Judul: Market Structure and Competitiveness of  Indonesian Natural Rubber in the United States
Abstrak: Karet alam Indonesia berperan penting untuk meningkatkan perekonomian nasional melalui ekspor karet alam ke berbagai negara, termasuk Amerika Serikat. Indonesia perlu melakukan identifikasi posisi dan daya saing karet alam di antara negara pesaing serta peluang pasarnya ke Amerika Serikat. Tujuan penelitian ini adalah menganalisis struktur pasar, keunggulan komparatif dan kompetitif karet alam Indonesia di pasar Amerika Serikat. Analisis dilakukan pada periode tahun 2008 dan 2019 melalui metode Herfindahl Index (HI), Concentration Ratio (CR4), Revealed Comparative Advantage (RCA), Export Product Dynamic (EPD), dan Diamond’s Porter. Hasil analisis menemukan bahwa struktur pasar karet alam Indonesia adalah monopoli dan cenderung sedikit oligopoli. Dibandingkan dengan negara-negara eksportir lainnya, karet alam Indonesia memiliki keunggulan komparatif di pasar Amerika Serikat dengan nilai RCA>1. Keunggulan kompetitif karet alam Indonesia di Amerika Serikat mengalami penurunan dari posisi lost opportunity pada periode pertama (2008-2011) menjadi retreat pada periode ketiga (2016-2019). Hasil dari Diamond’s Porter menunjukkan bahwa terdapat tujuh faktor keunggulan kompetitif dan tiga faktor kelemahan dalam industri karet alam di Indonesia., Indonesian natural rubber plays a significant role in improving the national economy by exporting natural rubber to various countries, including the United States. Indonesia must identify its natural rubber position and competitiveness among competing countries and market opportunities in the US. This study aims to analyze the market structure, comparative advantage and competitiveness of Indonesian natural rubber in the US market. The analysis was carried out in the period 2008 and 2019 through methods, including Herfindahl Index (HI), Concentration Ratio (CR4), Revealed Comparative Advantage (RCA), Export Product Dynamic (EPD), and Diamond's Porter. The analysis found that the natural rubber market structure in Indonesia is monopolistic and tends to be oligopolistic. Compared to other exporting countries, Indonesian natural rubber has comparative advantage in the US market, as indicated by the RCA>1. The competitiveness of Indonesian natural rubber in the US decline overtime from the lost opportunity position in the first period (2008-2011) to retreat in the third period (2016-2019). The diamond's porter results show that there are seven competitive advantage factors and three weakness factors in Indonesia's natural rubber industry.
Keyword: concentration ratio, diamond’s porter, EPD, herfindahl index, RCA

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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