7,245 research outputs found
Static spherically symmetric solution of the Einstein-aether theory
No full textBy using the Euler-Lagrange equations, we find a static spherically symmetric solution in the Einstein-aether theory with the coupling constants restricted. The solution is similar to the Reissner-Nordstrom solution in that it has an inner Cauchy horizon and an outer black hole event horizon. But a remarkable difference from the Reissner-Nordstrom solution is that it is not asymptotically flat but approaches a two-dimensional sphere. The resulting electric potential is regular in the whole spacetime except for the curvature singularity. On the other hand, the magnetic potential is divergent on both the Cauchy horizon and the outer event horizon
A study of the modern Chinese novel, Gao Yubao and its author Gao Yubao
No full textGao Yubao, a soldier in the Chinese People's Liberation Army, was nearly illiterate when he began to write his autobiographical novel, Gao Yubao, in 1949. The PLA's literary branch helped him finish the novel and after its publication Gao and his struggle to become literate by writing a novel served as an inspiration for others striving for education. Gao Yubao was republished several times up until as late as the 1970's and each time it was republished it was revised. This paper traces the history of the novel Gao Yubao and its author with special attention being given to comparing the changes made in the various editions of the novel. The conflicts between amateurism and professionalism and between fact and romanticization and those conflicts inherent in the constant revisings demanded of an already revised work are shown to be unresolvable because of the nature of contemporary Chinese literature.Arts, Faculty ofAsian Studies, Department ofGraduat
Cyclic universe due to phantom and quintessence
No full textWe explore a cyclic universe due to phantom and quintessence fields. We find that, in every cycle of the evolution of the universe, the phantom dominates the cosmic early history and quintessence dominates the cosmic far future. In this model of universe, there are infinite cycles of expansion and contraction. Different from the inflationary universe, the corresponding cosmic space-time is geodesically complete and quantum stable. But similar to the Cyclic Model, the flatness problem, the horizon problem and the large scale structure of the universe can be explained in this cyclic universe
Human activity has increasingly affected recent carbon accumulation in Zhanjiang mangrove wetland, South China
No full textSummary: Mangrove wetlands are an important component of blue carbon (C) ecosystems, although the anthropogenic impact on organic C accumulation rate (OCAR) in mangrove wetlands is not yet clear. Three sediment cores were collected from Zhanjiang Gaoqiao Mangrove Reserve in Southern China, dated by 210Pb and 137Cs, and physico-chemical parameters measured. Results show that the OCARs in mangroves and grasslands have significantly increased by 4.4 and 1.3 times, respectively, since 1950, which is consistent with the transformation of organic C sources and the increase of sedimentation rate. This increment is due to increased soil erosion and nutrient enrichment caused by land use change and the discharge of fertilizer runoff and aquaculture wastewater. This study provides clear evidence for understanding the changes in organic C accumulation processes during the Anthropocene and is conducive to promoting the realization of C peak and neutrality targets
Accommodating Nomocharis in Lilium (Liliaceae)
No full textControversy regarding the status of the genus Nomocharis Franchet (1889: 113) has been undergoing since its recognition by Franchet (1889). Recent molecular studies (Nishikawa et al. 1999, Hayashi & Kawano 2000, Nishikawa et al. 2001, Ronsted et al. 2005, Peruzzi et al. 2009) have resolved Nomocharis as being nested within Lilium Linaeus (1753: 302). Results of our own previous studies (Gao et al. 2012, Gao et al. 2013a, Gao et al. 2013b), with expanded sampling of species of Nomocharis have been congruent with those of previous studies by others. Thus recognition of Nomocharis would render Lilium paraphyletic. We prefer to recognize a monophyletic Lilium here, although paraphyletic groups are sometimes advocated in literature (e.g., Brummitt, 2014; Ehrendorfer & Barfuss, 2014; George, 2014; Horandl, 2014; Stuessy & Horandl, 2014; Stuessy et al., 2014). Most recently, we proposed that the morphological divergence between Nomocharis and Lilium was the result of habitat specialization (Gao et al. 2015). The extensive introgression caused by hybridization within Lilium and Nomocharis (Gao et al. 2013a, 2015) supports a single-genus concept
Remote estimation of chlorophyll a concentrations over a wide range of optical conditions based on water classification from VIIRS observations
No full textThe accurate estimate of surface chlorophyll a concentrations (Chla) by remote sensing presents a number of challenges where inherent and apparent optical properties have significant spatial or temporal variability. Indeed, Chla algorithms for Case 2 waters are often lake or region specific, and they are usually highly sensitive to changes in the dominant chromophoric constituents. This study develops and validates an absorption-specific approach to estimating Chla across an optically heterogeneous dataset. The approach is based on the classification of the optically dominant constituent. We tested this approach with in situ data from Taihu Lake, Poyang Lake, Chaohu Lake, Shitoukoumen Reservoir, Pearl River Estuary and Daya Bay as well as using HydroLight simulated data. The results show an improved performance when compared to most single Chla algorithms. We validated the approach with data from the Visible Infrared Imager Radiometer Suite (VIIRS). Results showed that this absorption-specific approach provided good Chla estimates over clear to very turbid waters with a wide range of optical conditions (R-2 = 0.76, r(RMSE) = 35%, n = 230, p < 0.01)
An absorption-specific approach to examining dynamics of particulate organic carbon from VIIRS observations in inland and coastal waters
No full textAn absorption-based approach was used to determine surface particulate organic carbon (POC) concentrations in both inland and coastal waters. The improved performance of this approach was based on the specification of local POC absorption characteristics based on dominant POC sources; phytoplankton or detritus based. This specification was made using a new POC-Index (PI), developed and tested across a range of POC (300-10,000 mg/m(3)) conditions in temporally and spatially heterogeneous inland and coastal waterbodies. The POC model was based on remote sensing reflectance (R-rs, sr(-1)) in four wavebands: R-rs(751), R-rs(488) and R-rs(R/G), where R is the red band [R-rs(672)] for detritus dominated waters and G is the green band [R-rs(555)] in the phytoplankton dominated waters. The model provided a high R-2 (0.74) and relatively low r(RMSE) (42.0%, N = 136, p < 0.01). Validation with independent datasets from Chaohu Lake and the Yangtze River Estuary produced a larger positive bias (R-2 = 0.59, r(RMSE) = 83%, delta = 634 mg/m(3), S = 0.63, I = 1439 mg/m(3)); nevertheless, the bias was reduced when tuned with local data (R-2 = 0.80, r(RMSE) = 45%, delta = 72 mg/m(3), S = 0.81, I = 327 mg/m(3)). Additionally, HydroLight simulations presented an independent correlation between PI and CDOM conditions and reasonable POC estimates from the new approach developed in this study. The approach was tested using data from Visible Infrared Imaging Radiometer Suite (VIIRS) in a range of optically complex conditions to quantify carbon dynamics. We indicate the advantages and challenges of using this approach in ecosystems where multiple organic carbon sources are present
Three thousand years of Hg pollution recorded in mangrove wetland sediments from South China
No full textMercury (Hg) is known to affect aquatic, terrestrial ecosystems as well as human health, through biomagnification. Mangrove wetlands are potential Hg sinks because of their low tidal velocity, fast sedimentation rate, strong reducing condition and high organic matter content. The spatial and temporal distribution of Hg has been a hot topic of recent studies in mangrove wetlands. In this study, we investigated Hg concentration, accumulation rate and isotopes to reconstruct the Hg pollution history and to differentiate its potential sources in the Gaoqiao mangrove wetland (Guangdong province), which is part of the largest mangrove area in China. We reconstructed a first, continuous, high-resolution Hg pollution history over the last 3000 years in South China. Our findings show that mangrove wetland sediments are more enriched in Hg than the adjacent grasslands. The increased Hg concentration and δ202Hg in recent sediments mirror the enhanced anthropogenic impacts; Hg concentrations in areas with high levels of anthropogenic disturbance are up to 5× higher than the average background value (9.9 ± 1.2 μg kg−1). Compared to mangroves in coastal areas of South China and around the world, the Hg concentration in Gaoqiao is much lower. The significant increase of Hg since the 1950s and the major Hg peak since the 1980s were the evidence of the human activities influences and indicated the possible start date of Anthropocene. After 2007 CE, a decline in Hg pollution occurs due to the effective implementation of the mangrove protection policy. Three potential sources were identified by the Hg isotope traces including urban gaseous Hg, industrial Hg, and regional soil and leaf litter Hg input
Adversarial Attacks against the Perception System of Autonomous Vehicles
No full textThe rapid advancement in autonomous driving technology underscores the importance of studying the fragility of perception systems in autonomous vehicles, particularly due to their profound impact on public transportation safety. These systems are of paramount importance due to their direct impact on the lives of passengers and pedestrians. Additionally, their reliability can be easily compromised given the complexity and unpredictability of driving environments. However, current research and existing regulations often fail to adequately address the adversarial robustness of autonomous vehicle perception systems. This thesis delves into the adversarial robustness of camera-based perception systems of autonomous vehicles. Our research concentrates on developing and implementing evasion attacks that use black-box gradient estimation, as well as physical attacks in traffic sign detection and classification systems. Our findings indicate that even minor perturbations can impact the accuracy of these systems, leading to detection and classification errors. This finding highlights a critical vulnerability in the perception system's robustness against adversarial attacks. Moreover, the study extends to assess the transferability of adversarial examples across diverse perception models. Our results also expose significant gaps in the current regulatory frameworks of autonomous vehicles, necessitating the establishment of more rigorous and comprehensive safety standards.https://github.com/yuxing-gao/adversarial-attack-traffic-sign-detectionMechanical Engineering | Systems and Contro
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