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 di Indonesia terhadap COVID-19
Abstrak: COVID-19 merupakan peristiwa yang menimbulkan dampak buruk di berbagai sektor salah satunya adalah sektor pasar modal. Kondisi ketidakpastian yang tinggi akibat mewabahnya COVID-19 menyebabkan investor bereaksi terhadap peristiwa tersebut sehingga dapat menimbulkan fenomena overreaction. Peristiwa yang diambil dalam sampel penelitian ini sejumlah tujuh peristiwa terkait COVID-19. Penelitian ini bertujuan untuk menganalisis fenomena overreaction pada saham syariah dan faktor yang memengaruhinya dengan menggunakan metode uji beda dan cross sectional regression. Hasil penelitian menunjukkan bahwa Pengumuman transmisi COVID-19 dan lockdown (Event 2) menyebabkan overreaction pada saham winner. Fenomena overreaction saham loser disebabkan oleh pengumuman stimulus fiskal Amerika Serikat (Event 5) dan pengumuman PSBB (Event 6). Peristiwa pengumuman new normal (Event 7) menyebabkan saham winner maupun loser mengalami overreaction. Faktor yang memengaruhi fenomena overreaction pada peristiwa tersebut terbukti secara signifikan dan berhubungan negatif adalah leverage dan kapitalisasi pasar, sedangkan volume perdagangan secara signifikan memengaruhi dan memiliki hubungan positif dengan fenomena overreaction., COVID-19 is an event that has harmed various sectors, one of which is the capital market sector. The high uncertainty caused by the COVID-19 outbreak caused investors to react to this event, which could cause an overreaction phenomenon. The events taken in this study sample are seven events related to COVID-19. This study aims to analyze the phenomenon of overreaction in Islamic stocks and the factors that influence the phenomenon of overreaction by using the two-sample difference test method and cross-sectional regression. The results showed that the announcement of COVID-19 transmission and lockdown (Event 2) caused overreaction in winner stocks. The phenomenon of loser stock overreaction was caused by the announcement of the United States fiscal stimulus (Event 5) and the announcement of the PSBB (Event 6). The new normal announcement event (Event 7) caused Islamic stocks both winner and loser to experience overreaction. The factors that influence the overreaction phenomenon in this event are proven to be significantly and negatively influenced by leverage and market capitalization, while trading volume had a significant effect and positively influence the overreaction phenomenon.
Keyword: COVID-19, cross sectional regression, 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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