyard test referred to SNI 7207:2014 and ASTM D 1758-06. Polystyrene glulam had average polymer loading of 5.25%, moisture content of 13.83%, and density of 0.71 g/cm3. After the graveyard test, the average weight loss of solid wood, glulam (untreated), and polystyrene glulam were 9,31%, 0,99%, and 0.31%. Meanwhile, the protection level were 7,33; 7,33; and 8.67. Overall polystyrene glulam had higher resistance against subterranean termites than solid wood and glulam (untreated).
Keyword: glulam, impregnation, mangium, polystyrene, wood resistance

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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