Judul: Ekstraksi Silikon Dioksida dari Abu Jerami Padi.
Abstrak: Jerami padi merupakan salah satu limbah terbesar dari bagian tanaman padi, biasanya limbah jerami padi hanya dibakar saja setelah proses panen oleh petani, padahal jerami padi mengandung senyawa anorganik utama yaitu silikon dioksida sebesar 75%. Ekstraksi silikon dioksida salah satunya dipengaruhi oleh suhu pengabuan. Variasi suhu yang digunakan pada penelitian ini yaitu 700 °C, 800 °C dan 900 °C. Semua proses ekstraksi dengan 3 variasi suhu pengabuan ini sama mulai dari pembakaran jerami dengan korek api, pencucian menggunakan HCl 3% teknis dan pembilasan menggunakan aquades dengan suhu 105 °C. Proses yang berbeda adalah proses pengabuan dalam furnace dengan set up suhu yang berbeda. Silikon dioksida dengan suhu pengabuan 700 °C memiliki rentang nilai konduktivitas listrik dari frekuensi 50 Hz sampai 5 MHz berupa semikonduktor, silikon dioksida dengan suhu pengabuan 800 °C memiliki rentang nilai konduktivitas listrik dari frekuensi 10.245 kHz sampai 5 MHz berupa semikonduktor dan silikon dioksida dengan suhu pengabuan 900°C memiliki rentang nilai konduktivitas listrik dari frekuensi 11.502 kHz sampai 5 MHz berupa semikonduktor. Silikon dioksida dengan suhu pengabuan 700 °C, 800 °C dan 900 °C memiliki kemurnian berturut-turut yaitu 80.97% atom; 99.99% atom; 61.53% atom. Silikon dioksida dengan suhu pengabuan 700 °C, 800 °C dan 900 °C memilki derajat kristalinitas berturut-turut yaitu 25.819%, 44.24% dan 45.608%.
Keyword: extraction, ignition, purity, rice straw, silicon dioxide

Judul: Ekstrasi Silika dari Sekam Padi dengan Metode Pelarutan dan Pengendapan Silika serta Analisis EDX dan FTIR
Abstrak: Estimated amount of rice production in 2013 is 69.27 million tons. Compared to rice production in 2012 increased by 0.21 million tons. Some researchers have done the extraction of silica from rice husk through process using alkali solvent and acid precipitation of silica. The aim of this research is to extract silica using alkali solvent and to study the effects of alkali solvent toward the purity and the molecular structure of silica. The procedure of this research covers two phases namely carbonization and silica extraction of rice husk. The largest rendemen obtained is 22.59%, when 20% NaOH solution was added. The largest purity of silica (92.01%) were obtained when 20% KOH solution added with potasium and rubidium act as inpurities. FTIR spectra on 463-486 cm-1, 617 cm-1, 787-802 cm-1, and 1095-1103 cm-1 waves number show the presence of Si-O-Si (siloksan) group, as well as on 1643 cm-1 and 3448-3464 cm-1 waves number shows the existence of Si-OH (silanol) group or a molecule of water. The value of symmetry streching vibration spring constant Si-O is 948.891 – 1017.991 N/m
Keyword: Siloksan., Silica, Silanol, Rice husk, FTIR

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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