Judul: pH Analysis of Tapanuli Orangutan Diet
Abstrak: Tapanuli orangutans are the newest and most endangered great ape species that have been known. Meanwhile, the pH values of Tapanuli orangutan diet is not available. Therefore, the aim of this study is to analysis the pH values of Tapanuli orangutan diet. The study was conducted from February to April 2019 at Camp Mayang, Batang Toru Research Station, North Sumatera. Next, foraging activity data were collected using focal animal sampling method. The pH values of diet sample were measured by MColorpHastTM as universal indicator of pH. SPSS 16.0 software was used in data processing. Data analysis was done with Shapiro-Wilk for normality test, while Kruskal-Wallis and Mann-Whitney for significant diferences test. In this study, five Tapanuli orangutans, two adolescent female and three adult female, have been followed. Fruits are their dominant food types. Camnosperma auriculatum fruits are their dominant diet during the observation. There is no significant differences between adolescent and adult female Tapanuli orangutans in the numbers of diet items at each pH values. On one hand, Tapanuli orangutan diets have pH values range between 3-7. On the other hand, Bornean and Sumatran orangutans prefer to eat fruits with range of pH values between 4-5.
Keyword: diet, food types, foraging activity, pH values, Tapanuli orangutans

Judul: Activity  Budget and Diet in Sumatran Orangutan (Pongo abelii) at Soraya Research Station, Aceh
Abstrak: The Sumatran orangutan (Pongo abelii) is categorised as critically endangered by the International Union for Conservation of Nature (IUCN). Orangutan existence in nature is increasingly threatened due to poaching and high rates of habitat deforestation. Understanding the daily activities and foraging behaviour of orangutans and their relationship to food availability can provide information on how orangutans can adapt to environmental changes in their habitat . Soraya Research Station (SRS) is a research station located in The Leuser Ecosystem and is a natural habitat for the Sumatran orangutan. However, information regarding the relationship between food availability and its relation to the daily activities and diet of orangutans in this location has not been reported. This study aims to observe orangutans daily activities and diet composition in SRS and their relationship with food availability. We observed the activity budget and diet from October 2021 until March 2022 at the Soraya Research Station (SRS). SRS is located in Pasir Belo Village, Sultan Daulat District, Subulussalam City, Aceh Province (N 02o 55’414”-E97o55’731”). The daily activity and feeding behaviour observation was conducted used focal animal sampling methods and instantaneous method with an interval of two minute. All data collected followed the standard collection of orangutan data in the field. The collection of phenological data and the food availability was carried out using the existing phenological plots at the research station. The number of phenological plots observed every month was 20 plots with a plot size of 20 x 20 m (0.8 Ha), estimated to consist of 550 trees. The phenological phases observed included young leaves, flowers, fruit, and ripe fruit. The phenological data and annual fruit availibility from 2017-2022 were also analyzed. Later, our data were analysed at the Laboratory of Biosystematics and Animal Ecology, Department of Biology, IPB University. The results show that the FAI index at SRS were low, only reaching 1.01%. Daily activity observations were carried out on five individual Sumatran orangutans in SPS, consisting of one adult female, two flanged males, one unflanged male, and one juvenile male in total 648 hours observations. Resting is the activity with the highest percentage (48%), followed by foraging (22.5%) and moving (21.8%). Low fruit availability affects Sumatran orangutans in SPS to have a high percentage of resting activity. The high percentage of rest activity aims to limit their energy expenditure. Analysis of diet composition showed that Sumatran orangutans in SPS consumed the highest percentage of bark (40.6%), followed by fruits and other plants (28.9% and 15.6%, respectively). The high consumption of bark by orangutans can be a fallback food in SPS and is thought to be a form of adaptation when fruit is scarce. The uniqueness of the SRS’s ecology characteristic might not be suitable for orangutans to live. Nevertheless, SRS can be considered a connected forest between the primary forest (Leuser National Park) and the surrounding belt forest area and other used forest areas. It can be considered a natural habitat for the Sumatran orangutans to meet their daily roaming area. The study on daily activities, population and phenology in SRS needs to be continued.
Keyword: Orangutan sumatra, Aktivitas harian, Fenologi, FAI, Komposisi pakan, Adaptasi

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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