Judul: Analisis Metadata terhadap Struktur Populasi Orangutan Sumatra dan Ketersediaan Buah di Stasiun Penelitian Suaq Balimbing, Aceh Selatan, Indonesia
Abstrak: One factor that affects the distribution of orangutans in an area is fruit availability. When fruit availability is high, the energetic daily cost will be low because of the limited competition between individuals. This study aimed to observe how fruit availability affected the population structure of Sumatran Orangutans (Pongo abelii) in Suaq Balimbing. The observation was done with nest-to-nest and focal animal sampling observation methods, which analyzed using the Kruskal-Wallis test. Results show that many orangutans were spotted in the area during the years (2007-2019), with the highest number of 32 in 2010. The population structure dominancy spotted were unflanged males, mothers, juveniles, and flanged males, respectively. Adult males tend to move out from their birth area and have a comprehensive home range compared to mothers and/or females, which tend to have a small home range and stay in their birth area. Fruit availability has no significant effect on the presence of the individual of Sumatran orangutans in Suaq Balimbing. It might because Suaq Balimbing are known to have a very high fruit availability every year so that aggreration is common to happen with the orangutans.
Keyword: energetic cost, fruit availability, habitat productivity, Pongo abelii, population number

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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