Judul: The Impact of Covid-19 on the agricultural sector  GRDP in Central Java  Province
Abstrak: Sektor pertanian memiliki peran penting dalam pembangunan ekonomi daerah khususnya di Provinsi Jawa Tengah. Provinsi Jawa Tengah mendapat julukan sebagai salah satu “daerah lumbung pangan nasional”. Sektor pertanian memiliki fungsi primer sebagai penyedia bahan pangan hingga persebaran distribusi pendapatan masyarakat melalui tingginya tingkat kesempatan kerja. Adanya pandemi Covid-19 menyebabkan perubahan struktur ekonomi dan berdampak pada penurunan laju pertumbuhan ekonomi daerah. Salah satu sektor yang berpeluang emas untuk membangkitkan pertumbuhan ekonomi adalah sektor pertanian. Penelitian ini bertujuan untuk menganalisis faktor-faktor yang memengaruhi PDRB sektor pertanian di Jawa Tengah, membandingkan PDRB sektor pertanian Jawa Tengah antara data aktual dengan hasil peramalan SARIMA selama masa pandemi Covid-19 serta memproyeksikan PDRB sektor pertanian selama empat tahun. Penelitian ini menggunakan metode regresi data panel dan model Seasonal Autoregressive Integrated Moving Average (SARIMA). Hasil penelitian menunjukan bahwa: 1) faktor-faktor yang memengaruhi PDRB sektor pertanian di Jawa Tengah secara positif dan signifikan adalah tenaga kerja sektor pertanian dan kredit pertanian sedangkan faktor negatifnya adalah Covid-19; dan 2) Pandemi Covid-19 berpengaruh terhadap menurunnya pertumbuhan sektor pertanian di Jawa Tengah dengan total prediksi penurunan PDRB sektor pertanian sebesar 5,67 triliun rupiah serta proyeksi pertumbuhan sektor pertanian sampai dengan tahun 2024 terus mengalami peningkatan dengan pertumbuhan yang lambat rata-rata 2,38%., The agricultural sector has an important role in regional economic development, especially in Central Java Province. Central Java Province has earned the nickname as one of the “national food storage areas”. The agricultural sector has a primary function as a provider of food and distribution of community income through high levels of employment opportunities. The Covid-19 pandemic has caused changes in the economic structure and had an impact on reducing the rate of regional economic growth. One sector that has a golden opportunity to generate economic growth is the agricultural sector. This research aims to analyze the factors that influence the GRDP of the agricultural sector in Central Java, compare the GRDP of the Central java agricultural sector between actual data and SARIMA forecasting results during the Covid-19 pandemic and project the GRDP of the agricultural sector for four years. This research uses the panel data regression method and the Seasonal Autoregressive Integrated Moving Average (SARIMA) model. The research results show that: 1) the factors that positively and significantly influence the GRDP of agricultural sector in Central Java Province are agricultural sector labor and agricultural credit, while the negative factor is Covid-19; and 2) the Covid-19 pandemic has resulted in a decline in the growth of the agricultural sector in Central Java with a total predicted GRDP loss in the agricultural sector of 5,67 trillion rupiah and the projected growth of the agricultural sector until 2024 continues to increase with slow growth averaging 2,38%.
Keyword: Data panel, PDRB sektor pertanian, RPJMD, Seasonal Autoregressive Integrated Moving Average

Judul: Effect of the Covid-19 Pandemic on the Provincial Rice Prices in Java
Abstrak: Pandemi Covid-19 yang muncul pertama kali di Kota Wuhan dan masuk ke Indonesia pada awal tahun 2020 dan penyebarannya sangat pesat terutama di Pulau Jawa. Pandemi Covid-19 mengakibatkan penurunan Produk Domestik Bruto pada beberapa sektor di Indonesia, namun data dari BPS menyebutkan bahwa pertumbuhan PDB pada sektor pertanian pada tahun 2020 sampai 2021 tumbuh konsisten dan positif. Pertumbuhan dalam sektor pertanian terjadi pada beberapa subsektor pertanian termasuk tanaman pangan beras. Beras merupakan komoditas pangan strategis dan karena ketersediannya untuk melindungi ketahanan pangan nasional dan untuk menjaga stabilitas perekonomian di Indonesia. Penelitian ini bertujuan untuk mengestimasi tingkat fluktuasi harga beras provinsi di Pulau Jawa sebelum dan selama pandemi Covid-19 serta faktor-faktor yang memengaruhi harga beras provinsi di Pulau Jawa tahun 2018 sampai 2021 dengan menggunakan metode data panel. Hasil penelitian menunjukan fluktuasi harga beras di Provinsi Pulau Jawa mencapai puncaknya pada awal pandemi Covid-19 pada kuartal 1 tahun 2020, tetapi kuartal selanjutnya fluktuasinya lebih rendah karena adanya penurunan permintaan dan daya beli masyarakat serta adanya kebijakan stabilisasi harga pemerintah. Harga beras di Provinsi Pulau Jawa dipengaruhi oleh harga beras internasional, konsumsi per kapita, Harga Pembelian Pemerintah, dan Covid-19 sedangkan produksi beras tidak berpengaruh terhadap harga beras provinsi di Pulau Jawa. Selain itu, dalam jangka pendek dan jangka panjang, setiap peningkatan harga beras internasional, konsumsi per kapita, HPP, dan kasus Covid-19 akan menaikan harga beras sedangkan setiap peningkatan produksi beras akan menurunkan harga beras provinsi di Pulau Jawa. Saran bagi kebijakan pemerintah yaitu perlunya upaya stabilisasi harga beras dengan peningkatan produksi beras., The Covid-19 pandemic first appeared in the city of Wuhan and entered Indonesia in early 2020 and spread very rapidly, especially on the island of Java. The Covid-19 pandemic has resulted in a decrease in Gross Domestic Product in several sectors in Indonesia, but data from BPS states that GDP growth in the agricultural sector from 2020 to 2021 grows consistently and positively. Growth in the agricultural sector occurred in several agricultural sub-sectors including rice food crops. Rice is a strategic food commodity of its availability to protect national security and to maintaining stability in Indonesia. This study aims to estimate the level of fluctuations in provincial rice prices in Java before and during the Covid-19 pandemic and the factors that affect provincial rice prices in Java in 201fromto 2021 using the panel data method. The results showed that rice price fluctuations in Java Island Province reached its peak at there beginning of the Covid-19 pandemic in the first quarter of 2020, but the next in quarter the fluctuations were lower due to a decline in public demand and purchasing power and the government's price stabilization policy. Rice prices in Java Island Province are influenced by international rice prices, per capita consumption, Government Purchase Prices, and Covid-19, while rice production has no effect on provincial rice prices in Java. In addition, in the short and long term, every increase in international rice prices, per capita consumption, HPP, and cases of Covid-19 will increase the price of rice while every increase in rice production will reduce the price of provincial rice in Java.
Keyword: Covid-19, fluctuation, Java Island, panel data, provincial rice prices

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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