Judul: Structure and Composition of Vegetation in Post-Gold  Mining Land in South Tapanuli, North Sumatera
Abstrak: Metode tambang terbuka (open pit mining) pada tambang emas berdampak signifikan terhadap lingkungan. Penelitian ini bertujuan menganalisis struktur dan komposisi vegetasi pada area revegetasi lahan pascatambang emas di Tapanuli Selatan, Sumatera Utara. Analisis struktur dan komposisi vegetasi diamati pada usia revegetasi yang berbeda (2, 3, 7, 8, 9, 10 tahun dan hutan alam sebagai pembanding). Pengambilan data area revegetasi dilakukan dengan metode kuadrat dan pengambilan data di hutan alam menggunakan metode garis berpetak. Sebanyak 22 famili yang tersebar di antara 37 jenis semai dan tumbuhan bawah, 19 jenis pancang, 14 jenis tiang, dan 7 jenis pohon ditemukan pada area revegetasi. Struktur tegakan pada area berusia 10, 9, dan 8 tahun, serta hutan alam memiliki bentuk kurva J terbalik. Hasil perhitungan indeks kekayaan jenis (R) dan indeks keragaman jenis (H') termasuk rendah hingga sedang, dan indeks kemerataan (E) termasuk rendah hingga tinggi. Tanah menunjukkan tekstur lempung hingga liat, dengan kategori pH asam hingga agak asam, dan kandungan bahan organik yang rendah. Seiring bertambahnya usia revegetasi, terjadi peningkatan kadar C-organik dan N-total pada tanah., The open-pit mining method in gold mines has significant impact on the environment. This study aimed to analyze the structure and composition of vegetation in revegetation area of post-gold mining land in South Tapanuli, North Sumatera. In this study, vegetation structure and composition analysis were observed in different revegetation years (2, 3, 7, 8, 9, 10 years and natural forest as control area). Data collection in revegetation areas and natural forests were studied using quadrat method and strip method, respectively. A total of 22 families distributed among 37 species of seedlings and undergrowth, 19 species of saplings, 14 species of poles, and 7 species of trees were found in revegetation areas. The stand structure in areas aged 10, 9, and 8 years, as well as in natural forests, has an inverted J-shaped curve. The species richness index (R) and species diversity index (H') were low to moderate categories, and the evenness index (E) was low to high. The soils exhibited a loam to clay textures, with a slightly acidic to acidic pH, and limited organic matter. It was discovered that total organic C and N levels increased with the age of revegetation.
Keyword: nilai penting, penambangan terbuka, podsolik merah kuning, reklamasi, important value, open-pit mining, red-yellow podzolic, reclamation

Judul: Vegetation and Environmental Characteristics in Land Ecosystems Results from Revegetation on Post-Coal Mining Lands PT. Pesona Khatulistiwa Nusantara
Abstrak: Pertambangan batu bara mengakibatkan hilangnya vegetasi yang berada di atas permukaan tanah, mengubah struktur, dan tekstur tanah. Kegiatan revegetasi dilakukan untuk memulihkan kembali kondisi lingkungan. Penelitian ini bertujuan untuk menganalisis karakteristik vegetasi dan lingkungan pada areal revegetasi lahan pascatambang batu bara. Metode penelitian menggunakan analisis vegetasi dan analisis biofisik lingkungan (edafis dan klimatis). Hasil penelitian menunjukkan bahwa hutan alam (ekosistem referensi) memiliki jenis vegetasi yang lebih banyak. Lahan revegetasi yang diamati hanya didominasi oleh satu jenis saja, yaitu sengon laut (Falcataria moluccana), sehingga nilai indeks keanekaragaman jenis, indeks kekayaan jenis, dan indeks kemerataan jenis hutan alam lebih tinggi daripada lahan revegetasi. Nilai indeks kesamaan tergolong tinggi hanya ditemukan pada lokasi lahan revegetasi umur 10 tahun dan 2 tahun pada tingkat pancang dan tiang. Lahan revegetasi umur 10 tahun memiliki total biomassa dan simpanan karbon lebih tinggi dibandingkan lahan revegetasi umur 2 tahun. Karakteristik kesuburan tanah lahan revegetasi umur 2 tahun memiliki nilai rendah daripada kedua lokasi lainnya, karena memiliki pH masam, C-organik sangat rendah, kapasitas tukar kation (KTK) rendah, dan kejenuhan basa (KB) yang sedang., Coal mining results in the loss of aboveground vegetation, changing the structure and texture of the soil. Revegetation activities are carried out to restore environmental conditions. This study aims to analyze the characteristics of vegetation and the environment in the revegetation area of post-coal mining land. The research method used vegetation analysis and biophysical analysis of the environment (edaphic and climatic). The results showed that natural forest (reference ecosystem) has more vegetation types. The revegetated land is only dominated by sengon laut (Falcataria moluccana), so the value of the species diversity index, species richness, and species evenness of natural forest is higher than the revegetated land. High similarity index values were only found in the second location of revegetated land at the sapling and pole levels. The 10-year-old revegetated land had higher total biomass and carbon storage than the 2-year-old revegetated land. Soil fertility characteristics of 2-year-old revegetated land have low values than the two locations, because they have acidic pH, very low C-organic, low cation exchange capacity (CEC), and medium base saturation.
Keyword: coal, post-mining, revegetation, soil, vegetation

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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