Judul: Identification of Changes in Food Consumer Behavior during the Covid-19 Pandemic in Jabodetabek
Abstrak: Adanya pandemi Covid-19, kemungkinan dapat mengakibatkan perubahan pola perilaku konsumen pangan. Penelitian ini bertujuan untuk mengetahui produk pangan yang dibeli selama pandemi Covid-19, mengidentifikasi cara pembelian produk pangan dan tempat pembeliannya, mengidentifikasi faktor yang memengaruhi konsumen dalam membeli produk pangan, serta membandingkan perilaku konsumen sebelum dan selama pandemi Covid-19 di wilayah Jabodetabek. Metode yang digunakan yaitu survei online dengan teknik purposive sampling. Data dianalisis menggunakan analisis deskriptif dan analisis korelasi. Hasil survei menunjukkan bahwa terdapat produk yang mengalami peningkatan pembelian yaitu sayur dan buah segar, telur, mi instan, air mineral, minuman herbal, serta jus buah. Produk yang mengalami penurunan pembelian yaitu minuman karbonasi, minuman energi, sirup, makanan siap saji, serta makanan kaleng. Produk yang tidak mengalami perubahan pembelian diantaranya beras, daging segar maupun olahan, ikan dan seafood, roti, biskuit dan kue kering, susu dan olahannya, makanan ringan, makanan beku, sereal sarapan, bumbu masakan instan, teh siap minum, minuman isotonik, serta konfeksioneri. Terjadi pula peningkatan cara pembelian melalui online store selama pandemi Covid-19. Hasil uji Chi-Square menunjukkan terdapat 13 faktor yang memengaruhi pembelian beberapa produk pangan selama pandemi Covid-19 diantaranya yaitu domisili, jenis kelamin, usia, pendidikan, pekerjaan, merek, sensori, manfaat, kemudahan diperoleh, kandungan gizi, keamanan pangan, harga, serta ketersediaan., The existence of Covid-19 pandemic is thought to have resulted in changes in food consumer behavior patterns. This study aims to determine the food products purchased during Covid-19 pandemic, identify how to purchase food products and where to buy them, identify factors that influence consumers to buy food products, and compare consumer behavior before and during the Covid-19 pandemic in Jabodetabek. The method used is an online survey with purposive sampling technique. Data were analyzed using descriptive analysis and correlation analysis. The survey results showed that there were products that experienced an increase in purchases, such as fresh vegetables and fruit, eggs, instant noodles, mineral water, herbal drinks, and fruit juices. Products that experienced a decline in purchases were carbonated drinks, energy drinks, syrups, ready-to-eat food and canned food. Products that are regularly purchased include rice, fresh and processed meat, fish and seafood, bread, biscuits and pastries, milk and processed foods, snacks, frozen foods, breakfast cereals, instant cooking spices, ready-to-drink tea, isotonic drinks, and confectionery. There has also been an increase in ways of purchasing via online stores during the Covid-19 pandemic. The results of Chi-Square test showed that there were 13 factors that influenced the purchase of several food products during the Covid-19 pandemic including domicile, gender, age, education, occupation, brand, sensory, benefits, accessibility, nutritional content, food safety, price, and product availability.
Keyword: Covid-19, Perilaku konsumen, Survei online, consumer behavior, covid-19, online survey

Judul: Changes in the Beverages and Nutritional Supplements Consumption of Adults in Java Related to the Covid-19 Pandemic
Abstrak: Penyebaran Covid-19 yang cenderung meningkat memengaruhi kondisi sosial ekonomi masyarakat yang berpotensi memengaruhi konsumsi makanan, minuman, dan suplemen gizi selama pandemi. Penelitian ini bertujuan menganalisis perubahan konsumsi minuman dan suplemen gizi pada orang dewasa di Jawa sehubungan pandemi Covid-19. Desain cross-sectional study melibatkan subjek berusia 25-54 tahun. Analisis statistik yang digunakan adalah uji Mann Whitney, Spearman, dan Chi square. Hasil penelitian menunjukkan peningkatan konsumsi yang signifikan pada air minum dalam kemasan, air minum tidak dalam kemasan, minuman isotonik, minuman berenergi, susu, jus buah, air kelapa, dan minuman herbal saat pandemi dibanding sebelum pandemi. Sebaliknya, konsumsi minuman teh, kopi, dan bersoda menurun signifikan. Terdapat peningkatan yang signifikan pada konsumsi suplemen gizi tunggal dan multivitamin. Sementara konsumsi suplemen gizi lainnya menurun signifikan. Terdapat hubungan yang signifikan positif antara perubahan konsumsi minuman dan suplemen gizi dengan provinsi, pekerjaan, besar keluarga, pendapatan, pengeluaran pangan, kekhawatiran kekurangan pangan, porsi makan, frekuensi makan dan ngemil, cara memenuhi kebutuhan pangan, kondisi kesehatan, penyakit kronis, status penyintas Covid-19, kekhawatiran kesehatan, aktivitas fisik, dan berat badan subjek. Sementara itu, terdapat hubungan yang signifikan negatif antara perubahan konsumsi minuman dan suplemen gizi dengan usia dan pendidikan subjek.
Keyword: adults in Java, beverages consumption, Covid-19 pandemic, nutritional supplements consumption, online survey

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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