Judul: Komposisi Jenis Tumbuhan Bawah pada Tegakan Sengon (Paraserianthes falcataria, L. Nielsen) (Studi Kasus di Areal Kampus IPB Darmaga, Bogor)
Abstrak: Sengon (Paraserianthes falcataria L. Nielsen) is a tree species which has high economy value and potential for agroforestry development. Information on the diversity of undergrowth species at sengon stands has not been much known. Undergrowth vegetation have ecological functions to keep the ecosystem balance and as addition, it can also take a role as a weed in the monoculture plants cultivation. In other hand, some undergrowth species have been identified as beneficial plants. This research aims to know the composition and diversity of undergrowth species at sengon stands. Results of inventory at the age of 5 years sengon stands, found 41 species from 23 families which dominated by the type of Ottochloa nodosa, Paspalum conjugatum, Lepistemon binectarifer, and Asytasia gangetica. At the age of 15 years, found 34 species from 20 families which dominated by the type of Ottochloa nodosa, Oplismenus compositus, Axonophus compressus, and Asytasia gangetica. The diversity levels of species according to the classification of Magurran (1998) at age 5 years sengon stands of 2.11 (medium), while at the age of 15 years sengon stands of 1.86 (low). Meanwhile, in the calculation of community similarity levels, condition of the community based on the number of types and abundance of individuals of each species is different (IS ≤ 75%), with the value 48.42. Among the species found, there are several types of plants which have potency as medicinal plants, such as pacing (Costus speciosus) and nut-grass (Cyperus rotundus), as food resource, such as taro (Colocasia esculenta) and takokak (Solanum jamaicense). The types of cover crops and fodder such as ornamental peanut (Arachis pintoi) and sentro (Centrocema pubescens). The type of ornamental plants such as wedelia (Wedelia trilobata) and taro (caladium bicolor). Furthermore, there is the type of plants which has potency as a fuel source such as iles-iles (Amorphopallus variabilis).
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Judul: Composition of Undergrowth Types at Sengon (Paraserianthes falcataria L. Nielsen) Stands
Abstrak: Penelitian ini bertujuan untuk mengetahui komposisi dan keanekaragaman jenis tumbuhan bawah pada tegakan sengon. Hasil inventarisasi pada tegakan sengon umur 5 tahun ditemukan 41 jenis dari 23 famili yang didominasi jenis Ottochloa nodosa, Paspalum conjugatum, Lepistemon binectarifer, dan Asytasia gangetica. Pada umur 15 tahun dijumpai 34 jenis dari 20 famili yang didominasi jenis O. nodosa, Oplismenus compositus, Axonophus compressus, dan A. gangetica. Tingkat keanekaragaman jenis menurut klasifikasi Magurran (1998) pada tegakan sengon umur 5 tahun sebesar 2,11 (sedang), sedangkan pada tegakan sengon umur 15 tahun sebesar 1,86 (rendah). Sementara itu, pada perhitungan tingkat kesamaan komunitas, kondisi komunitas berdasarkan jumlah jenis dan kelimpahan individu setiap jenisnya tergolong berbeda (IS ≤ 75%), yaitu sebesar 48,42. Dari jenis-jenis yang ditemukan terdapat beberapa jenis yang berpotensi sebagai tumbuhan obat, seperti pacing (Costus speciosus), dan rumput teki (Cyperus rotundus), Sebagai bahan pangan, seperti talas (Colocasia esculenta) dan takokak (Solanum jamaicense). Jenis-jenis penutup tanah dan pakan ternak seperti kacang hias (Arachis pintoi), dan sentro (Centrocema pubescens). Jenis tanaman hias seperti wedelia (Wedelia trilobata), dan keladi (Caladium bicolor). Serta terdapat pula jenis yang berpotensi sebagai sumber bahan bakar yaitu iles-iles (Amorphopallus variabilis).
Keyword: Species composition,, Species diversity, Undergrowth species

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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