The recent HAWC observations of a very-high-energy γ-ray halo around Geminga and Monogem indicate a very slow diffusion of cosmic rays that results in a tiny contribution of positrons from these two ...pulsars to the local flux. This makes the cosmic positron excess anomaly observed by PAMELA and AMS-02 even more puzzling. However, from the boron-to-carbon ratio data one can infer that the average diffusion coefficient in the Galaxy should be much larger. In this work we propose a two-zone diffusion model in which the diffusion is slow only in a small region around the source, outside of which the propagation is as fast as usual. We find that this scenario can naturally explain the positron excess data with parameters even more reasonable than those in the conventional one-zone diffusion model. The reason is that during the lifetime of Geminga (∼300 kyr), the electrons/positrons have propagated too far away with a fast diffusion and led to a low local flux. The slow-diffusion region in the two-zone model helps to confine the electrons/positrons for a long time and lead to an enhancement of the local flux. So under the constraint of the HAWC observations, pulsars are still the probable origin of the cosmic-ray positron excess.
Soil heavy metal pollution has been becoming serious and widespread in China. To date, there are few studies assessing the nationwide soil heavy metal pollution induced by industrial and agricultural ...activities in China. This review obtained heavy metal concentrations in soils of 402 industrial sites and 1041 agricultural sites in China throughout the document retrieval. Based on the database, this review assessed soil heavy metal concentration and estimated the ecological and health risks on a national scale. The results revealed that heavy metal pollution and associated risks posed by cadmium (Cd), lead (Pb) and arsenic (As) are more serious. Besides, heavy metal pollution and associated risks in industrial regions are severer than those in agricultural regions, meanwhile, those in southeast China are severer than those in northwest China. It is worth noting that children are more likely to be affected by heavy metal pollution than adults. Based on the assessment results, Cd, Pb and As are determined as the priority control heavy metals; mining areas are the priority control areas compared to other areas in industrial regions; food crop plantations are the priority control areas in agricultural regions; and children are determined as the priority protection population group. This paper provides a comprehensive ecological and health risk assessment on the heavy metals in soils in Chinese industrial and agricultural regions and thus provides insights for the policymakers regarding exposure reduction and management.
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•402 industrial and 1041 agricultural sites are reviewed.•Pollution and risks in industrial regions were severer than agricultural regions.•30% of industrial sites pose potential non-carcinogenic risk.•The majority of As carcinogenic risks are at a relatively unacceptable range.•The priority control components were identified.
In this work we use the newly reported boron-to-carbon ratio (B/C) from AMS-02 and the time-dependent proton fluxes from PAMELA and AMS-02 to constrain the source and propagation parameters of cosmic ...rays in the Milky Way. A linear correlation of the solar modulation parameter with solar activities is assumed to account for the time-varying cosmic ray fluxes. A comprehensive set of propagation models, with or without reacceleration or convection, has been discussed and compared. We find that only the models with reacceleration can self-consistently fit both the proton and B/C data. The rigidity dependence slope of the diffusion coefficient, δ, is found to be about 0.38–0.50 for the diffusion-reacceleration models. The plain diffusion and diffusion-convection models fit the data poorly. We compare different model predictions of the positron and antiproton fluxes with the data. We find that the diffusion-reacceleration models overproduce low energy positrons, while nonreacceleration models give better fit to the data. As for antiprotons, reacceleration models tend to underpredict low energy antiproton fluxes, unless a phenomenological modification of the velocity dependence of the diffusion coefficient is applied. Our results suggest that there could be important differences of the propagation for nuclei and leptons, in either the Milky Way or the solar heliosphere.
Controller placement is a key problem in software defined networks (SDNs). Previously, the solution to this problem only focused on propagation latency but ignored the load of controllers, which is a ...critical factor in real networks. In this letter, we define a capacitated controller placement problem (CCPP), taking into consideration the load of controllers, and introduce an efficient algorithm to solve the problem. The evaluation shows that the new strategy can significantly reduce the number of required controllers, reduce the load of the maximum-load controller, and reduce the radius stretches compared with the K-center strategy with dynamic controller provision or dynamic scheduling.
ABSTRACT
Geminga pulsar is surrounded by a multiTeV γ-ray halo radiated by the high-energy electrons and positrons accelerated by the central pulsar wind nebula (PWN). The angular profile of the ...γ-ray emission reported by High-Altitude Water Cherenkov Observatory indicates an anomalously slow diffusion for the cosmic-ray electrons and positrons in the halo region around Geminga. In the paper we study the possible mechanism for the origin of the slow diffusion. At first, we consider the self-generated Alfvén waves due to the streaming instability of the electrons and positrons released by Geminga. However, even considering a very optimistic scenario for the wave growth, we find this mechanism does not work to account for the extremely slow diffusion at the present day, if taking the proper motion of Geminga pulsar into account. The reason is straightforward as the PWN is too weak to generate enough high-energy electrons and positrons to stimulate strong turbulence at the late time. We then propose an assumption that the strong turbulence is generated by the shock wave of the parent supernova remnant (SNR) of Geminga. Geminga may still be inside the SNR, and we find that the SNR can provide enough energy to generate the slow-diffusion circumstance. The TeV haloes around PSR B0656+14, Vela X, and PSR J1826-1334 may also be explained under this assumption.
•A multi-year spatiotemporal machine learning model on ozone was established.•We reconstructed a high resolution ground ozone dataset from 2005 to 2017 in China.•External model testing R2 = 0.60–0.87 ...at the month level in different years.•We identified spatial hotspots and temporal trends of ozone pollution in China.•This study provides a good data source for ozone health effects studies in China.
In recent years, ground-level ozone has become a severe ambient pollutant in major urban areas of China, which has adverse impacts on population health. However, in-situ measurements of the ozone concentration before 2013 in China are quite scarce, which cannot facilitate the assessment of the long-term trends and effects of ozone pollution. In this study, we used daily maximum 8-hour average (MDA8) ozone observations from 2013 to 2017 combined with concurrent ozone retrievals, aerosol reanalysis, meteorological parameters, and land-use data to establish a nationwide MDA8 prediction model based on the eXtreme Gradient Boosting (XGBoost) algorithm. The model achieves high prediction accuracy compared with other studies, with R2 values for the by-year, site-based, and sample-based cross-validation (CV) schemes of 0.61, 0.64, and 0.78, respectively, at the daily level. External testing with regional measurements from 2005 to 2012 and nationwide data in 2018 have shown that the model is robust and reliable for historical data prediction, with external model testing R2 values ranging from 0.60 to 0.87 at the month level in different years. Using the final estimator, we obtained nationwide monthly mean ozone concentrations from 2005 to 2012 and daily MDA8 ozone concentrations from 2013 to 2017 at a resolution of 0.1° × 0.1°. According to the average number of days exceeding the standard and the average of the 90th percentile of the MDA8 ozone concentrations, the Beijing-Tianjin-Hebei (BTH), the Yangtze River Delta, the Pearl River Delta, the Jianghan Plain, the Sichuan Basin, and the Northeast Plain regions were identified as pollution hotspots. During the research period, the overall ozone levels fluctuated slightly, and their trends were not spatially continuous. There was a significant increasing trend in the BTH region by 1.37 (95% CI: 0.46,2.29) μg/m3/year between 2013 and 2017. In 2017, 26.24% of the population lived in areas exceeding the Chinese grade II national air quality standard, which shows that ozone pollution has posed an obvious threat to population health in China. Our products will provide reliable support for future long-term nationwide health impact studies and policy-making for pollution control and prevention.
China established ground PM2.5 monitoring network in late 2012 and hence the long-term and large-scale PM2.5 data were lacking before 2013. In this work, we developed a national-scale spatiotemporal ...linear mixed effects model to estimate the long-term PM2.5 concentrations in China from 1957 to 1964 and from 1973 to 2014 using ground visibility monitoring data as the primary predictor. The overall model-fitting and cross-validation R 2 is 0.72 and 0.71, suggesting that the model is not overfitted. Validation beyond the model year (2014) indicated that the model could accurately estimate historical PM2.5 concentrations at the monthly (R 2 = 0.71) level. The historical PM2.5 estimates suggest that air pollution is not a new environmental issue that occurs in the recent decades but a problem existing in a longer time before 1980. The PM2.5 concentrations have reached 60–80 μg/m3 in the north part of North China Plain during 1950s–1960s and increased to generally higher than 90 μg/m3 during 1970s. The results also show that the entire China experienced an overall increasing trend (0.19 μg/m3/yr, P < 0.001) in PM2.5 concentrations from 1957 to 2014 with fluctuations among different periods. This paper demonstrated visibility data allow us to understand the spatiotemporal characteristics of PM2.5 pollution in China in a long-term.
Estimating ground-level PM2.5 from satellite-derived aerosol optical depth (AOD) using a spatial statistical model is a promising new method to evaluate the spatial and temporal characteristics of ...PM2.5 exposure in a large geographic region. However, studies outside North America have been limited due to the lack of ground PM2.5 measurements to calibrate the model. Taking advantage of the newly established national monitoring network, we developed a national-scale geographically weighted regression (GWR) model to estimate daily PM2.5 concentrations in China with fused satellite AOD as the primary predictor. The results showed that the meteorological and land use information can greatly improve model performance. The overall cross-validation (CV) R 2 is 0.64 and root mean squared prediction error (RMSE) is 32.98 μg/m3. The mean prediction error (MPE) of the predicted annual PM2.5 is 8.28 μg/m3. Our predicted annual PM2.5 concentrations indicated that over 96% of the Chinese population lives in areas that exceed the Chinese National Ambient Air Quality Standard (CNAAQS) Level 2 standard. Our results also confirmed satellite-derived AOD in conjunction with meteorological fields and land use information can be successfully applied to extend the ground PM2.5 monitoring network in China.
Summary Background MicroRNAs (miRNAs) can be used as prognostic biomarkers in many types of cancer. We aimed to identify miRNAs that were prognostic in patients with nasopharyngeal carcinoma. Methods ...We retrospectively analysed miRNA expression profiles in 312 paraffin-embedded specimens of nasopharyngeal carcinoma from Sun Yat-sen University Cancer Center (Guangzhou, China) and 18 specimens of non-cancer nasopharyngitis. Using an 873 probe microarray, we assessed associations between miRNA signatures and clinical outcome in a randomly selected 156 samples (training set) and validated findings in the remaining 156 samples (internal validation set). We confirmed the miRNAs signature using quantitative RT-PCR analysis in 156 samples from a second randomisation of the 312 samples, and validated the miRNA signature in 153 samples from the West China Hospital of Sichuan University in Chengdu, China (independent set). We used the Kaplan-Meier method and log-rank tests to estimate correlations of the miRNA signature with disease-free survival (DFS), distant metastasis-free survival (DMFS), and overall survival. Findings 41 miRNAs were differentially expressed between nasopharyngeal carcinoma and non-cancer nasopharyngitis tissues. A signature of five miRNAs, each significantly associated with DFS, was identified in the training set. We calculated a risk score from the signature and classified patients as high risk or low risk. Compared with patients with low-risk scores, patients with high risk scores in the training set had shorter DFS (hazard ratio HR 2·73, 95% CI 1·46–5·11; p=0·0019), DMFS (3·48, 1·57–7·75; p=0·0020), and overall survival (2·48, 1·24–4·96; p=0·010). We noted equivalent findings in the internal validation set for DFS (2·47, 1·32–4·61; p=0·0052), DMFS (2·28, 1·09–4·80; p=0·030), and overall survival (2·87, 1·38–5·96; p=0·0051) and in the independent set for DFS (3·16, 1·65–6·04; p=0·0011), DMFS (2·39, 1·05–5·42; p=0·037), and overall survival (3·07, 1·34–7·01; p=0·0082). The five-miRNA signature was an independent prognostic factor. A combination of this signature and TNM stage had better prognostic value than did TNM stage alone in the training set (area under receiver operating characteristics 0·68 95% CI 0·60–0·76 vs 0·60 0·52–0·67; p=0·013), the internal validation set (0·70 0·61–0·78 vs 0·61 0·54–0·68; p=0·012), and the independent set (0·70 0·62–0·78 vs 0·63 0·56–0·69; p=0·032). Interpretation Identification of patients with the five-miRNA signature might add prognostic value to the TNM staging system and inform treatment decisions for patients at high risk of progression. Funding Science Foundation of Chinese Ministry of Health, National Natural Science Foundation of China, Pearl River Scholar Funded Scheme, Guangdong Key Scientific and Technological Innovation Program, Guangdong Natural Science Foundation, Fundamental Research Funds for the Central Universities.
The slow diffusion of cosmic rays could be common around pulsars as indicated by the recent observations of HAWC, which can significantly change the pulsar interpretation of the well-known positron ...excess. Meanwhile, the latest measurement by AMS-02 shows a clear high-energy cutoff in the positron spectrum. Here, we check all the identified pulsars under the two-zone diffusion model to explain the new AMS-02 data. We find that the candidates must be nearby and middle-aged. Geminga, which was generally believed to be a very likely candidate, has recently been disfavored by Fermi-LAT observations of the GeV γ-ray flux. Following recent studies which indicate that PSR B1055−52 is much closer to the Earth than previously assumed, we propose for the first time that PSR B1055−52 is the most promising source of the positron excess. PSR B1055−52 can well reproduce both the intensity and the high-energy cutoff of the AMS-02 positron spectrum.
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