Judul: Estimating the Stand Biomass of  Community Forest at the Taman Wijaya Rasa Cooperative (Kostajasa) Kebumen  District Using the Tree Sampling
Abstrak: Metode tree sampling belum pernah digunakan untuk menduga biomassa tegakan hutan rakyat, sehingga jumlah pohon contoh yang efisien untuk metode tree sampling belum diketahui. Penelitian ini bertujuan untuk menentukan jumlah pohon contoh yang efisien untuk menduga biomassa tegakan, cadangan karbon, dan serapan CO2 pada hutan rakyat Kostajasa. Penelitian ini mengukur 3, 4, 5, 6, 7, 8, 9, 10, 11, dan 12 pohon contoh yang paling dekat dengan pusat plot contoh dari 81 unit contoh yang tersebar di lapangan dengan metode stratified sampling. Data yang diambil pada setiap unit contoh adalah jenis pohon, diameter pohon, tinggi pohon, dan jarak pohon terjauh. Hasil penelitian menunjukkan bahwa 12 pohon contoh dapat digunakan untuk menduga biomassa tegakan, menghasilkan rata-rata biomassa sebesar 83,41 ton/ha atau total biomassa 27632,88 ton dengan sampling error 14,08%. Nilai tersebut setara dengan cadangan karbon sebesar 39,20 ton/ha dengan total 12987,45 ton atau serapan CO2 sebesar 143,87 ton/ha dengan total 47663,95 ton., The tree sampling method has never been used to estimate stand biomass of community forests, so that an efficient number of sample tree for the tree sampling method is not known yet. The study aimed to determine an efficient number of sample tree for estimating the stand biomass, carbon stock, and CO2 sequestration of the Kostajasa’s community forests. This study measured 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 sample trees closest to the center of 81 sample units, which were established in the field using a stratified sampling method. The data collected in each sample unit were tree species, tree diameter, tree height, and distance to the farthest tree. The results showed that 12 sample trees could be used to estimate the stand biomass, resulting a mean biomass of 83,41 ton/ha or a total biomass of 27632,88 tons with a sampling error of 14,08%. These values equal to the carbon stock of 39,20 ton/ha or 12987,45 tons in total or the CO2 sequestration of 143,87 ton/ha or 47663,95 tons in total.
Keyword: biomass, community forest, tree sampling

Judul: Estimating Stand Volume of the Community Forests at the Taman Wijaya Rasa Cooperative (Kostajasa) Kebumen Regency Using Plot Sampling
Abstrak: Metode inventarisasi hutan yang efisien diperlukan untuk mendukung pengelolaan hutan rakyat. Namun, masih sedikit penelitian tentang ukuran plot contoh lingkaran yang sesuai untuk memperkirakan volume tegakan hutan rakyat. Penelitian ini bertujuan menentukan ukuran plot contoh lingkaran yang optimal untuk menduga volume tegakan hutan rakyat Kostajasa. Pendugaan volume tegakan dilakukan dengan menggunakan 81 plot contoh dengan lima ukuran yaitu 0,01 ha, 0,02 ha, 0,03 ha, 0,04 ha, dan 0,05 ha yang ditempatkan di lapangan dengan menggunakan metode pengambilan contoh acak sederhana. Data yang diukur pada setiap plot contoh adalah jenis pohon, diameter setinggi dada, dan tinggi pohon. Hasil penelitian menunjukkan bahwa ukuran plot yang paling optimal untuk menduga volume tegakan di hutan rakyat adalah 0,05 ha dengan sampling error 9,24%., An efficient forest inventory method is required to support community forest management. However, there is still few studies on the appropriate size of a circular sample plot for estimating stand volume of community forests. This study aimed to determine an optimal size of the circular sample plot for estimating the stand volume of Kostajasa’s community forests. The stand volume estimation was carried out using 81 sample plots with five sizes, namely 0,01 ha, 0,02 ha, 0,03 ha, 0,04 ha, and 0,05 ha, which were established in the field using the simple random sampling method. The data measured in each sample plot were tree species, diameter at breast height, and tree height. This study showed that the most optimal plot size for estimating stand volume in community forests is 0,05 ha with a sampling error of 9,24%.
Keyword: community forest, sample plot, volume

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.
Keyword: