Judul: Overreaction Phenomenon on Sharia Stocks in Indonesia During COVID-19 Pandemic
Abstrak: Pandemi COVID-19 memberikan dampak yang meluas hingga sektor pasar modal. Penurunan harga saham terjadi pada saham syariah Indonesia di masa tersebut. Berbagai informasi selama pandemi membuat investor memberi reaksi yang berlebihan dan menyebabkan ketidakefisienan pasar. Penelitian ini bertujuan untuk mengidentifikasi fenomena overreaction pada saham syariah serta menganalisis faktor-faktor yang memengaruhinya. Pendekatan yang digunakan dalam penelitian ini ialah event study. Hasil uji beda menunjukkan bahwa fenomena overreaction terjadi pada portofolio saham winner saat pengumuman kasus COVID-19 pertama di Indonesia (Event 1), sedangkan pada peristiwa penerbitan program PEN (Event 3), kedatangan vaksin COVID-19 di Jakarta (Event 6), dan kenaikan kasus positif harian COVID-19 tertinggi per-Agustus 2021 (Event 10) fenomena overreaction terjadi pada portofolio saham winner-loser. Hasil cross sectional regression menunjukkan bahwa faktor-faktor yang signifikan memengaruhi fenomena overreaction yaitu abnormal return, kebocoran informasi, dan kepemilikan perusahaan yang terbukti secara signifikan dan berhubungan negatif terhadap nilai cumulative abnormal return (CAR) pada periode setelah peristiwa sebagai indikator dari fenomena overreaction., COVID-19 pandemic has a widespread impact on the capital market sector. The decline in stock prices occurred in Indonesian Islamic stocks at that time. Various information during the pandemic made investors overreact and led to market inefficiency. This study aims to identify the phenomenon of overreaction in Islamic stocks and analyze the factors that influence it. The approach used in this research is event study. The results show that overreaction occurred in winner stocks during the announcement of the first COVID-19 case in Indonesia (Event 1), while in the event of the issuance of the PEN program (Event 3), the arrival of the COVID-19 vaccine in Jakarta (Event 6), and the increase in The highest daily positive COVID-19 cases per August 2021 (Event 10) overreaction phenomenon occurred in winner-loser stocks. The results of cross sectional regression show that abnormal returns, leakage of information, and institutional ownership has a significant negative effect to cumulative abnormal return (CAR) in the period after the event as an indicator of the overreaction phenomenon.
Keyword: COVID-19, cross sectional regression, event, overreaction

Judul: Fenomena Overreaction Jangka Pendek Saham Syariah Indonesia selama Pandemi COVID-19
Abstrak: Pandemi COVID-19 merupakan peristiwa luar biasa yang tidak terduga. Krisis kesehatan tersebut berakibat pada perekonomian global tanpa terkecuali pasar saham syariah Indonesia. Goncangan pada pasar saham syariah menyebabkan ketidakpastian dan perubahan perilaku para investor yang berpotensi terjadi anomali overreaction. Penelitian ini bertujuan untuk menganalisis fenomena tersebut pada pasar saham syariah Indonesia. Metode analisis yang digunakan adalah uji beda dan cross sectional regression. Indeks yang digunakan adalah Jakarta Islamic Index (JII). Hasil penelitian menunjukkan bahwa peristiwa dilantiknya Joe Biden sebagai presiden Amerika Serikat selama Pandemi COVID-19 (Event 8) dan peristiwa kenaikan kasus kematian harian tertinggi akibat COVID-19 (Event 11) secara signifikan terjadi overreaction pada saham-saham kategori winner. Faktor yang memengaruhi overreaction tersebut adalah kapitalisasi pasar yang secara signifikan berpengaruh positif dengan overreaction. Selain itu, volume perdagangan secara signifikan berpengaruh negatif dengan terjadinya overreaction., The COVID-19 pandemic is an unexpected and extraordinary event. The health crisis has had an impact on the global economy without exception, including the Indonesian Sharia stock market. The shock in the Sharia stock markets has caused uncertainty and a change in the behavior of investors that could potentially lead to an anomaly of overreaction. The study aims to analyze the phenomenon in the Indonesian Sharia stock market. The analytical methods used are differential tests and cross-sectional regression. The index used is the Jakarta Islamic Index (JII). The results of the study showed that Joe Biden's appointment as president of the United States during the COVID-19 pandemic (Event 8) and the increase in daily deaths due to COVID-19 (Event 11) significantly overreacted to the winner category stocks. The factor that influences such overreactions is market capitalization, which significantly influences overreaction. Besides, trading volumes negatively influenced overreaction.
Keyword: COVID-19, Cross Sectional Regression, Islamic Stock Market, Overreaction

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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