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Spacetime singularity has always been of interest since the proof of the Penrose-Hawking singularity theorem. Naked singularity naturally emerges from reasonable initial conditions in the collapsing process. A recent interesting approach in black hole information problem implies that we need a firewall to break the surplus entanglements among the Hawking photons. Classically, the firewall becomes a naked singularity. We find some vacuum analytical solutions in R n -gravity of the firewall-type and use these solutions as concrete models to study the naked singularities. By using standard quantum theory, we investigate the Hawking radiation emitted from the black holes with naked singularities. Here we show that the singularity itself does not destroy information. A unitary quantum theory works well around a firewall-type singularity. We discuss the validity of our result in general relativity. Further our result demonstrates that the temperature of the Hawking radiation still can be expressed in the form of the surface gravity divided by 2 π . This indicates that a naked singularity may not compromise the Hakwing evaporation process.

Exact solutions of spherically symmetric black hole and gravitational wave are explored in f ( R ) gravity in arbitrary dimension. We find two exact solutions for the radiation and absorption of null dust. In the framework of general relativity, the Birkhoff theorem strictly forbids the existence of spherical gravitational waves in vacuum space. We find spherical non-perturbative gravitational waves, which are shear-free, twist-free, but expanding.

China has been experiencing fine particle (i.e., aerodynamic diameters ≤ 2.5 μm; PM2.5) pollution and acid rain in recent decades, which exert adverse impacts on human health and the ecosystem. Recently, ammonia (i.e., NH₃) emission reduction has been proposed as a strategic option to mitigate haze pollution. However, atmospheric NH₃ is also closely bound to nitrogen deposition and acid rain, and comprehensive impacts of NH₃ emission control are still poorly understood in China. In this study, by integrating a chemical transport model with a high-resolution NH₃ emission inventory, we find that NH₃ emission abatement can mitigate PM2.5 pollution and nitrogen deposition but would worsen acid rain in China. Quantitatively, a 50% reduction in NH₃ emissions achievable by improving agricultural management, along with a targeted emission reduction (15%) for sulfur dioxide and nitrogen oxides, can alleviate PM2.5 pollution by 11−17% primarily by suppressing ammonium nitrate formation. Meanwhile, nitrogen deposition is estimated to decrease by 34%, with the area exceeding the critical load shrinking from 17% to 9% of China’s terrestrial land. Nevertheless, this NH₃ reduction would significantly aggravate precipitation acidification, with a decrease of as much as 1.0 unit in rainfall pH and a corresponding substantial increase in areas with heavy acid rain. An economic evaluation demonstrates that the worsened acid rain would partly offset the total economic benefit from improved air quality and less nitrogen deposition. After considering the costs of abatement options, we propose a region-specific strategy for multipollutant controls that will benefit human and ecosystem health.

Machine learning is one of the most widely studied and applied technologies, but it is itself vulnerable to attack and its algorithms have the risk of privacy leakage. In this article, through the experts currently popular speech recognition scene, reveals how to build the antagonism against data, make its differences with the source data is subtle, so much so that humans can’t through sensory recognition, and machine learning model can accept and the classification of making the wrong decision, at the same time made attack, finally prospects the study model to research the development and application of security and privacy protection.

We find a novel characteristic for chaotic motion by introducing Shannon entropy for periodic orbits, quasiperiodic orbits, and chaotic orbits. We compare our approach with the previous methods including Poincaré section, Lyapunov exponent, fast Lyapunov indicator, recurrence plots (Rps), and fast Fourier transform (FFT) for orbits around black holes immersed in magnetic fields, and show that they agree with each other quite well. The approach of Shannon entropy is intuitively clear, and theoretically reasonable since it becomes larger and larger from a periodic orbit to chaotic orbit. We demonstrate that Shannon entropy can be a powerful probe to distinguish between chaotic and regular orbits in different spacetimes, and reversely may lead to a new route to define the entropy for a single orbit in phase space, and to find more fundamental relations between thermodynamics and dynamics. Furthermore, we find that the fluctuations of entropy of chaotic orbits are stronger than those of order orbits.

Extreme sea levels (ESLs) induce significant risks to Hong Kong. With climate change, the risks will be amplified, while existing studies have not provided fine-grained simulations of Hong Kong’s future ESL exposure and its socio-economic risks. Employing a GIS-based coastal flood inundation model, this research integrates a high-resolution Digital Terrain Model (DTM) with datasets of ESL forecasts, demography, economy, infrastructure, and land use to estimate the future ESL risks posed on Hong Kong for 2050 and 2100 under two Representative Concentration Pathways (RCPs): RCP4.5 and RCP8.5. The projections indicate that, under RCP4.5, over 27.66% of the population and 39.52% of the Gross Domestic Product (GDP) will be exposed to ESL after 2050. Under RCP8.5 scenario, the exposed population may surpass 31.21%, with economic exposure estimated at 40.98% of GDP after 2050. Under both RCPs, Hong Kong’s ESL-threatened area may range from 8.23 to 11.41%, exposing over 16.09% of the infrastructure to ESL after 2050. Regions in the northwestern Yuen Long, Tuen Mun River Estuary, Rambler Channel coast, Victoria Harbor coast, Shing Mun River, and Tai Po Waterfront have particularly high ESL risks. The findings highlight the need for resilient infrastructure to counteract the long-term risks ESL poses in Hong Kong.

The identification of species within an ecosystem plays a key role in formulating an inventory for use in the development of conservation management plans. The classification of mangrove species typically involves intensive field surveys, whereas remote sensing techniques represent a cost-efficient means of mapping and monitoring mangrove forests at large scales. However, the coarse spectral resolution of remote sensing technology has up until recently restricted the ability to identify individual species. The more recent development of very high-resolution spatial optical remote sensing sensors and techniques has thus provided new opportunities for the accurate mapping of species within mangrove forests over large areas. When dealing with the complex problems associated with discriminating among species, classifier performance could be enhanced through the adoption of more intrinsic features; such as textural and differential spectral features. This study explored the effectiveness of textural and differential spectral features in mapping mangrove inter-species obtained from WorldView-3 high-spatial-resolution imagery for mangrove species in Hong Kong. Due to the different arrangement of leaves, the branch density, and the average height and size of plants, we found that the differential spectral features could aid in reducing inner-species variability and increasing intra-species separation. Using a combination of textural and differential spectral features thus represents a promising tool for discriminating among mangrove species. Experimental results suggest that combining these features can greatly improve mapping accuracy, thereby providing more reliable mapping results.

Wave propagations in the presence of black holes is a significant problem both in theoretical and observational aspects, especially after the discovery of gravitational wave and confirmation of black holes. We study the scattering of massless scalar field by a charged dilatonic black hole in frame of full wave theory. We apply partial wave method to obtain the scattering cross sections of the scalar field, and investigate how the black hole charge affects the scalar scattering cross sections. Furthermore, we investigate the Regge pole approach of the scattering cross section of the dilatonic black hole. We find that in order to obtain results at the same precision, we need more Regge poles as the black hole charge increases. We compare the results in the full wave theory and results in the classical geodesic scattering and the semi-classical glory approximations, and demonstrate the improvements and power of our approach.

A bstract Spherical gravitational wave is strictly forbidden in vacuum space in frame of general relativity by the Birkhoff theorem. We prove that spherical gravitational waves do exist in non-linear massive gravity, and find the exact solution with a special singular reference metric. Further more, we find exact gravitational wave solution with a singular string by meticulous studies of familiar equation, in which the horizon becomes non-compact. We analyze the properties of the congruence of graviton rays of these wave solution. We clarify subtle points of dispersion relation, velocity and mass of graviton in massive gravity with linear perturbations. We find that the graviton ray can be null in massive gravity by considering full back reaction of the massive gravitational waves to the metric. We demonstrate that massive gravity has deep and fundamental discrepancy from general relativity, for whatever a tiny mass of the graviton.

A bstract Strong self-gravitational fields enable the realization of macroscopic odd-parity quantum objects. Using ray-tracing methods, we systematically analyze the dynamics of photons and the shadow features of rotating black holes with parity-odd scalar hair and contrast them with those of Kerr black holes. Our results demonstrate measurable distinctions between scalar-haired black hole shadows and their Kerr counterparts. Notably, even for tiny scalar charge and negligible scalar hair mass contributions, these differences remain quantitatively resolvable. In particular, one of the hairy black hole reported here lies within the Event Horizon Telescope observational uncertainties, probing the scalar masses of 1.02 × 10 − 20 eV with M87*. These findings may provide related theoretical benchmarks for future observational campaigns targeting scalar-field dark matter candidates through black hole shadow imaging.