Judul: Comparative Competitiveness of Indonesia and Thailand Natural Rubber Export in the Destination Countries and its Influencing Factors.
Abstrak: Indonesia memiliki areal karet alam terluas di dunia, namun perannya sebagai eksportir karet alam masih di bawah Thailand. Selama 2013-2022, Indonesia dan Thailand memiliki kesamaan beberapa negara tujuan sehingga menimbulkan persaingan ekspor antara kedua negara tersebut. Penelitian ini mengidentifikasi dan membandingkan daya saing ekspor karet alam Indonesia dan Thailand dengan menggunakan metode RCA, EPD, dan X-Model. Identifikasi faktor-faktor yang memengaruhi volume ekspor karet alam Indonesia digunakan regresi data panel. Secara keseluruhan, hasil perhitungan nilai RCA Indonesia 36,55 dan Thailand 29,59 menunjukkan Indonesia memiliki daya saing yang lebih unggul diantaranya di AS, Brazil, India, Jepang, dan Turki, sedangkan Thailand hanya unggul di China dan Korea Selatan. Analisis X-Model menunjukkan karet alam Indonesia memiliki pasar potensial di AS, China, India, Jepang, dan Turki. Sementara Brazil dan Korea Selatan merupakan pasar kurang potensial. Di sisi lain, Thailand memiliki pasar optimis di AS dan Turki, pasar potensial di China, India, Jepang, dan Korea Selatan, pasar kurang potensial di Brazil. Hasil estimasi regresi data panel menunjukkan variabel PDB riil importir, nilai RCA Indonesia, harga karet alam Thailand, dan dummy Covid-19 berpengaruh signifikan terhadap volume ekspor karet alam Indonesia.
Keyword: natural rubber, RCA, EPD

Judul: Analysis of Indonesian Natural Rubber Export Performance to Destination Country
Abstrak: Indonesia merupakan salah satu negara eksportir terbesar karet di dunia, namun demikian nilai ekspor cenderung berfluktuatif. Tujuan penelitian ini adalah untuk menganalisis kinerja nilai karet alam Indonesia ke negara tujuan utama dengan kode HS 4001 pada periode 2012-2021. Metode yang digunakan dalam penelitian ini dalam menganalisis daya saing adalah Revealed Comparative Advantage (RCA), Export Dynamic (EPD), dan X model. Penelitian ini juga menggunakan gravity model dalam mengestimasi determinan permintaan ekspor karet alam Indonesia ke negara tujuan utama. Berdasarkan hasil RCA menunjukkan karet alam Indonesia berdaya saing tinggi. Analisis EPD menunjukkan pangsa pasar lost opportunity di USA, Kanada, dan China, falling star di Jepang, India, dan Korea Selatan, dan retreat di Brazil dan Turki. Analisis X-Model menunjukkan pengembangan pangsa pasar potensial hampir di seluruh negara kecuali Brazil dan Turki. Hasil analisis gravity model menunjukkan, GDP negara tujuan utama dan harga komoditas berpengaruh positif dan signifikan terhadap nilai ekspor karet alam Indonesia. Nilai GDP riil Indonesia dan jarak ekonomi memiliki pengaruh negatif terhadap nilai ekspor karet alam Indonesia. Sementara nilai tukar tidak berpengaruh signifikan., Indonesia is one of the largest rubber exporters in the world, however, the export value tends to fluctuate. The purpose of this study was to analyze the value performance of Indonesian natural rubber to the main destination countries with the HS code 4001 in the 2012-2021 period. The method used in this study in analyzing competitiveness is Revealed Comparative Advantage (RCA), Export Dynamic (EPD), then X model. This research also uses gravity model in estimating the determinants of demand for Indonesia's natural rubber exports to the main destination countries. Based on RCA results, Indonesia's natural rubber is highly competitive. EPD analysis shows market share lost opportunity in the USA, Canada, and China, falling star in Japan, India, and South Korea, and retreat in Brazil and Turkey. X-Model analysis shows the potential market share development in almost all countries except Brazil and Turkey. Analysis results gravity model shows, the GDP of the main destination countries and commodity prices have a positive and significant effect on the export value of Indonesia's natural rubber. Indonesia's real GDP value and economic distance have a negative effect on the value of Indonesia's natural rubber exports. While the exchange rate has no significant effect.
Keyword: EPD, Gravity Model, Natural rubber, RCA, X-Model

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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