Judul: Pengaruh iklim terhada profitabilitas kentang (Solanum tuberosum) di sentra perkebunan kentang Cikajang-Garut
Abstrak: Potato has a vital role for the Indonesian economy. Potatoes demand will increase caused by population growth and changing consumption patterns in developing countries. Production of potato is influenced by soil water, while soil water is influenced by rainfall, temperature and sunshine duration. Soil water at each planting season varies because of differences in the amount of rainfall. By linking the influence of planting season with soil water availability, profitability of each planting season will be known. There are three Cikajang planting periods: January-April, May-August and September-December. The average potato yield in three planting seasons at Cikajang: January-April amounted to 21 tons/ha, in May-August to 20,2 tons/ha and September- December with average potato yield 17,5 tons/ha. The decrease of production was caused by decreased water availability during the dry season. Highest profitability of potato planting time in the period from January-April amounted to Rp.21,350,000 while May-August amounted to Rp.18,456,250 and the lowest in September-December of Rp.13,195,833.
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Judul: Perhitungan Limpasan Permukaan dan Evapotranspirasi berdasarkan Neraca Air pada Pertanaman Kentang (Solanum Tuberosum L.)
Abstrak: Ketersediaan air merupakan salah satu faktor yang mempengaruhi pertumbuhan, perkembangan serta produksi tanaman kentang. Tanaman kentang cukup banyak dibudidayakan di Indonesia. Tanaman kentang biasa dibudidayakan pada ketinggian lebih dari 1000 m dpl dengan tingkat kemiringan yang cukup tinggi. Kondisi ini mempengaruhi ketersediaan air untuk pertumbuhan tanaman kentang. Tujuan penelitian ini adalah menghitung kehilangan air melalui evapotranspirasi dan limpasan permukaan pada tanaman kentang dengan menggunakan neraca air. Penelitian dilakukan mulai bulan Desember 2009 sampai Maret 2010 di Kebun Percobaan Balitbiogen Pacet-Cipanas, Cianjur. Perhitungan kehilangan air pada tanaman kentang dilakukan dengan pendekatan neraca air dengan persamaan ETat+Rot = θt-1-θt+Pt, dimana θt = kadar air tanah hari ke t, θt-1 = kadar air hari ke t-1, dan ETat+Rot = kehilangan air karena evapotranspirasi aktual dan runoff hari ke t. Evapotranspirasi actual diasumsikan sebesar 4 mm/hari. Hasil penelitian ini menunjukkan bahwa kondisi dimana curah hujan tinggi, terjadi runoff yang besar karena kapasitas infiltrasi dan perkolasi yang terbatas, dan tetap terjadi evapotranspirasi. Hal ini dapat mengurangi kadar air tanah selama masa pertumbuhan tanaman kentang. Kadar air tanah yang lebih tinggi menghasilkan laju pertumbuhan tanaman kentang yang lebih tinggi walaupun jarak tanamnya lebih rapat. Di samping kadar air tanah, ukuran bibit sangat menentukan hasil panen kentang.
Keyword: Potato, Water balance, Evapotranpiration, Runoff, Soil water

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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