Judul: Faktor iklim dan tanaman ubijalar: Analisis pola tanam dan profit usaha tani di Desa Cikarawang
Abstrak: Sweet potato is one of the crop that can be used by Indonesian people as a staple or a processed foods. Sweet potato becomes the main commodity in Cikarawang village. Cikarawang has average rainfall of about 314 mm/month, average monthly temperature 25 oC to 28 oC, and average monthly sunshine duration of 64%. Cikarawang has three cropping patterns; cropping pattern A: sweet potato (month January-April) – sweet potato (May-August) – paddy (September-December), cropping pattern B: sweet potato (January-April) – peanut (May-August) – paddy (September-December), and cropping pattern C: only plants sweet potato all years. There were differences in productivity, production costs, and profitability in the three types of cropping pattern in Cikarawang. The analysis showed that temperature, rainfall, and sunshine duration affect the production costs and profit. A high rainfall, low temperature, high surplus and runoff caused high production costs. High production mostly commonly occurred in period of January-April. The survey indicated that cropping pattern A is the most profitable resulted from highest profit.
Keyword: Bogor Agricultural University (IPB), sweet potato, profit, cropping pattern, climate factor

Judul: Economic Efficiency Analysis of Sweet Potato Farming in Cikarawang Village, Dramaga District, Bogor Regency
Abstrak: Desa Cikarawang merupakan salah satu daerah sentra produksi ubi jalar di Kecamatan Dramaga. Produktivitas ubi jalar di Desa Cikarawang cenderung menurun tiap tahunnya. Produksi dan produktivitas ubi jalar yang menurun diduga disebabkan oleh alokasi input produksi yang tidak optimal. Produksi ubi jalar yang rendah akan berpengaruh terhadap pendapatan yang diterima oleh petani. Penelitian ini dilakukan untuk menganalisis pendapatan usahatani ubi jalar, menganalisis faktor-faktor yang memengaruhi produktivitas ubi jalar, dan menganalisis efisiensi penggunaan input produksi yang optimal. Metode analisis data yang digunakan yaitu analisis pendapatan usahatani, analisis regresi linear berganda, dan metode Nilai Produk Marginal. Hasil penelitian ini menunjukkan bahwa usahatani menguntungkan karena pendapatan bernilai positif dan R/C ratio lebih besar dari satu. Faktor-faktor yang berpengaruh secara positif dan signifikan terhadap produktivitas ubi jalar adalah pupuk kandang dan pestisida cair. Faktor produksi yang belum efisien pada usahatani ubi jalar yaitu pupuk kandang dan pestisida cair sehingga perlu untuk ditambah. Kata kunci: analisis pendapatan, efisiensi ekonomi, NPM, produktivitas, R/C ratio, Cikarawang Village in Dramaga District is one of the main sweet potato production areas. The productivity of sweet potatoes in Desa Cikarawang tends to decrease each year. The decreasing production and productivity of sweet potatoes are suspected to be caused by suboptimal allocation of production inputs. The low production of sweet potatoes will affect the income received by farmers. This research was conducted to analyze the income from sweet potato farming, analyze the factors affecting sweet potato productivity, and analyze the efficiency of optimal production input usage. The data analysis methods used were farm income analysis, multiple linear regression analysis, and the Marginal Product Value method. The results of this study indicate that farming is profitable because the income is positive and the R/C ratio is greater than one. Factors that positively and significantly affect sweet potato productivity are manure and liquid pesticides. The production inputs that are not yet efficient in sweet potato farming are manure and liquid pesticides, which therefore need to be increased.
Keyword: produktivitas, R/C ratio, analisis pendapatan, efisiensi ekonomi, NPM

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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