Judul: Growth Analysis of Sengon Buto (Enterolobium cyclocarpum G.) Revegetation Results at PT Bukit Asam Tbk, South Sumatera
Abstrak: Batu bara merupakan salah satu sumber energi alternatif yang telah lama digunakan sebagai pengganti hidrokarbon seperti minyak bumi. Penambangan batu bara yang dilakukan dapat menyebabkan degradasi lahan yaitu penurunan kualitas dari lahan tersebut. Tujuan penelitian ini adalah menganalisis pertumbuhan sengon buto di lahan hasil revegetasi tambang batu bara PT Bukit Asam Tbk. Data penelitian diambil dengan cara membuat 3 plot berukuran 25 m × 40 m dengan metode penentuan plot systematic sampling with random start pada setiap tahun tanam (2011, 2013, dan 2015). Intensitas sampling yang digunakan sebesar 10% pada lahan revegetasi seluas 3 ha. Hasil penelitian menunjukkan revegetasi yang dilakukan oleh PT Bukit Asam Tbk dinyatakan berhasil karena memiliki persentase hidup yang tinggi (>90%). Tahun tanam dan jarak tanam sangat berpengaruh nyata terhadap pertumbuhan tinggi total, tinggi bebas cabang, diameter batang, dan live crown ratio. Semakin tua umur tanam dan semakin lebar jarak tanam, maka semakin tinggi nilai tinggi total, tinggi bebas cabang, dan diameter batang; namun semakin rendah nilai live crown ratio., Coal is one alternative energy source that has long been used as a substitute for hydrocarbons such as petroleum. Coal mining carried out can cause land degradation, namely a decrease in the quality of the land. The purpose of this study was to analyze the growth of sengon buto in revegetated land of PT Bukit Asam Tbk. The research data was taken by making 3 plots measuring 25 m × 40 m with a systematic plot sampling method with random start in each planting year (2011, 2013, and 2015). The sampling intensity used was 10% on 3 ha of revegetated land. The results showed that the revegetation carried out by PT Bukit Asam Tbk was declared successful because it had a high percentage of life (>90%). Planting year and spacing have a significant effect on total height growth, branch-free height, trunk diameter, and live crown ratio. The older the planting age and the wider the planting distance, the higher the total height value, branch-free height, and trunk diameter; But the lower the value of the Live Crown Ratio.
Keyword: coal, branch free height, live crown ratio, trunk diameter, tree height

Judul: Evaluation of the Growth of Kayu Putih (Melaleuca cajuputi) Reclamation Results on PT Bukit Asam Post-mining Land, South Sumatera
Abstrak: Penambangan batu bara dengan metode open pit mining menyebabkan gangguan terhadap lingkungan sehingga reklamasi dan revegetasi perlu dilakukan. Revegetasi di PT Bukit Asam dilakukan dengan menggunakan tanaman lokal jenis kayu putih yang ditanam tahun 2016 – 2021. Tujuan penelitian yaitu mengevaluasi pertumbuhan kayu putih pada tahun tanam 2016 – 2021 serta menentukan status keberhasilan reklamasi berdasarkan daya hidup dan tutupan tajuk di lahan pascatambang PT Bukit Asam. Metode pengumpulan data pertumbuhan tegakan kayu putih dilakukan dengan purposive sampling pada petak ukur berukuran 40 m x 25 m. Intensitas sampling yang digunakan sebesar 5% dari lahan pascatambang kayu putih seluas 24 ha. Hasil penelitian menunjukkan bahwa tinggi, diameter batang, tebal tajuk, diameter tajuk, dan luas tajuk kayu putih pada tahun tanam 2016 memiliki pertumbuhan paling besar, sedangkan pada tahun tanam 2021 memiliki pertumbuhan paling rendah. Reklamasi lahan pascatambang pada tahap revegetasi telah mencapai nilai persentase hidup kayu putih > 80%, tetapi pada tahap penyelesaian akhir reklamasi belum berhasil dilakukan karena persentase tutupan tajuk kayu putih < 80%., Coal mining using the open pit mining method causes environmental disturbances, so reclamation and revegetation need to be carried out. At PT Bukit Asam, revegetation is carried out using local tree species, specifically kayu putih, planted between 2016 – 2021. The research aims to evaluate the growth of kayu putih during the period from 2016 – 2021 and determine the success status of reclamation based on tree survival rate and canopy cover in PT Bukit Asam’s post-mining land. Data collection for kayu putih tree growth was conducted using purposive sampling in sample plots measuring 40 m x 25 m. A sampling intensity of 5% was applied to the 24 ha post-mining reclamation area for kayu putih. Research results indicate that tree height, stem diameter, canopy thickness, canopy diameter, and canopy area of kayu putih showed the highest growth in the 2016 planting year, while the lowest growth occurred in the 2021 planting year. Although reclamation of post-mining land during the revegetation phase has achieved a survival rate of kayu putih > 80%, the final completion stage of reclamation has not been successful due to a canopy cover percentage < 80%.
Keyword: Canopy cover, Post-mining land, Survival rate, Tree growth

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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