Judul: Pengaruh Waktu Tunda pada Model Siklus Bisnis Kaldor- Kalecki Menggunakan Fungsi Investasi Umum
Abstrak: Model dinamik dalam tulisan ini disusun dari model siklus bisnis Kaldor- Kalecki dengan mempertimbangkan adanya waktu tunda, yaitu waktu tunda antara keputusan berinvestasi dan implementasi. Analisis pertama dilakukan dengan mempertimbangkan adanya waktu tunda ketika kecenderungan untuk menabung relatif tinggi. Dari hasil analisis diperoleh satu titik tetap yang selalu stabil asimtotik untuk semua nilai waktu tunda. Analisis kedua dilakukan dengan mempertimbangkan adanya waktu tunda ketika kecenderungan untuk menabung relatif rendah. Dari hasil analisis tersebut, ditemukan nilai waktu tunda kritis yang menyebabkan sistem mengalami perubahan kestabilan, dari spiral stabil ke spiral takstabil. Pada waktu tundaan kritis ini, ditunjukkan adanya bifurkasi Hopf dan kemunculan limit cycle. Analisis selanjutnya dilakukan dengan mempertimbangkan model tanpa adanya waktu tunda. Dari hasil analisis diperoleh titik tetap yang stabil asimtotik untuk semua tingkat kecenderungan untuk menabung.
Keyword: bifurkasi Hopf, model Kaldor-Kalecki, siklus bisnis, waktu tunda

Judul: Solusi Model Siklus Bisnis Kaldor-Kalecki Tanpa Waktu Tunda Dengan Metode Runge-Kutta Orde Empat
Abstrak: Model siklus bisnis Kaldor-Kalecki adalah salah satu model siklus bisnis dalam bidang ekonomi. Model ini merupakan suatu siklus bisnis yang melibatkan pendapatan kotor dan stok modal yang dipengaruhi oleh fungsi tabungan dan fungsi investasi. Dalam tulisan ini disajikan model siklus bisnis Kaldor-Kalecki tanpa waktu tunda dengan dua tipe fungsi investasi, yaitu fungsi investasi yang merepresentasikan perilaku ekonomi global (fungsi investasi global) dan fungsi investasi yang merepresentasikan perilaku ekonomi lokal (fungsi investasi lokal). Dalam model ini dilakukan analisis kestabilan dan penyelesaian numerik menggunakan metode Runge-Kutta orde empat. Model dengan fungsi investasi global siklusnya lebih cepat stabil dibanding model dengan fungsi investasi lokal. Hal ini terjadi karena adanya pengaruh tingkat depresiasi stok modal. Semakin besar tingkat depresiasi stok modal maka laju stok modal akan mengalami penurunan sehingga menyebabkan peningkatan laju pendapatan kotor. Penyelesaian numerik ini memperlihatkan perbedaan perilaku antara model dengan fungsi investasi global dan model dengan fungsi investasi lokal.
Keyword: kriteria Routh-Hurwitz, metode Runge-Kutta orde empat, model siklus bisnis Kaldor-Kalecki

Judul: Phylogeography and Species Limits in the Papuan White Snake (Micropechis ikaheka) (Reptilia: Serpentes: Elapidae)
Abstrak: Papua white snake, Micropechis ikaheka, has been distingushed into two subspecies M.i. ikaheka and M.i. fasciatus. However, due to lack of data on their morphology, distribution and ecology, both subspecies often ignored in scintific discussions and refers only byas , Micropechis ikaheka. This study was designed to document the differences between M.i. ikaheka and M.i fasciatus by using scales characteristics and reproductive organ or hemipenes. The study also examine, zoogeography, habitat, diet and cannibalism of both subspecies to better understanding the the ecology of one of the most venomous snakes in the world. This study consists of three topics with method and also different in the size samples, respectively. The first study is the histology and microtopography of the skin were studied using paraffin method and Scanning Electron Microscope (SEM). The second is the hemipenis were examined by following Myers and Cadle (2003), and Zaher and Prudente (2003). The third is the abdominal surgery was carried out to document diet type and the investigate phenomenon of cannibalism in the snake. Specimens for this study came from the collection from Museum Zoologicum Bogoriense (MZB) and Universitas Negeri Papua’s Laboratory (LZU). The research result also indicated that the markers of skin and hemipenis described the same structure and microornamentation in all M. ikaheka groups being compared. Based specimens examined morphological descriptions do not s support the further differentiation in Micropechis. In short, two markers that used in this study could not sufficiently indicate the differences in the level of species and subspecies of M. ikaheka. The study, however, were able to delineate zoogeography and skin color patterns, which fall into four groups: M. i. ikaheka; M. i. fasciatus. M. i. ssp. “intermediate”; and M. i. ssp “black”. This study also revealed that color variations did not overlap in their geographic distribution. It is therefore, it suggested that environmental factors may contribute to the skin color variations. It also assumed that habitat discontinuous and biogeography factors may also cause the loss of the connection between the original populations (vicarians) or follow colonization events (dispersal). The examined of 22 stomach contents of M. ikaheka shows this species is carnivorous, and prey on vertebrates such as amphibians, fish, reptiles, and Mammals. These snakes are opportunistic predators since they prey on all that can be captured, but mainly reptiles (61.5%), followed by mammals and fish (both 15.4%), and amphibians (7.7%). Although categorized as terrestrial animal, the diet study showed that M. ikaheka snakes often go into the water to hunt for fish (the sample from Yapen island), including eel (the sample from Aru island). Based on prey items indentified, there is evidence that M. ikaheka is cannibal. At this time, there still no record on reason for cannibalism, but it is assumed that cannibalism was due to competition between populations and means to control population.
Keyword: geographic variation, white snake, papua