Judul: Analisis Capital Asset Pricing Model (CAPM) pada Saham Sektor Teknologi Periode Sebelum dan Selama Pandemi COVID- 19
Abstrak: Pandemi Covid-19 membuat masyarakat memilih untuk menabung saham di pasar modal. Saham sektor teknologi menjadi saham yang primadona karena volume perdagangan yang meningkat hingga 7,3 kali selama pandemi. Capital Asset Pricing Model (CAPM) adalah model untuk melihat tingkat return yang diharapkan dan bertujuan untuk membantu investor dalam mengambil keputusan investasi. Penelitian ini bertujuan untuk melihat perbedaan saham sektor teknologi pada periode sebelum dan selama pandemi menggunakan metode CAPM serta ujit berpasangan. Waktu penelitian dimulai Januari hingga Maret 2023 di website Bursa Efek Indonesia dengan menggunakan metode penarikan sampel yaitu purposive sampling. Metode deskriptif kuantitatif digunakan dalam penelitian ini yang menggunakan data sekunder berupa laporan keuangan perusahaan sektor teknologi yang terdapat di Bursa Efek Indonesia periode Januari 2018 hingga Juni 2022 sebanyak 7 sampel penelitian. Berdasarkan hasil penelitian, 7 saham memiliki rata-rata return yang negatif sebelum pandemi dan return positif pada periode selama pandemi. Terdapat 1 saham efisien periode sebelum pandemi dan 6 saham tidak efisien serta 7 saham tergolong saham efisien selama pandemi. Dari hasil uji-t berpasangan menunjukkan bahwa adanya perbedaan yang signifikan antara return pengembalian individu pada sebelum dan selama pandemi., The Covid-19 pandemic made people more active in saving, one of which is investing in the capital market. Stocks in the technology sector were excellent stocks because the trading volume increased by up to 7.3 times during the pandemic. The Capital Asset Pricing Model (CAPM) was a model to see the expected rate of return and aimed to assist investors in making investment decisions. This study aimed to look at differences in technology sector stocks in the period before and during the pandemic using the CAPM method and paired ttest. The research time started from January to March 2023 on the website of the Indonesia Stock Exchange using a purposive sampling method. A quantitative descriptive method was used in this study and used secondary data in the form of financial statements of technology sector companies listed on the Indonesia Stock Exchange for the period January 2018 to June 2022 as many as 7 research samples. Based on the results of the study, 7 stocks had an average negative return before the pandemic and positive returns during the pandemic. There was 1 efficient stock in the pre-pandemic period and 6 inefficient shares, and 7 shares were classified as efficient shares during the pandemic. The results of the paired t-test showed that there was a significant difference between individual returns before and during the pandemic.
Keyword: Before and During Pandemic, CAPM, Investment Decision, Paired T-Test, Technology Sector Stocks

Judul: Optimal Portfolio Formation with Passive and Active Strategies during Pre, Period, and Post Covid-19 Pandemic
Abstrak: Munculnya Pandemi Covid-19 menyebabkan peningkatan inefisiensi dan risiko pasar saham. Untuk mengurangi risiko, dilakukan diversifikasi dengan membentuk portofolio. Dikarenakan investor tidak boleh berinvestasi pada satu sektor saham saja, pembentukan portofolio pada penelitian ini dilakukan pada perwakilan sebelas sektor saham IDX-IC di BEI. Penelitian ini dilaksanakan pada April hingga Juli 2024 menggunakan metode Markowitz dengan strategi pasif dan aktif. Hasil penelitian ini menunjukkan bahwa Pandemi Covid-19 menyebabkan terjadinya penurunan return dan peningkatan risiko portofolio. Ditinjau dari segi komposisi saham, pada periode pra pandemi, sektor yang mencatatkan komposisi terbesar adalah sektor Barang Konsumen Primer, kemudian pada periode masa pandemi yaitu sektor Perindustrian dan Barang Konsumen Non-Primer, dan pada periode pasca pandemi yaitu sektor Keuangan. Strategi optimal pembentukan portofolio jika ingin meminimalkan risiko adalah strategi pasif, sementara jika ingin memaksimalkan return adalah strategi aktif., The emergence of the Covid-19 Pandemic has led to an increase in stock market inefficiency and risk. To decrease the risk, diversification is conducted by forming a portfolio. Due to the investor should not invest in only one stock sector, portfolio formation in this research was conducted on representatives of eleven IDX-IC stock sectors on the IDX. This research was conducted from April to July 2024 using the Markowitz method with passive and active strategies. The results of this research show that the Covid-19 Pandemic causes a decrease in return and an increase in portfolio risk. In terms of stock composition, in the pre-pandemic period, the sector that has the largest composition is the Primary Consumer Goods sector, while in the pandemic period is the Industry and Non-Primary Consumer Goods sectors, and in the post-pandemic period is the Financial sector. The optimal strategy for portfolio formation if you want to minimize risk is a passive strategy, while if you want to maximize returns is an active strategy.
Keyword: Markowitz Method, Optimal Portfolio, Stock, Passive & Active Strategy

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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