Judul: Analysis of predator-prey model of holling-tanner type II with prey refuge and the harvesting population
Abstrak: Dalam tulisan ini dipelajari model mangsa-pemangsa Holling-Tanner tipe II dengan menambahkan spesies mangsa yang terlindung dan pemanenan spesies mangsa dan pemangsa yang dikembangkan oleh Das et al. (2013). Dari model ini, diperoleh tiga titik tetap. Kestabilan titik tetap pertama dapat bersifat sadel atau simpul takstabil, sedangkan titik tetap kedua bersifat sadel. Titik tetap ketiga dapat bersifat spiral takstabil, spiral stabil, atau simpul stabil bergantung nilai parameter mangsa yang terlindung dan pemanenan populasi. Bifurkasi Hopf terjadi pada titik tetap ketiga. Semakin kecil mangsa yang terlindungi mengakibatkan populasi pemangsa meningkat tidak stabil dengan solusinya limit cycle. Sebaliknya, semakin tinggi mangsa yang terlindungi mengakibatkan populasi mangsa dan pemangsa menuju stabil dengan pemangsa cukup kecil. Hal ini terjadi pula pada dinamika populasi akibat usaha pemanenan mangsa. Sedangkan pada usaha pemanenan pemangsa, semakin kecil pemanenan pemangsa mengakibatkan populasi pemangsa meningkat tidak stabil dengan solusinya limit cycle. Semakin tinggi pemanenan pemangsa mengakibatkan populasi pemangsa menuju kepunahan dan populasi mangsa meningkat stabil., This paper studied a mathematical predator-prey model of Holling-Tanner type II incorporating prey refuge and harvesting to both prey and predator species that was previously investigated by Das et al. (2013). This model provides three fixed points, where depending on the parameters values, stability of the first fixed point can be a saddle or unstable node, that of the second always be a saddle, and the third fixed point could be an unstable spiral, stable spiral or node depending on two parameters of protected prey and harvesting populations. Hopf bifurcation occurs on the third fixed point, where a decrease on the size of protected prey can affect the predator populations to be unstable and its solution approaching a limit cycle. Otherwise, an increase on the size of protected prey can affect the prey and predator populations to be stable with a fairly small predators. The same situation occurs also in the population dynamics when a harvesting effort is incurred on prey population. Whereas a decrease on the harvested predator population can result to an unstable growth of predator population with the existence of a limit cycle. In the opposite direction, the predator will be extinct and the prey grows steadily. Keywords: Hopf bifurcation, Holling-Tanner type II, prey refuge, harvesting populations, predator-prey
Keyword: bifurkasi Hopf, Holling-Tanner tipe II, mangsa yang terlindung, pemanenan populasi, mangsa-pemangsa

Judul: Bifurkasi Hopf pada Model Mangsa-Pemangsa Holling-Tanner Tipe II
Abstrak: In this paper a mathematical prey-predator model of Holling-Tanner type II and the existence of Hopf bifurcation were studied. In this model, three fixed points are obtained, in which one of them is a saddle point. The prey-predator population dynamics was simulated based on four cases, by increasing the interaction value of prey and predator. In the third case, the stable spiral changed into an unstable spiral and also observed the presence of limit cycles. This is known as Hopf bifurcation. Furthermore, for the fourth case both populations were almost extincted due to the increase of the interaction rate. Generally, it can be concluded that increasing the value of prey and predator interaction rate would change the stability of population. The prey-predator population will be stable when the prey and predator interaction rate is low, whereas the higher interaction rate would cause the extinction of both prey and predator populations
Keyword: prey-predator., limit cycle, Holling-Tanner type II, Hopf bifurcation

Judul: Pembuatan papan semen dari sabut kelapa, Cocos nucifera L.
Abstrak: Di Indonesia, terutama di daerah sentra kelapa, tempurung dan sabut hanya digunakan sebagai bahan bakar, bahan kerajinan, dan sebagian kecil diolah menjadi arang. Menurut penelitian sebelumnya (Masri 1998), sabut kelapa memiliki potensi untuk digunakan sebagai bahan dasar papan semen, meskipun papan yang dihasilkan pada penelitian ini belum dapat memenuhi standar JIS A 5417 – 1992, terutama pada sifat mekanisnya. Penelitian ini bertujuan untuk mempelajari pengaruh penggunaan serat sabut kelapa sebagai bahan baku papan semen, serta pengaruh peningkatan taraf semen dan penambahan accelerator CaCl2 terhadap kualitas papan semen.
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