北京降尘成分及来源的探讨

北京市降尘在风沙天气中占有显著地位。本文依据降尘的最新资料-1988年4月的一次大风降尘重矿物分析资料与北京市各类沙土的地矿背景值比较, 差异很大, 推测为外来; 又重新分析了"无风降尘"的微量元素分析资料, 认为其主要组成为工业、交通的排放物。     

中国“蓝色粮仓”战略的研究热点与前沿探析

科学构建“蓝色粮仓”战略的理论体系对于保障中国粮食安全意义重大,通过对“蓝色粮仓”战略的研究热点与前沿进行总结分析,对后续深化其研究内容具有较强现实意义。基于中国学术期刊(CNKI)数据库,通过软件CiteSpace对1992—2020年“蓝色粮仓”战略相关文献进行统计分析。《中国渔业经济》《中国海洋大学学报(社会科学...     

Embodied carbon emissions in China-US trade

China-US trade holds great significance for the world's political and economic landscape. Since 2018, the US government has imposed additional tariffs on Chinese exports on the grounds of the US trade deficit with China. However, the transfer of pollutants embodied in trade and the differences in environmental costs between China and the US have not been widely recognized. In this study, we quantify the embodied carbon emissions(the "virtual" emissions associated with trade and consumption) in China-US trade by constructing a carbon dioxide emissions inventory and a multiregional input-output model.The study shows that the US benefits from a trade surplus of environmental costs by importing energy-intensive and pollutionintensive products from China, which increases China's environmental pollution and abatement costs. In 2017, 288 Mt CO_2 emissions were associated with products produced in China but finally consumed in the US, and only 46 Mt CO_2 were associated with the US products that were consumed in China. From this perspective, China-US trade results in a net transfer of 242 Mt CO_2 per year from the US to China, accounting for approximately 5% of the total CO_2 emissions in the US. More importantly, for Chinese products exported to the US, the carbon emissions embodied in one unit of economic value amount to 0.92 kg/$(RMB:USD=6.8:1), but for US products exported to China, the carbon emissions embodied in one unit of economic value amount to 0.53 kg/$, which means China will incur environmental costs that are 74% higher than those of the US while enjoying the same economic benefits. This environmental trade deficit has burdened China with higher environmental costs than economic benefits.To address this environmental trade deficit, China should actively promote further industrial upgrading and energy structure adjustment and increase investment in innovation and RD, thereby increasing the value added per unit of export products and reducing the environmental cost of producing export products.     

中国海洋交通运输业的绿色全要素生产率及其空间分异

为促进中国海洋交通运输业的可持续发展和区域均衡发展,文章基于相关面板数据,将非期望产出即碳排放量纳入评价指标体系,运用SBM-ML指数测算2006-2017年中国海洋交通运输业的绿色全要素生产率,进一步采用GINI系数、对数离差均值、泰尔指数和重心-标准差椭圆模型研究其空间分异。研究结果表明：中国海洋交通运输业的绿色全要素生产率保持增长态势,仍具有较大的效率改善空间;中国海洋交通运输业的绿色全要素生产率具有显著的空间非均衡性,其中中效率水平地区的区域差异更大,而高效率水平地区的区域差异变动更明显;中国海洋交通运输业的绿色全要素生产率的重心移动呈现“S-N-S”特征,具有“EN-WS”的空间格局但偏移趋势不明显。根据研究结果提出建议：重视区域协调合作,缩小生产效率差异;加快能源结构转型,提高技术创新能力;促进产业集聚发展,提升综合管理水平。     

Three-dimensional properties of mesoscale cyclonic warm-core and anticyclonic cold-core eddies in the South China Sea

In general, a mesoscale cyclonic (anticyclonic) eddy has a colder (warmer) core, and it is considered as a cold (warm) eddy. However, recently research found that there are a number of “abnormal” mesoscale cyclonic (anticyclonic) eddies associated with warm (cold) cores in the South China Sea (SCS). These “abnormal” eddies pose a challenge to previous works on eddy detection, characteristic analysis, eddy-induced heat and salt transports, and even on mesoscale eddy dynamics. Based on a 9-year (2000–2008) numerical modelling data, the cyclonic warm-core eddies (CWEs) and anticyclonic cold-core eddies (ACEs) in the SCS are analyzed. This study found that the highest incidence area of the “abnormal” eddies is the northwest of Luzon Strait. In terms of the eddy snapshot counting method, 8 620 CWEs and 9 879 ACEs are detected, accounting for 14.6% and 15.8% of the total eddy number, respectively. The size of the “abnormal” eddies is usually smaller than that of the “normal” eddies, with the radius only around 50 km. In the generation time aspect, they usually appear within the 0.1–0.3 interval in the normalized eddy lifespan. The survival time of CWEs (ACEs) occupies 16.3% (17.1%) of the total eddy lifespan. Based on two case studies, the intrusion of Kuroshio warm water is considered as a key mechanism for the generation of these “abnormal” eddies near the northeastern SCS.     

Reflection full-waveform inversion using a modified phase misfit function

Reflection full-waveform inversion (RFWI) updates the low- and highwavenumber components, and yields more accurate initial models compared with conventional full-waveform inversion (FWI). However, there is strong nonlinearity in conventional RFWI because of the lack of low-frequency data and the complexity of the amplitude. The separation of phase and amplitude information makes RFWI more linear. Traditional phase-calculation methods face severe phase wrapping. To solve this problem, we propose a modified phase-calculation method that uses the phase-envelope data to obtain the pseudo phase information. Then, we establish a pseudophase-information-based objective function for RFWI, with the corresponding source and gradient terms. Numerical tests verify that the proposed calculation method using the phase-envelope data guarantees the stability and accuracy of the phase information and the convergence of the objective function. The application on a portion of the Sigsbee2A model and comparison with inversion results of the improved RFWI and conventional FWI methods verify that the pseudophase-based RFWI produces a highly accurate and efficient velocity model. Moreover, the proposed method is robust to noise and high frequency.     

Acoustic viscoelastic modeling by frequency-domain boundary element method

Earth medium is not completely elastic, with its viscosity resulting in attenuation and dispersion of seismic waves. Most viscoelastic numerical simulations are based on the finite-difference and finite-element methods. Targeted at viscoelastic numerical modeling for multilayered media, the constant-Q acoustic wave equation is transformed into the corresponding wave integral representation with its Green’s function accounting for viscoelastic coefficients. An efficient alternative for full-waveform solution to the integral equation is proposed in this article by extending conventional frequency-domain boundary element methods to viscoelastic media. The viscoelastic boundary element method enjoys a distinct characteristic of the explicit use of boundary continuity conditions of displacement and traction, leading to a semi-analytical solution with sufficient accuracy for simulating the viscoelastic effect across irregular interfaces. Numerical experiments to study the viscoelastic absorption of different Q values demonstrate the accuracy and applicability of the method.     

Glacial bedforms in the Northwind Abyssal Plain,Chukchi Borderland

A series of sub-parallel linear glacial scours are identified on the crest of the Baoshi Seamount in the Northwind Abyssal Plain by compiling new multibeam data acquired during the 9th Chinese Arctic Research Expedition (CHINARE-Arc9) in 2018 and previously published data. The new data reveal scours that developed at water depths of 850–1 030 m with an orientation of about 75°/255°. The maximum water depth occurs in the southernmost scour and is deeper than that from previous investigations, which showed a maximum scouring depth of about 900 m on the seamount. The topographic and geomorphological characteristics suggest that these scours resulted from erosion by the ice shelf extending from the Chukchi margin and/or Laurentide Ice Sheet that grounded on the crest of the seamount and moved in a NE–SW direction. Other possibilities of their genesis include armadas of large icebergs/multi-keel icebergs calved from the Chukchi Shelf or the Laurentide Ice Sheet. The new data provide new constraints for assessing the extent and volume of the ice sheet in the Chukchi area during glacial maxima.     

Multi-beam and seismic investigations of the active Haima cold seeps,northwestern South China Sea

To confirm the seabed fluid flow at the Haima cold seeps, an integrated study of multi-beam and seismic data reveals the morphology and fate of four bubble plumes and investigates the detailed subsurface structure of the active seepage area. The shapes of bubble plumes are not constant and influenced by the northeastward bottom currents, but the water depth where these bubble plumes disappear (630–650 m below the sea level) (mbsl) is very close to the upper limit of the gas hydrate stability zone in the water column (620 m below the sea level), as calculated from the CTD data within the study area, supporting the “hydrate skin” hypothesis. Gas chimneys directly below the bottom simulating reflectors, found at most sites, are speculated as essential pathways for both thermogenic gas and biogenic gas migrating from deep formations to the gas hydrate stability zone. The fracture network on the top of the basement uplift may be heavily gas-charged, which accounts for the chimney with several kilometers in diameter (beneath Plumes B and C). The much smaller gas chimney (beneath Plume D) may stem from gas saturated localized strong permeability zone. High-resolution seismic profiles reveal pipe-like structures, characterized by stacked localized amplitude anomalies, just beneath all the plumes, which act as the fluid conduits conveying gas from the gas hydrate-bearing sediments to the seafloor, feeding the gas plumes. The differences between these pipe-like structures indicate the dynamic process of gas seepage, which may be controlled by the build-up and dissipation of pore pressure. The 3D seismic data show high saturated gas hydrates with high RMS amplitude tend to cluster on the periphery of the gas chimney. Understanding the fluid migration and hydrate accumulation pattern of the Haima cold seeps can aid in the further exploration and study on the dynamic gas hydrate system in the South China Sea.     

三维激光点云数据在既有地下人防工程BIM模型重建中的应用

BIM模型的创建是实现BIM技术应用的第一步,常见的基于CAD图纸的BIM模型创建方法存在建模效率低、空间表现不直观的缺点、本丈以某地下人防工程的B1M模型重建为例,结合=维激光扫描技术,详细阐述了基于维激光点云数据的BIM模型重建过程,主要步骤为:①利用FARO Focus3DX330获取海量点云数据;②利用FARO SCENE软件完成点云数据的配准拼接,滤波去噪.贴图输出;③按目标对象几何形状和功能特征的差异,利用Autodesk Revil分别完成线性类、构件连接类、单体目标类点云对象的B1M模型制作.研究表明,利用三维激光扫描技术可以很好地完成BIM模型的重建.而且具有建模精度高、现场还原度好的优势.