Judul: Natural food preference and Feeding Activity of Sumatran Elephant in Pusat Latihan Satwa Khusus Tangkahan, Sumatra Utara
Abstrak: Preferensi pakan adalah tingkat kesukaan satwa dalam memilih makanannya. Penelitian ini bertujuan untuk mengidentifikasi jenis tumbuhan pakan, preferensi pakan, dan aktivitas makan Gajah Sumatera di PLSK Tangkahan. Metode yang digunakan untuk identifikasi jenis tumbuhan pakan adalah analisis vegetasi, sedangkan untuk preferensi pakan dan aktivitas makan adalah focal animal sampling. Digunakan tiga ekor gajah sebagai objek penelitian. Hasil penelitian menunjukan 28 jenis tumbuhan yang menjadi pakan alami gajah. Preferensi pakan alami yang paling disukai gajah adalah rumput paitan (Axonopus compressus), bagian tumbuhan yang paling banyak dimakan adalah daun dan batang. Lama aktivitas makan gajah Olive sebesar 1.811 menit, Eropa 1.630 menit, dan Carlos 1.699 menit. Rata-rata aktivitas menarik pakan dengan belalai sebesar 737 menit, membersihkan pakan dengan belalai 340 menit, menginjak pakan dengan kaki 132 menit, dan memasukkan pakan kemulut 503 menit., Food preference is the level of animal preference in choosing its food. This study aims to identify the types of food plants, food preferences, and feeding activities of Sumatran elephants in Tangkahan PLSK. The method used to identify the type of food plants is vegetation analysis, while for food preferences and feeding activities is focal animal sampling. Three elephants were used as research objects. The results showed 28 types of plants that become natural food for elephants. The most preferred natural food preference of elephants is paitan grass (Axonopus compressus), the most eaten plant parts are leaves and stems. The duration of feeding activity of Olive elephants was 1,811 minutes, Eropa 1,630 minutes, and Carlos 1,699 minutes. The average activity of pulling food with the trunk was 737 minutes, cleaning food with the trunk 340 minutes, stepping on food with the feet 132 minutes, and putting food in the mouth 503 minutes.
Keyword: Preferensi Pakan, Aktivitas Makan

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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