Judul: Analysis of Species Composition and Stand  Structure of Degraded Natural Forests Before and After Gap Planting in IUPHHK- HA PT. Sarmiento Parakantja Timber
Abstrak: Rehabilitasi hutan alam terdegradasi dapat dilakukan dengan penerapan teknologi tanam rumpang. Komposisi jenis dan struktur tegakan menjadi salah satu indikator lingkungan untuk mengetahui keberhasilan penerapan teknologi tanam rumpang. Penelitian bertujuan untuk mengetahui pengaruh tanam rumpang terhadap komposisi jenis dan struktur tegakan penyusun hutan. Penelitian dilakukan pada bulan Maret sampai Mei 2021 dengan metode analisis vegetasi pada tegakan sebelum dan sesudah tanam rumpang. Hasil penelitian menunjukkan bahwa komposisi jenis tegakan hutan memiliki perbedaan antara sebelum dan sesudah tanam rumpang dengan penurunan nilai kerapatan pada seluruh tingkat vegetasi, namun nilai indeks keanekaragaman hayati sesudah tanam rumpang tidak berbeda dengan sebelum tanam rumpang dengan indeks kesamaan komunitas bernilai mendekati 100%. Struktur tegakan sebelum dan sesudah tanam rumpang untuk seluruh jenis pohon membentuk kurva “J” terbalik dengan persamaan eksponensial negatif nilai R2 mendekati 1 serta nilai p-value<0,05. Penerapan teknologi tanam rumpang menggunakan areal sebesar 41,97% dari total areal plot penelitian., Rehabilitation of degraded natural forests can be carried out by applying gap planting technology. Species composition and stand structure are one of the environmental indicators to determine the success of the application of gap planting technology. The research aim is to determine the impact of gap planting on the species composition and stand structure of the forests. The research was conducted from March to May 2021 by using vegetation analysis method on before and after gap planting stand. The results showed that the species composition of forest stand had differences between before and after gap planting with a decrease in density values at all vegetation levels, but the biodiversity values index after gap planting was not different from before gap planting and the community similarity index is close to 100%. The stand structure of all tree species before and after gap planting form the "J" reversed curve and a negative exponential equation with a value of R2 close to 1 and p-value <0,05. Application of gap planting technology used 41,97% of the total research plot area.
Keyword: Hutan Alam Terdegradasi, Komposisi Jenis, Rehabilitasi, Struktur Tegakan, Tanam Rumpang

Judul: Soil Erosion Study in The Gap Planting Research Area  with Jabon Putih in The PT. Sarmiento Parakantja Timber
Abstrak: Peningkatan produktivitas hutan alam dapat dilakukan dengan menerapkan teknik tanam rumpang. Tujuan dari teknik tanam rumpang adalah untuk merehabilitasi hutan alam terdegradasi dengan penanaman fast growing species lokal non Dipterocarpaceae yang berdaur pendek (5-8 tahun) di dalam areal rumpang. Penelitian ini bertujuan untuk mendapatkan informasi erosi tanah yang terjadi akibat tanam rumpang pada kondisi areal hutan alam, simpukan dan jalur tanam. Penelitian dilakukan pada bulan Mei 2021. Penelitian dilakukan pada dua kelas kelerengan yaitu kelas datar-landai dan kelas sedang. Hasil uji statistik menunjukkan tidak berbeda nyata antara besarnya erosi tanah pada kelas lereng datar-landai dan kelas lereng sedang. Hasil penelitian menunjukan besar erosi tanah yang terjadi secara berturut-turut dari yang terbesar ke terkecil adalah di areal hutan alam, di areal jalur tanam dan di areal jalur simpukan., Increasing the productivity of natural forests can be done by applying the gap planting technique. The purpose of the gap planting technique is to rehabilitate degraded natural forests by planting local intolerant fast-growing species with short cycles (5-8 years) in the gap area. This study aims to obtain information on soil erosion that occurs due to gap planting activities on the condition of natural forest areas, erosion barrier strips, and planting strips. The study was conducted in May 2021. The study was conducted on two slope classes, the flat to sloping class and the moderate class. The result of statistical tests showed that the magnitude of erosion on the flat to sloping class and moderate class was not significantly. The results showed that the amount of soil erosion that occurred successively from the largest to the smallest was the area of natural forest, planting area, and erosion barrier area.
Keyword: erosi tanah, hutan alam terdegradasi, rehabilitasi, tanam rumpang, degraded natural forests, gap planting, rehabilitation, soil erosion

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: