Reduction Arguments for Geometric Inequalities Associated With Asymptotically Hyperboloidal Slices

We consider several geometric inequalities in general relativity involving mass, area, charge, and angular momentum for asymptotically hyperboloidal initial data. We show how to reduce each one to the known maximal (or time symmetric) case in the asymptotically flat setting, whenever a geometrically motivated system of elliptic equations admits a solution.Comment: 30 pages; final versio

Spatiotemporal approach for estimating potential CO2 sequestration by reforestation in the Korean Peninsula

A forest is one of the carbon sinks in the terrestrial ecosystem; it is a major target for securing CO2 sequestration to achieve carbon neutrality. Reforestation is a forest management method that could attain carbon fixation and forest degradation recovery at the same time, but quantitative research has not been actively conducted. The purpose of this study is to identify the target areas for reforestation through changes in land cover in the Korean Peninsula and to quantify the potential CO2 sequestration effect of reforestation. According to the land cover change through satellite imagery, the area of settlements in the Republic of Korea (ROK) was the most dominant (+3,371 km2), and the main change occurred from cropland to settlements. The forest area increased by +1,544 km2 from 68,264 km2 in the 1980s to 69,809 km2 in the late 2010s. The forest decreased by 7,526 km2, accounting for 5.68% of the entire land area of the Democratic People's Republic of Korea (DPRK), and cropland increased by 5,222 km2 which is 5.12%. Assuming that the target of reforestation is an area whose land cover was a forest in the past and then converted to cropland, wetland, or bare ground, the area of the target decreased as the reference period was applied more recently. As a result of comparing the late 2000s to the late 2010s, the ROK's annual net carbon sequestration due to reforestation is predicted to be 10,833,600 Mg CO2 yr−1 in 2050 and 20,919,200 Mg CO2 yr−1 in 2070. In the DPRK, 14,236,800 Mg CO2 yr−1 in 2050 and 27,490,400 Mg CO2 yr−1 in 2070 were predicted. Reforestation in the Korean Peninsula was analyzed to have sufficient potential to secure a carbon sink, and the DPRK in particular was analyzed to be able to play a role in overseas reforestation

Hydrological response of dry Afromontane forest to changes in land use and land cover in northern Ethiopia

This study analyzes the impact of land use/land cover (LULC) changes on the hydrology of the dry Afromontane forest landscape in northern Ethiopia. Landsat satellite images of thematic mapper (TM) (1986), TM (2001), and Operational Land Imager (OLI) (2018) were employed to assess LULC. All of the images were classified while using the maximum likelihood image classification technique, and the changes were assessed by post-classification comparison. Seven LULC classes were defined with an overall accuracy 83-90% and a Kappa coefficient of 0.82-0.92. The classification result for 1986 revealed dominance of shrublands (48.5%), followed by cultivated land (42%). Between 1986 and 2018, cultivated land became the dominant (39.6%) LULC type, accompanied by a decrease in shrubland to 32.2%, as well as increases in forestland (from 4.8% to 21.4%) and bare land (from 0% to 0.96%). The soil conservation systems curve number model (SCS-CN) was consequently employed to simulate forest hydrological response to climatic variations and land-cover changes during three selected years. The observed changes in direct surface runoff, the runoff coefficient, and storage capacity of the soil were partially linked to the changes in LULC that were associated with expanding bare land and built-up areas. This change in land use aggravates the runoff potential of the study area by 31.6 mm per year on average. Runoff coefficients ranged from 25.3% to 47.2% with varied storm rainfall intensities of 26.1-45.4 mm/ha. The temporal variability of climate change and potential evapotranspiration increased by 1% during 1981-2018. The observed rainfall and modelled runoff showed a strong positive correlation (R-2 = 0.78; p < 0.001). Regression analysis between runoff and rainfall intensity indicates their high and significant correlation (R-2 = 0.89; p < 0.0001). Changes were also common along the slope gradient and agro-ecological zones at varying proportions. The observed changes in land degradation and surface runoff are highly linked to the change in LULC. Further study is suggested on climate scenario-based modeling of hydrological processes that are related to land use changes to understand the hydrological variability of the dry Afromontane forest ecosystems

Red supergiants in M31: the Humphreys-Davidson limit at high metallicity

The empirical upper limit to red supergiant (RSG) luminosity, known as the Humphreys–Davidson (HD) limit, has been commonly explained as being caused by the stripping of stellar envelopes by metallicity-dependent line-driven winds. As such, the theoretical expectation is that the HD limit should be higher at lower metallicity, where weaker mass-loss rates mean that higher initial masses are required for an envelope to be stripped. In this paper, we test this prediction by measuring the luminosity function of RSGs in M31 and comparing it to those in the LMC and SMC. We find that log (Lmax/L⊙) = 5.53 ± 0.03 in M31 (Z ≳ Z⊙), consistent with the limit found for both the LMC (Z ∼ 0.5 Z⊙) and SMC (Z ∼ 0.25 Z⊙), while the RSG luminosity distributions in these three galaxies are consistent to within 1σ. We therefore find no evidence for a metallicity dependence on both the HD limit and the RSG luminosity function, and conclude that line-driven winds on the main sequence are not the cause of the HD limit