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: Comparison of Indonesia's Natural Rubber Derivative Product Competitiveness with ITRC Member Countries and Determinants of Exports to the United States
Abstrak: Indonesia memiliki potensi penerimaan dari produk turunan karet alam, seperti ban serta pakaian dan aksesori pakaian. Namun, Indonesia belum memiliki spesialisasi ekspor dibandingkan dengan Thailand dan Malaysia. Pasar utama, yaitu Amerika Serikat, juga menjadi tujuan ekspor utama bagi Thailand dan Malaysia, sehingga meningkatkan persaingan. Penelitian ini bertujuan untuk menganalisis daya saing produk turunan karet alam Indonesia dengan negara anggota ITRC lainnya ke Amerika Serikat menggunakan metode Revealed Comparative Advantage (RCA), Export Product Dynamic (EPD), X- Model, dan Indeks Spesialisasi Perdagangan (ISP). Selanjutnya, menganalisis faktor-faktor yang memengaruhi ekspor produk turunan karet alam Indonesia ke Amerika Serikat menggunakan regresi linier berganda. Hasil penelitian menunjukkan bahwa, produk ban Indonesia dan Thailand memiliki potensi pengembangan pasar optimis di Amerika Serikat. Hal tersebut didukung kematangan dan pertumbuhan dari produk ban Thailand dan Indonesia. Sebaliknya, hanya produk pakaian dan aksesori pakaian Indonesia yang memiliki potensi pengembangan pasar optimis di Amerika Serikat. Padahal, ketiga negara sudah didukung oleh kematangan dari produk pakaian dan aksesori pakaian. Faktor-faktor yang signifikan memengaruhi volume ekspor ban Indonesia adalah PDB Amerika Serikat, produksi kendaraan bermotor Amerika Serikat, dan dummy GSP. Adapun faktor-faktor yang signifikan memengaruhi volume ekspor pakaian dan aksesori pakaian Indonesia adalah harga ekspor, PDB Amerika Serikat, dan dummy COVID-19., Indonesia has potential revenue from natural rubber derivative products, such as tires with apparel and clothing accessories. However, Indonesia lacks export specialization compared to Thailand and Malaysia. The main market, the United States, is also the main export destination for Thailand and Malaysia, increasing competition. This study aims to analyze the competitiveness of Indonesia's natural rubber derivative products with other ITRC member countries to the United States using the Revealed Comparative Advantage (RCA), Export Product Dynamic (EPD), X-Model, and Index of Trade Specialization (ISP) methods. Furthermore, it analyzes the factors that influence the export of Indonesian natural rubber derivative products to the United States using multiple linear regression. The results showed that Indonesian and Thailand tire products have optimistic market development potential in the United States. This is supported by the maturity and growth of Thailand and Indonesian tire products. In contrast, only Indonesian apparel and clothing accessories products have optimistic market development potential in the United States. In fact, the three countries are already supported by the maturity of apparel and clothing accessories products. The factors that significantly affect the export volume of Indonesian tires are the GDP of the United States, production of motor vehicles in the United States, and dummy GSP. The factors that significantly affect the export volume of Indonesian apparel and clothing accessories are export prices, GDP of the United States, and dummy COVID-19.
Keyword: ban, sarung tangan

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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