Judul: Food Preferences of Bornean Orangutan in Lamandau Wildlife Sanctuary, Central Kalimantan
Abstrak: Orangutan kalimantan (Pongo pygmaeus wurmbii) termasuk salah satu spesies primata yang paling terancam kepunahan di dunia. Pakan orangutan sangat bervariasi tergantung habitatnya. Penelitian dilaksanakan di Suaka Margasatwa Lamandau untuk menduga ketersediaan pakan, mengidentifikasi jenis pakan, serta menduga preferensi pakan orangutan kalimantan. Penelitian dilakukan pada bulan Februari-Maret 2020, dengan mengikuti 5 individu orangutan selama 195 jam oleh 2 pengamat. Pakan orangutan dikategorikan menjadi sangat disukai, disukai, kurang disukai, dan tidak disukai menggunakan indeks preferensi Jacobs (Di). Berdasarkan analisis vegetasi, ketersediaan pohon pakan orangutan masih cukup baik. Terdapat 33 jenis pohon pakan yang termasuk dalam 18 famili. Selain itu, orangutan juga mengonsumsi serangga, liana, jamur, herba, tanah, dan pakan tambahan yang diberikan oleh pengelola. Buah merupakan bagian yang disukai (73,3%). Jenis pakan yang sangat disukai yaitu, katikal (Ochanostachys amentacea, buah, Di 0,95), gandis (Garcinia parvifolia, buah Di 0,83), kekupui (Sarcotheca diversifolia, daun muda, Di 0,78), dan malukan (buah, Di 0,56)., The Bornean orangutan (Pongo pygmaeus wurmbii) is one of the world's most endangered primates. Orangutan food is highly varied, depending on its habitat. This research was conducted in Lamandau Wildlife Sanctuary to estimate the food trees availability, identify Bornean orangutan food trees, and estimate their food preferences. The research was conducted on February-March 2020 by following five orangutans for 195 hours by two observers. By using the Jacobs preference index (Di), food is categorized as highly preferred, preferred, less preferred, and not preferred. Based on the vegetation analysis, the availability of orangutan food trees is still quite good. There were 33 tree species (18 families) of orangutan food consumed. However, orangutans also consumed insects, lianas, mushrooms, herbs, soil, and some additional food provided by the Wildlife Sanctuary Manager. Fruits were the preferred part eaten by orangutans (73,3%). Highly preferred food were ‘katikal’ (Ochanostachys amentacea; fruit, Di 0,95), ‘gandis’ (Garcinia parvifolia; fruit, D 0,83), ‘kekupui’ (Sarcotheca diversifolia; young leaves, Di 0,78), and ‘malukan’ (fruit, Di 0,56).
Keyword: Jacob’s preference index, Lamandau Wildlife Sanctuary, Ochanostachys amentacea, Pongo pygmaeus wurmbii, Preferred food

Judul: Behavior and Food of Reintroduced Bornean Orangutan (Pongo pygmaeus wurmbii) at Feeding Site and Forest Area in Lamandau Wildlife Sanctuary
Abstrak: Orangutan Kalimantan (Pongo pygameus wurmbii) adalah primata besar Asia berstatus ‘Dalam Bahaya Kritis’. Reintroduksi dilakukan untuk menekan penurunan populasi mereka di alam. Penelitian yang dilaksanakan pada bulan Februari-April 2021 di Suaka Margasatwa Lamandau bertujuan mengidentifikasi perbedaan perilaku di feeding site dan hutan alam, komposisi dan preferensi pakan tambahan dan alami orangutan kalimantan reintroduksi. Sebanyak empat kategori dari enam individu berbeda telah teramati selama 219 jam. Kedatangan orangutan ke feeding site secara nyata (P = 1 > α = 0,05) tidak dipengaruhi oleh pemberian pakan tambahan, sehingga aktivitas harian di hutan alamlebih besar. Aktvitas harian tertinggi yang dilakukan berturut-turut adalah makan, istirahat, dan berpindah. Komposisi pakan tambahan yang diberikan dalam bentuk buah berupa pisang (Musa spp.) dan pepaya (Carica papaya). Komposisi pakan alami tertinggi orangutan dari jenis-jenis tumbuhan adalah buah (51%), daun muda 25%, dan bagian tumbuhan lainnya (15%). Jenis pakan yang termasuk kategori sangat disukai adalah papung (Sandoricum emarginatum) sebesar 0,73, dan kumpang darah (Knema conferta) sebesar 0,66. Kategori lainnya yaitu sembilan jenis tumbuhan ‘Disukai’, tujuh jenis tumbuhan ‘Kurang Disukai’, 16 jenis tumbuhan ‘Tidak Disukai’, dan delapan jenis tumbuhan ‘Tidak Dikategorikan’., The Bornean orangutan (Pongo pygameus wurmbii) is a 'Critically Endangered' large Asian primate. Reintroduction had been implementing to suppress their population decline in the wild. The research was conducted in February-April 2021 at Lamandau Nature Sanctuary, aimed to identify differences in behaviour at the feeding site and natural forest, composition and preferences for additional and nature feed for Bornean orangutan reintroduced. A total of six different individuals with four categories had observed for 219 hours. The arrival of orangutans to the feeding site significantly (P = 1 > = 0,05) was not affected by additional feeding, so daily activities in natural forestswere longer. The highest daily activities performed consecutively were eating, resting, and moving. The composition of the supplementary feed had given in the form of fruit in the form of banana (Musa spp.) and papaya (Carica papaya). The highest composition of natural food for orangutans from plant species is fruit (51%), young leaves 25%, and other plant parts (15%). Types of feed which included in the category of 'Highly Favoured' were papung (Sandoricum ermarginatum) of 0,73 and kumpang darah (Knema conferta) of 0,66. Other categories are nine plant species 'Preferred', seven plant species 'Less Like', 16 plant species 'Disliked', and eight plant species 'Not Categorized'.
Keyword: Bornean orangutan, daily activities, feed preferences, feeding site, Lamandau nature sanctuary, reintroduction

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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