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: Competitiveness dan Factors Influencing Indonesian Ribbed Smoked Sheet (RSS) Natural Rubber Export.
Abstrak: Ekspor Indonesia didominasi oleh sektor non-migas pada tahun 2020 dan Indonesia berada di posisi tiga besar negara pengekspor karet alam RSS pada tahun 2020. Namun jika dibandingkan dengan ekspor karet alam Technically Specified Natural Rubber, ekspor karet alam RSS Indonesia masih lebih sedikit meskipun harga per kilogram karet alam RSS lebih mahal daripada karet alam TSNR. Penelitian ini bertujuan untuk menganalisis daya saing dan faktor-faktor yang memengaruhi ekspor karet alam RSS Indonesia ke negara tujuan utama ekspor. Metode yang akan digunakan adalah Revealed Comparative Advantage (RCA), Export Product Dynamic (EPD), Porter’s Diamond, X-model, dan regresi data panel. Vietnam dan Thailand merupakan negara pesaing Indonesia pada analisis daya saing. Hasil penelitian menunjukkan bahwa karet RSS Indonesia memiliki keunggulan komparatif pada lima pasar tujuan utama. Ekspor komoditas ini berkembang paling baik bagi Indonesia di China dan India. Karet RSS Indonesia memiliki aspek keunggulan di faktor permintaan dan faktor industri penunjang dan terkait. Regresi data panel memperlihatkan bahwa faktor-faktor yang memengaruhi ekspor komoditas ini adalah GDP negara tujuan, volume ekspor tahun sebelumnya, nilai tukar Rupiah terhadap Dolar AS, dan nilai tukar riil efektif negara tujuan. Sementara itu, tahun pembatasan ekspor karet alam oleh International Tripartite Rubber Council tidak berpengaruh signifikan., Indonesia’s export was dominated by non-oil & gas sector in 2020 and Indonesia placed on the top three nation of RSS Rubber exporter in 2020. Compared with Technically Specified Natural Rubber exports, Indonesian RSS Natural Rubber exports is still far behind despite RSS Rubber price per kilogram is higher than that of TSNR. This paper aims to analyze competitiveness of Indonesian RSS Natural Rubber in main countries of destination and to analyze factors influencing its export volume to said countries. Methods used in this paper are Revealed Comparative Advantage, Export Product Dynamic, Porter’s Diamond, X-model, and Panel Data Regression. Result shows that Indonesia’s RSS natural rubber has competitive advantage in all five main export destination. This Indonesian export commodity has the highest market growth in China and India. Indonesian RSS Rubber has its strength in demand factor and supporting and related industries. Lastly, according to panel data regression, factors influencing export of this commodity are GDP of importer country, previous year export volume towards the importer country, importer country’s real effective exchange rate, and US Dollar to Rupiah exchange rate. Meanwhile, natural rubber export restriction by International Tripartite Rubber Council doesn’t have significant effect.
Keyword: comparative advantage, competitive advantage, international trade

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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