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 Rubberwood Glulam (Hevea brasiliensis Muell. Arg) Impregnated with Polystyrene to Subterranean Termites in Field Test
Abstrak: Kayu karet (Hevea brasiliensis Muell. Arg) ini termasuk ke dalam kelas awet V dimana rentan terhadap serangan organisme perusak kayu, sehingga ketahanannya perlu untuk ditingkatkan. Penelitian ini bertujuan untuk menganalisis pengaruh perlakuan impregnasi polistirena pada ketahanan glulam karet terhadap serangan rayap tanah setelah pengujian lapangan (field test) selama 4 bulan. Karakteristik glulam polistiren memiliki nilai rata-rata polymer loading sebesar 6,89%, kerapatan 0,71 g cm-3 dan kadar air 14,07%. Setelah dilakukan uji lapang, solid karet, glulam kontrol dan glulam polistiren masing-masing memiliki rata-rata nilai kehilangan berat sebesar 20,14%; 24,38%; dan 24,02% dengan rata-rata nilai ketahanannya terhadap rayap tanah sebesar 7,33; 7,33; dan 7,00. Hasil tersebut menunjukkan bahwa teknik glulam dan impregnasi polistirena yang diterapkan kurang efektif untuk meningkatkan ketahanan kayu awal (solid) terhadap serangan rayap tanah. Hal ini disebabkan karena nilai polymer loading yang kecil, sehingga perlu ditingkatkan agar ketahanannya juga dapat meningkat., Rubberwood (Hevea brasiliensis Muell. Arg) resistance is categorized as class V, susceptible to be attacked by destructive organisms. However, this resistance property can be improved through several actions. This study aims to analyze the effect of polystyrene impregnation on rubberwood glulam resistance to subterranean termites attack after field tests for 4 months. The polystyrene glulam had an average polymer loading of 6,89%, density of 0,71 g cm-3 and moisture content of 14,07%. After field testing, solid rubber, control glulam and polystyrene glulam each had an average weight loss value of 20,14%, 24,38% and 24,02% with an average of resistance to subterranean termites value of 7,33, 7,33 and 7,00. These results indicate that the polystyrene glulam technique has a less effective effect on increasing the resistance of solid wood to subterranean termites. This was due to the low polymer loading, which was important to be optimized in order to increase the wood resistance.
Keyword: glulam, impregnation, polystyrene, rubberwood, 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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