Judul: Perilaku Harian dan Jenis Pakan Presbytis sumatrana di Area Tambang Emas Martabe, Tapanuli Selatan, Sumatra Utara
Abstrak: Presbytis sumatrana (cek-cek) merupakan primata endemik dari Sumatera Utara dan tergolong terancam punah (endangered). P. sumatrana termasuk pemakan daun (folivore) namun juga memakan biji dan buah. Sampai saat ini belum ada penelitian mengenai P. sumatrana. Oleh karena itu, penelitian terkait perilaku harian dan jenis pakan sangat penting untuk dilakukan. Pengambilan data menggunakan metode scan sampling. Hasil penelitian menunjukkan perilaku istirahat, bergerak, dan makan sebagai tiga perilaku utama P. sumatrana. Perilaku-perilaku ini berbeda nyata (p < 0,05) pada setiap waktu pengamatan. Jenis kelamin tidak memengaruhi perilaku istirahat dan pakan antropogenik sedangkan strata usia tidak berpengaruh hanya pada perilaku pakan antropogenik. Meskipun banyak memakan buah Artocarpus elasticus (Terap), P. sumatrana juga mengonsumsi nasi sisa manusia. Perilaku P. sumatrana ini harus menjadi perhatian pihak manajemen perusahaan, agar akses mereka ke area tempat sampah dapat dibatasi, sehingga kawasan konservasi yang ada di area tambang dapat terjaga kealamiannya., Presbytis sumatrana (local: cek-cek) is an endemic primate from North Sumatra, classified as endangered. This folivorous primate also consumes seeds and fruits. To date, no research has been conducted on P. sumatrana, making studies on its daily behaviour and diet critically important. Behavioural observations were carried out using the scan sampling. The diet was concurrently documented. Three primary behaviours were noted: resting, moving, and eating. Significant behavioural variations (p < 0.05) were observed across different times. While significant differences were found in most behaviours when stratified by gender, no such differences were noted in resting behaviour and anthropogenic feeding. Anthropogenic feed is also not affected by age. Although the natural diet predominantly included the fruit of Artocarpus elasticus (Terap), rice being the most consumed anthropogenic food. The primate's consumption of human food waste is concerning; thus, it is recommended that company management restricts their access to waste areas to preserve the natural conservation area within the mining site.
Keyword: Cek-cek, daily feeding behaviour, leaf-eater monkey, Sumatra's endemic primates

Judul: Potential and Feed Preferences for Sumatran Orangutans at the Gunung Leuser National Park
Abstrak: Orangutan sumatera (Pongo abelii, Lesson 1827 ) adalah salah satu spesies primata yang keberadaannya di dunia terancam punah, sehingga perlu upaya melestarikannya melalui pengelolaan tumbuhan pakannya di dalam habitatnya. Penelitian dilaksanakan di Stasiun Penelitian Ketambe (SPK) dan Kawasan ekowisata Lawe Gurah (KELG) dengan tujuan menduga dan mengidentifikasi jenis pakan, ketersediaan pakan dan preferensi pakan orangutan sumatera. Pakan orangutan dikategorikan menjadi sangat disukai, disukai, kurang disukai, dan tidak disukai menggunakan Indeks Preferensi Jacobs (Di). Terindentifikasi spesies pohon pakan yang termasuk dalam 31 spesies dari 15 famili di SPK dan 41 spesies yang tergolong kedalam 28 famili di KELG. Jenis pakan yang sangat disukai adalah Rambung (Ficus sp.) berupa buah, daun muda dan bunga (Di=0,86), durian (Durio zibhetinus) berupa buah dan daun muda (Di=0,63). Perilaku makan orangutan sumatera, berdasarkan aktivitas makan terlihat aktivitas makan sebesar 38,34% dari aktivitas hariannya, buah adalah pilihan yang sangat disukai dengan persentase 78,17%. Preferensial pakan juga berpengaruh terhadap proporsi makan dari orangutan dimana proporsi remaja jantan lebih proporsional daripada orangutan dewasa jantan dengan persentase 25% berbanding 16%., The Sumatran orangutan (Pongo abelii, Lesson 1827 ) is one of the primate species whose existence in the world is threatened with extinction, so efforts are needed to preserve it through the management of its forage plants in its habitat. The research was carried out at the Ketambe Research Station (SPK) and the Lawe Gurah Ecotourism Area (KELG) with the aim of predicting and identifying the type of feed, the availability of feed and the food preferences of the Sumatran orangutan. Orangutan feeds were categorized into highly favored, preferred, less preferred, and disliked using the Jacobs Preference Index (Di). The forage tree species were identified as belonging to 31 species from 15 families in SPK and 41 species belonging to 28 families in KELG. The type of feed that was highly preferred was Rambung (Ficus sp.) in the form of fruit, young leaves and flowers with (Di=0.86), durian (Durio zibhetinus) in the form of fruit and young leaves with (Di=0.63). The eating behavior of Sumatran orangutans, based on eating activities, it can be seen that eating activity is 38.34% of their daily activities, fruit is the most preferred choice with a percentage of 78.17%. Feed preference also affects the proportion of eating from orangutans where the proportion of male juveniles is more proportional than adult male orangutans with a percentage of 25% versus 16%.
Keyword: Ficus sp, Jacob's preference index, Lawe gurah ecotourism area, Pongo abelii lesson 1827, Feed preference, Ketambe research station

Judul: Hamiltonian formulation for linear waves motion in two layers fluid
Abstrak: The surface wave could be considered as a wave that separates two fluids, namely water and air. Based on this assumption, it is introduced the interfacial wave, a wave between two layers of fluid with different density. The formulation of interfacial waves motion begins with deriving the base equation of irrotational ideal fluid. Furthermore, according to irrotational fluid assumption, the base equation can be stated in velocity potential. In this derivation, the fluids domain is assumed to be restricted by rigid lid boundary conditions, both at the upper and lower limit. Therefore, the interfacial waves motion can be explained in a hamiltonian formulation. In the hamiltonian formulation, total energy is defined as the sum of kinetic and potential energy. The hamiltonian system is obtained from reduction of kinetic energy by using the Dirichlet Neumann Operator. The resulted kinetic energy equation is nonlinear. Therefore, this form is linearized by first part of the Taylor expansion. This linearization gives a dispersion relation of linear wave. Based on this dispersion relation, the phase speed of the linear wave depends on the density ratio of the two layers fluid.
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