A wide variety of astrophysical and cosmological sources are expected to contribute to a stochastic gravitational-wave background. Following the observations of GW150914 and GW151226, the rate and mass of coalescing binary black holes appear to be greater than many previous expectations. As a result, the stochastic background from unresolved compact binary coalescences is expected to be particularly loud. We perform a search for the isotropic stochastic gravitational-wave background using data from Advanced Laser Interferometer Gravitational Wave Observatory’s (aLIGO) first observing run. The data display no evidence of a stochastic gravitational-wave signal. We constrain the dimensionless energy density of gravitational waves to be ${\Omega }_0<1.7\times {10}^{-7}$ with 95% confidence, assuming a flat energy density spectrum in the most sensitive part of the LIGO band (20–86 Hz). This is a factor of $\sim 33$ times more sensitive than previous measurements. We also constrain arbitrary power-law spectra. Finally, we investigate the implications of this search for the background of binary black holes using an astrophysical model for the background.

It is well known that global climate change causes an increase in forest fire frequency and severity. Thus, understanding fire dynamics is necessary to comprehend the mitigation of the negative effects of forest fires. Our objective was to inform how fire spreads in a simulated two-species forest with varying wind strengths. The forest in this study was comprised of two different tree species with varying probabilities of transferring fire that was randomly distributed in space at densities (Ctot) ranging from 0.0 (low) to 1.0 (high). We studied the distribution pattern of burnt trees by using local rules of the two-dimensional model. This model incorporated wind blowing from south to north with strength (Pw) ranging from 0.0 (low) to 1.0 (high). Simulation results showed that when Ctot > 0.45 the fire covered the entire forest, but when Ctot ≤ 0.45 the fire did not spread. The wind effect on the variation of the amount of the burnt tree was maximized at the critical density and dramatically decreased with increasing Ctot. Additionally, we found that the term of Ctot and Pw plays an important role in determining the distribution.

In this paper, we introduce a brief history of gravitational-wave detection experiments conducted by scientists over the last 55 years to detect graviational waves experimentally based on Einstein's theoretical prediction in 1916 and Weber's pioneering challenges in the 1960s. In particular, we describe both the status of the advanced LIGO (Laser Interferometer Gravitational-wave Observatory) recently developed and the reason the LIGO project may be the most promising candidate among gravitational-wave detectors after the Weber's bar detector. Furthermore, we present various models of next-generation gravitational-wave detectors and the research status of the Korean Gravitational Wave Group (KGWG).

The first historical direct observation of gravitational waves (GW150914) was accomplished by the Laser Interferometer Gravitational-wave Observatory (LIGO) on September 14, 2015. In this paper, we overview the observation of GW150914 and its data analysis including a validation of the detector's status around the arrival time of the event. We introduce two independent searches for transient gravitational waves and their results. We also present the contributions of the Korean Gravitational Wave Group (KGWG) to various aspects of the data analysis and the detector characterization within the LIGO Scientific Collaboration (LSC) and the Kamioka Gravitational-wave Observatory (KAGRA).