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: Analysis of Vegetation Development and Soil Properties In Post-Mining Land Revegetation Area at PT Tambang Tondano Nusajaya, North Sulawesi
Abstrak: Kegiatan revegetasi dapat membentuk struktur dan komposisi tegakan serta dapat meningkatkan kualitas tanah. Tujuan penelitian ini yaitu menganalisis perkembangan komposisi dan struktur vegetasi, menganalisis sifat fisik dan kimia tanah, dan menganalisis hubungan antara umur revegetasi dengan sifat-sifat tanah pada areal revegetasi lahan pascatambang. Metode pengambilan data vegetasi yaitu metode Systematic Sampling with Random Start dan metode jalur berpetak (transek), sedangkan untuk data tanah pengambilan contoh tanah secara komposit. Hasil secara keseluruhan terdapat 41 jenis vegetasi pokok, 7 jenis vegetasi sulaman, dan hadirnya 24 jenis alami. Lahan revegetasi umur 9 tahun memiliki rata-rata LBDS mendekati hutan alam yaitu sebesar 1,90 cm2. Hasil analisis struktur vegetasi menunjukkan areal revegetasi umur 3 – 10 tahun memiliki struktur vegetasi yang lengkap. Dari komposisi jenisnya, areal revegetasi yang memiliki jumlah jenis terbanyak yaitu areal revegetasi umur 7 tahun sebanyak 45 jenis. Hasil analisis sifat fisik dan kimia tanah menunjukkan kondisi yang beragam namun dominan telah mampu mendukung pertumbuhan vegetasi. Areal yang memiliki kondisi vegetasi dan karakteristik tanah mendekati hutan alam adalah areal revegetasi umur 10 tahun. Hasil analisis korelasi menunjukkan hubungan antara umur vegetasi dengan sifat tanah sangat lemah kecuali pada variabel C-Organik dan C/N rasio yang memiliki hubungan cukup kuat., Revegetation activities can shape the vegetation stands and can improve soil quality. This study aimed to analyze the development of vegetation composition and structure, analyze the physical and chemical properties of the soil, and analyze the relationship between revegetation age and soil properties. We use the Systematic Sampling method with Random Start and the transect method for collected vegetation data, while the soil sampling is composite. Overall, there are 41 basic species, 7 embroidered species, and 24 natural species. The 9-year-old revegetation land has an average basal area close to natural forest, which is 1,90 cm2. The vegetation structure shows that the revegetation area aged 3-10 years has a complete vegetation structure. The revegetation area aged 7 years has the highest number of species with 45 species. The results of the physical and chemical properties of the soil show that various but dominant conditions have been able to support the growth of vegetation. The 10-year-old revegetation area has vegetation conditions and soil characteristics close to a natural forest. The correlation analysis showed that the relationship between vegetation age and soil properties was very weak, except for the C-Organic variable and the C/N ratio which had a fairly strong relationship.
Keyword: C/N ratio, Organic-C, post gold mining, reclamation, revegetation

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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