We collected high-quality teleseismic events recorded by 12 broadband seismographs deployed in the Anyuan Coal Mine and its adjacent areas in Pingxiang City, Jiangxi Province nearly two years. The H-κ-c stacking method was employed to obtain the crustal thickness, Poisson's ratio distribution, and then the crustal structure characteristics below the stations are obtained by using the time-domain linear inversion method. The crustal thickness in the Anyuan Coal Mine and its adjacent areas ranges from approximately 32 ∼ 35 km, with an average thickness of 33 km, which is consistent with the crustal thickness results in South China obtained by previous studies using receiver function method. The average Poisson's ratio of the internal medium in the study area varies between 0.22 and 0.25, which is lower than the global average of 0.27, indicating that the crustal composition is mainly composed of intermediate-acidic or felsic rocks. There is a weak negative correlation between Poisson's ratio and crustal thickness results in the Anyuan Coal Mine and its adjacent areas, suggesting that the absence of mafic-ultramafic materials in the lower crust is related with crustal delamination. The crust-mantle structure beneath the seismic stations mainly consists of three velocity discontinuity interfaces, with the first interface at a depth of approximately 1.5 km, the second one about 10∼ 15 km, and the third discontinuity being the Moho. The study also indicates that the results obtained by the H-κ-c stacking method are significantly better than those obtained by H-κ method, effectively reducing the standard deviation and dispersion of crustal thickness and VP/VS ratio.
An oil and gas reservoir is a typical porous medium. The frequency-dependent amplitude variation with offset (FDAVO) is a recently developed technology for reservoir prediction. Traditional FDAVO is normally based on the Zoeppritz equation and does not involve the parameter of wave attenuation. The effect of attenuation on FDAVO was discussed based on the porous media theory. The wave reflections on the top interface of the reservoir and on the interface between oil-saturated and water-saturated reservoirs are simulated and analyzed. The results indicate that: the effects of attenuation on the reflection of slow compression waves are obvious for both interfaces; the effects of attenuation on the reflection of fast compression waves are slight for the top interface of the reservoir and more obvious for the interface between the oil-saturated and water-saturated reservoirs, especially in the lower frequency range; the effects of attenuation on the reflection of conversed shear wave are slight for the top interface of the reservoir and complicated for the interface between the oil-saturated and water-saturated reservoirs, especially in the frequency range of 0–50.
In this study, we classified the variability in snow cover persistence across China by using a novel method; continuous snow cover days and variability of snow cover were used as the evaluation indicators based on a long-term Advanced Very High Resolution Radiometer (AVHRR) snow cover extent (SCE) product. The product has been generated by the snow research team in the Northwest Institute of Eco-Environment and Resources (NIEER), Chinese Academy of Sciences. There were obvious differences in snow cover classification in three snow cover areas (northern Xinjiang, northeast China, and the Tibetan Plateau): northern Xinjiang was dominated by persistent snow cover, most regions of northeast China were covered by persistent and periodic variable snow cover. There was the most abundant snow cover classification in the Tibetan Plateau. The extents of persistent and periodic variable snow cover were gradually shrinking due to rising temperatures and decreasing snowfall during 1981–2019. In contrast, non-periodic variable snow cover areas increased significantly. This method takes into account the stability, continuity, and variability of snow cover, and better captures the characteristics and changes of snow cover across China. Based on our research, we found that snow disasters in ephemeral-type (belong to non-periodic variable snow cover) regions cannot be well prevented because of the unfixed snow cover timing. Therefore, we recommend that monitoring and forecasting of snow cover in these snow cover regions should be strengthened.
Compared with other morphological nanomaterials, nanorods have many unique properties that are closely related to their thermal stability. However, current studies on melting thermodynamic theory of nanorods are still not perfect, and the mechanism and the quantitative regularities of the effect of size of nanorods on melting thermodynamics still remain unclear. Herein, we proposed a melting model of nanorods, derived the thermodynamic relations (free of any adjustable parameters) between the melting temperature, melting enthalpy, and melting entropy, respectively, and the radius of nanorods, and discussed the mechanism of the effect of nanorods and the size dependences of melting thermodynamic properties. Experimentally, taking the melting of Se nanorods as an experimental system, Se nanorods with different diameters were prepared by a Na2SeSO3 disproportionation method, and then the melting temperature and melting thermodynamic properties were determined by differential scanning calorimetry. The effects of the diameter of Se nanorods on the melting temperature and the melting thermodynamic properties were obtained. The experimental results are consistent with the theoretical relations. Both theoretical and experimental results demonstrate that the radius and length of nanorods have significant effects on the melting temperature and the melting thermodynamic properties; for nanorods with a large aspect ratio, the main factors of influence are interfacial tension and radius. Compared with spherical nanoparticles with the same radius, the reduced values of the melting temperature and the thermodynamic properties of nanorods are just half of those corresponding to spherical nanoparticles; the melting temperature, the melting enthalpy, and the melting entropy decrease with the decrease in the radius, and when the radius exceeds 10 nm, these physical quantities are all linearly related to the reciprocal of the radius. The theory can describe the quantitative size-dependent melting thermodynamic properties of nanorods, explain and predict the melting behaviors of nanorods.
Eikonal solvers in the Cartesian coordinates often suffer from source singularity due to the plane-wave assumption for the wavefront near the source point. Traveltime errors induced by the source singularity near the source point will spread to the whole domain and reduce the accuracy of subsequent traveltimes. The source singularity can be avoided if the eikonal equation is formulated and solved in the polar/spherical coordinates. However, the grid in the polar/spherical coordinates will cause sparse non-uniform resampling in the region far away from the source point after the traveltime is transformed back to the Cartesian mesh, hence reducing the uniform accuracy in this region. To deal with the source singularity and maintain uniform accuracy, we introduce a hybrid fast sweeping method that computes the traveltime near the source in the polar/spherical coordinates and computes the traveltime far away from the source in the Cartesian coordinates. The source singularity near the source point is resolved in the polar/spherical coordinates, and the uniform accuracy is achieved by switching to the Cartesian coordinates away from the source point. Numerical examples are presented to demonstrate the method.
Abstract The group of avian sarcoma and leukosis virus (ASLV) in chickens contains six highly related subgroups, A to E and J. Four genetic loci, tva , tvb , tvc and tvj , encode for corresponding receptors that determine the susceptibility to the ASLV subgroups. The prevalence of ASLV in hosts may have imposed strong selection pressure toward resistance to ASLV infection and the resistant alleles in all four receptor genes have been identified. In this study, two new alleles of the tva receptor gene, tva r5 and tva r6 , with similar intronic deletions were identified in Chinese commercial broilers. These natural mutations delete the deduced branch point signal within the first intron, disrupting mRNA splicing of the tva receptor gene and leading to the retention of intron 1 and introduction of premature TGA stop codons in both the longer and shorter tva isoforms. As a result, decreased susceptibility to subgroup A ASLV in vitro and in vivo was observed in the subsequent analysis. In addition, we identified two groups of heterozygous allele pairs which exhibited quantitative differences in host susceptibility to ASLV-A. This study demonstrated that defective splicing of the tva receptor gene can confer genetic resistance to ASLV subgroup A in the host.
Manganese nodule coverage is estimated based on multi-beam and deep-towed video nodule survey profiles of about 1,700 km in the China Pioneer Area of Eastern Pacific. Two statistical equations for estimating nodule coverage are derived separately from the multi-beam normal incidence amplitude data and angular amplitude data based on theoretical analysis of influence factors on multi-beam amplitude data. Predictions generated by the normal incidence amplitude model fall within 5% of real nodule coverage, and theoretically calculated angular amplitude data fits well with the original multi-beam amplitudes at incident angles larger than 20° according to nodule coverage estimated from the deep-towed video data.
Snow is one of the most important components of the cryosphere. Remote sensing of snow focuses on the retrieval of snow parameters and monitoring of variations in snow using satellite data. These parameters are key inputs for hydrological and atmospheric models. Over the past 30 years, the field of snow remote sensing has grown dramatically in China. The 30-year achievements of research in different aspects of snow remote sensing in China, especially in (1) methods of retrieving snow cover, snow depth/snow water equivalent, and grain size and (2) applications to snowmelt runoff modeling, snow response on climate change, and remote sensing monitoring of snow-caused disasters are reviewed/summarized. The importance of the first remote sensing experiment on snow parameters at the upper reaches of the Heihe River Basin, in 2008, is also highlighted. A series of experiments, referred to as the Cooperative Observation Series for Snow (COSS), focus on some key topics on remote sensing of snow. COSS has been implemented for 3 years and will continue in different snow pattern regions of China. The snow assimilation system has been established in some regions using advanced ensemble Kalman filters. Finally, an outlook for the future of remote sensing of snow in China is given.
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