arXiv subjects

Kota Ogasawara

Publications and source records attributed to Kota Ogasawara.

At least 19 recordsLinked to original sources

arXiv2026

Urban Reconstruction and Population Redistribution: Evidence from Tokyo after the Great Kanto Earthquake

This study examines the impact of the 1923 Great Kanto Earthquake on population distribution within Tokyo City. The earthquake triggered massive fires that devastated nearly half of the city, including much of its urban core. To investigate its consequences, I digitized systematic census statistics and conducted regression analyses using variation in fire damage across areas. The results show that land readjustment implemented as part of the reconstruction project reduced residential land area within the burned area, leading to higher unit rents. Although the total residential floor area eventually recovered through the construction of multi-story dwellings, the population of the burned area remained below its pre-earthquake level throughout the period examined. In addition, the zoning system established before the earthquake had little effect on population redistribution. These findings suggest that post-disaster population distribution was shaped primarily by market-based price adjustments rather than institutional regulations. The analysis further shows that rising rents reduced the number of kinship households while increasing incentives for workers to rent rooms as lodgers. The rent burden borne by lodgers, relative to that borne by landlords, was lower in the burned area, making housing sharing an effective response. Overall, the post-disaster population decline in the burned area reflected the net effect of two opposing forces: population loss driven by rising rents and population retention through increased housing sharing among worker households seeking to mitigate those rent increases.

econ.GN↗

arXiv2026

Technology, Institution, and Regional Growth: Evidence from Mineral Mining Industry in Industrializing Japan

Coal mining was an influential economic activity in interwar Japan. Initially, coal mines employed both men and women in the pits. However, the introduction of labor-saving technologies and the modernization of traditional extraction methods induced institutional change, manifested in the revision of labor regulations affecting female miners in the early 1930s. This dramatically changed the mining workplace, making skilled men the principal underground miners. This paper investigates the impact of coal mining on regional growth and assesses how institutional changes induced by the amended labor regulations affected this growth process. By linking the mines' location information with both registration- and census-based statistics, I find that coal mines led to remarkable population growth, and that fertility rates increased following the labor regulations that removed female miners from the workforce. While occupational hazards increased early-life mortality via the mortality selection mechanism, the effect of the regulations on mortality reduction remains unclear.

econ.GN↗

arXiv2026

Odd-parity ringdown gravitational waves of a spherically symmetric black hole with perfect fluid accretion

The ringdown waves from a black hole offer a clean probe of strong-field gravity, but a matter distribution that may be present around a realistic black hole renders the background spacetime dynamical and the ringdown frequencies time-dependent. We study the odd-parity ringdown of a Schwarzschild black hole that grows through the dilute, steady, spherically symmetric accretion of a perfect fluid. Working to first order in the accretion rate, we compute the ringdown waveform directly in the time domain on this dynamical background. Since the odd-parity matter perturbation decouples from the metric perturbation, the wave mode can be described by a purely tensorial mode on the accreting background. In particular, the ratio of the imaginary to the real part of the frequency cancels both the secular variation caused by the growth of the black hole and the redshift factor, so that its deviation from the Schwarzschild value purely reflects the surrounding environment. The time dependence of the frequency, on the other hand, reflects the accretion rate and allows us to define a second observable tied to it. We argue that measuring these observables across multiple modes may provide significant information to constrain the surrounding environment of the black hole.

gr-qc↗

arXiv2025

Risk-coping Behaviors in Metropolis: Evidence from Working-class Households in Prewar Tokyo

I analyze the risk-coping strategies of factory-worker households in early twentieth-century Tokyo. I digitized a unique daily longitudinal household budget survey conducted in Tsukishima, a representative manufacturing area, to examine how consumption was affected by idiosyncratic shocks. I find that although the households were vulnerable and their consumption levels were impacted by these shocks, the estimated income elasticity of indispensable consumption was relatively low in the short run. The results of the mechanism analysis suggest that credit purchases from local retailers helped smooth short-run consumption, highlighting the role of informal credit institutions in mitigating vulnerability among urban worker households.

econ.GN↗

arXiv2024

The Impacts of the Gender Imbalance on the Marriage Market: Evidence from World War II in Japan

This study uses the unprecedented changes in the sex ratio due to the losses of men during World War II to identify the impacts of the gender imbalance on marriage market outcomes in Japan. Using newly digitized census-based historical statistics, we find evidence that men have a stronger bargaining position in the marriage market than women do. Under the conditions of relative male scarcity, women are less likely to marry. Although the entry of younger cohorts with a natural gender balance into the marriage market attenuated its magnitude, this tendency persisted until the mid-1950s. Widowed women facing male scarcity are particularly unable to remarry. Our results suggest that reinstating military pensions in the early 1950s further reduced their incentive to remarry.

econ.GN↗

arXiv2024

New series expansion method for the periapsis shift

We propose a new series expansion method for the periapsis shift. The method formulates the periapsis shift in various spacetimes analytically without using special functions and provides simple and highly accurate approximate formulae. We derive new series representations for the periapsis shift in the Kerr and the Chazy-Curzon spacetimes by using the method, where the expansion parameter is defined as the eccentricity divided by the non-dimensional quantity that vanishes in the limit of the innermost stable circular orbit. That is to say, the expansion parameter denotes how eccentric the orbit is and how close it is to the innermost stable circular orbit. The smaller the eccentricity, the higher the accuracy of the formulae that are obtained by truncating the new series representations up to a finite number of terms. If the eccentricity is sufficiently small, the truncated new representations have higher accuracy than the post-Newtonian expansion formulae even in strong gravitational fields where the convergence of the post-Newtonian expansion formula is not guaranteed. On the other hand, even if the orbit is highly eccentric, the truncated new representations have comparable or higher accuracy than the post-Newtonian expansion formulae if the semi-major axis is sufficiently large. An exact formula for the periapsis shift of the quasi-circular orbit in the Chazy-Curzon spacetime is also obtained as a special case of the new series representation.

gr-qc↗

arXiv2024

Consumption smoothing in the working-class households of interwar Japan

I analyze factory worker households in the early 1920s in Osaka to examine idiosyncratic income shocks and consumption. Using the household-level monthly panel dataset, I find that while households could not fully cope with idiosyncratic income shocks at that time, they mitigated fluctuations in indispensable consumption during economic hardship. In terms of risk-coping mechanisms, I find suggestive evidence that savings institutions helped mitigate vulnerabilities and that both using borrowing institutions and adjusting labor supply served as risk-coping strategies among households with less savings.

econ.GN↗

arXiv2022

Pandemic Influenza and Gender Imbalance: Mortality Selection before Births

This study uses data from the 1918-1920 influenza pandemic in Japan along with newly digitized and complete census records on births and infant deaths to analyze mortality selection in utero. I find that fetal exposure to the influenza pandemic during the first trimester of the pregnancy decreases the proportion of males at birth. The results from mechanism analysis suggest that this decline in male births is associated with the deterioration of fetal and infant health. This result supports a wide range of existing literature on the long-run adverse effects of pandemic influenza.

stat.AP↗

arXiv2022

Photon escape in the extremal Kerr black hole spacetime

We consider necessary and sufficient conditions for photons emitted from an arbitrary spacetime position of the extremal Kerr black hole to escape to infinity. The radial equation of motion determines the necessary conditions for photons emitted from $r=r_*$ to escape to infinity, and the polar angle equation of motion further restricts the allowed region of photon motion. From these two conditions, we provide a method to visualize a two-dimensional photon impact parameter space that allows photons to escape to infinity, i.e., the escapable region. Finally, we completely identify the escapable region for the extremal Kerr black hole spacetime. This study has generalized our previous result [K.~Ogasawara and T.~Igata, Phys. Rev. D \textbf{103}, 044029 (2021)], which focused only on light sources near the horizon, to the classification covering light sources in the entire region.

gr-qc↗

arXiv2021

Persistence of Natural Disasters on Children's Health: Evidence from the Great Kanto Earthquake of 1923

This study uses a catastrophic earthquake in 1923 to analyse the long-term effects of a natural disaster on children's health. I find that fetal exposure to Japan's Great Kanto Earthquake had stunting effects on girls in the devastated area. Disaster relief spending helped remediate stunting among boys by late primary school age, whereas it did not ameliorate girls' stunting, suggesting a prenatal selection mechanism and compensating investment after birth. While the maternal mental stress via the fear of vibrations and anticipation of future aftershocks played a role in the adverse health effects, the maternal nutritional stress via physical disruption also enhanced those effects.

stat.AP↗

arXiv2021

Photon emission from inside the innermost stable circular orbit

We consider a situation where a light source orbiting the innermost stable circular orbit (ISCO) of the Kerr black hole is gently falling from the marginally stable orbit due to an infinitesimal perturbation. Assuming that the light source emits photons isotropically, we show that the last radius at which more than 50\% of emitted photons can escape to infinity is approximately halfway between the ISCO radius and the event horizon radius. To evaluate them, we determine emitter orbits from the vicinity of the ISCO, which are uniquely specified for each black hole spin, and identify the conditions for a photon to escape from any point on the equatorial plane of the Kerr spacetime to infinity by specifying regions in the two-dimensional photon impact parameter space completely. We further show that the proper motion of the emitter affects the photon escape probability and blueshifts the energy of emitted photons.

gr-qc↗

arXiv2021

Complete classification of photon escape in the Kerr black hole spacetime

We consider necessary and sufficient conditions for photons emitted from the vicinity of a Kerr black hole horizon to escape to infinity. The radial equation of motion determines necessary conditions for photons to reach infinity, and the polar angle equation of motion further restricts the allowed region of photon motion. Unlike emission from the equatorial plane, the latter restrictions are crucial for photon escape when the initial polar angle of the emission point is arbitrary. We provide a visualization tool to analyze these two conditions and demonstrate a procedure for revealing photon escape. Finally, we completely identify the two-dimensional impact parameter space in which photons can escape.

gr-qc↗

arXiv2020

Observability of the innermost stable circular orbit in a near-extremal Kerr black hole

We consider the escape probability of a photon emitted from the innermost stable circular orbit (ISCO) of a rapidly rotating black hole. As an isotropically emitting light source on a circular orbit reduces its orbital radius, the escape probability of a photon emitted from it decreases monotonically. The escape probability evaluated at the ISCO also decreases monotonically as the black hole spin increases. When the dimensionless Kerr parameter $a$ is at the Thorne limit $a=0.998$, the escape probability from the ISCO is $58.8\%$. In the extremal case $a=1$, even if the orbital radius of the light source is arbitrarily close to the ISCO radius, which coincides with the horizon radius, the escape probability remains at $54.6\%$. We also show that such photons that have escaped from the vicinity of the horizon reach infinity with sufficient energy to be potentially observed because Doppler blueshift due to relativistic beaming can overcome the gravitational redshift. Our findings indicate that signs of the near-horizon physics of a rapidly rotating black hole will be detectable on the edge of its shadow.

astro-ph.HE↗

arXiv2020

Small Area Estimation with Spatially Varying Natural Exponential Families

Two-stage hierarchical models have been widely used in small area estimation to produce indirect estimates of areal means. When the areas are treated exchangeably and the model parameters are assumed to be the same over all areas, we might lose the efficiency in the presence of spatial heterogeneity. To overcome this problem, we consider a two-stage area-level model based on natural exponential family with spatially varying model parameters. We employ geographically weighted regression approach to estimating the varying parameters and suggest a new empirical Bayes estimator of the areal mean. We also discuss some related problems, including the mean squared error estimation, benchmarked estimation, and estimation in non-sampled areas. The performance of the proposed method is evaluated through simulations and applications to two data sets.

stat.ME↗

arXiv2019

Particulate Air Pollution, Birth Outcomes, and Infant Mortality: Evidence from Japan's Automobile Emission Control Law of 1992

This study investigates the impacts of the Automobile NOx Law of 1992 on ambient air pollutants and fetal and infant health outcomes in Japan. Using panel data taken from more than 1,500 monitoring stations between 1987 and 1997, we find that NOx and SO2 levels reduced by 87% and 52%, respectively in regulated areas following the 1992 regulation. In addition, using a municipal-level Vital Statistics panel dataset and adopting the regression differences-in-differences method, we find that the enactment of the regulation explained most of the improvements in the fetal death rate between 1991 and 1993. This study is the first to provide evidence on the positive impacts of this large-scale automobile regulation policy on fetal health.

econ.GN↗

arXiv2019

Escape probability of a photon emitted near the black hole horizon

We investigate the escape of photons from the vicinity of the horizon to infinity in the Kerr-Newmann black hole spacetime. We assume that a light source is at rest in a locally nonrotating frame and photons are emitted isotropically. Then, we evaluate the escape probability of the emitted photons. The main result of this paper is the following. If the black hole is extremal with the nondimensional spin parameter $a_*> 1/2$, however close to the horizon the light source would be, the escape probability remains nonzero. The near-horizon limit value of the escape probability is a monotonically increasing function of $a_*$ and takes a maximum $\sim$29.1\% at $a_*=1$, i.e., for the extremal Kerr case. On the other hand, if the black hole is extremal with $0\leq a_*\leq 1/2$ or if the black hole is subextremal, the near-horizon limit value is zero.

gr-qc↗

arXiv2019

Chain effects of clean water: The Mills-Reincke phenomenon in early twentieth-century Japan

This study explores the validity of chain effects of clean water, which are known as the "Mills-Reincke phenomenon," in early twentieth-century Japan. Recent studies have reported that water purifications systems are responsible for huge contributions to human capital. Although some studies have investigated the instantaneous effects of water-supply systems in pre-war Japan, little is known about the chain effects of these systems. By analyzing city-level cause-specific mortality data from 1922-1940, we find that a decline in typhoid deaths by one per 1,000 people decreased the risk of death due to non-waterborne diseases such as tuberculosis and pneumonia by 0.742-2.942 per 1,000 people. Our finding suggests that the observed Mills-Reincke phenomenon could have resulted in the relatively rapid decline in the mortality rate in early twentieth-century Japan.

stat.AP↗

arXiv2019

Effect of the self-gravity of shells on a high energy collision in a rotating Bañados-Teitelboim-Zanelli spacetime

We consider a collision of two dust thin shells with a high center-of-mass (CM) energy including their self-gravity in a Bañados-Teitelboim-Zanelli (BTZ) spacetime. The shells divide the BTZ spacetime into three domains and the domains are matched by the Darmois-Israel junction conditions. We treat only the collision of two shells which corotate with a background BTZ spacetime because of the junction conditions. The counterpart of the corotating shell collision is a collision of two particles with vanishing angular momenta. We compare the dust thin shell collision and the particle collision in order to investigate the effects of the self-gravity of colliding objects on the high CM energy collision. We show that the self-gravity of the shells affects the position of an event horizon and it covers the high-energy collisional event. Therefore, we conclude that the self-gravity of colliding objects suppresses its CM energy and that any observer who stands outside of the event horizon cannot observe the collision with an arbitrary high CM energy.

gr-qc↗