粤港澳大湾区的贸易竞合关系及其优化路径     

宋周莺  祝巧玲  徐婧雅 《地理研究》2020,39(9):2065-2080

贸易合作是推动区域经济合作和区域一体化的关键环节。为了推动粤港澳大湾区建设,亟需明确粤港澳三地的贸易竞合关系,推动三地贸易协同发展,以期促进区域一体化、提升其在全球贸易格局中的地位。本文基于粤港澳大湾区在全球贸易格局中的地位及粤港澳三地的贸易关系分析,发现：① 粤港澳贸易规模整体呈上升态势,但湾区整体的金融环境仍需提升。② 随着广东与全球贸易联系不断增强,广东在贸易上逐步赶超香港,并与香港以转口贸易为主导的贸易模式在空间、商品结构方面存在较强竞争;港澳在转口贸易方面存在一定的潜在竞争。③ 广东在集聚水平上具有贸易竞争优势,香港在投资开放水平上具有显著优势,澳门在各项指标上均不存在明显优势。④ 粤港澳三地贸易联系不断加强,广东与港澳的贸易合作仍保留了部分“前店后厂”的特征,但加工贸易的比重正不断下降。⑤ 促进大湾区内部贸易合作,需发挥三地贸易优势,促进商品贸易错位发展,扩展各自贸易空间,加强服务贸易合作。  相似文献   

Smoothing of digital elevation models and the alteration of overland flow path length distributions     

Nigel Van Nieuwenhuizen  John B. Lindsay  Ben DeVries 《水文研究》2021,35(7):e14271

DEM smoothing is a common pre-processing technique used to remove undesirable roughness from a DEM. However, it is hypothesized that smoothing straightens and reduces the length of overland flow paths, which is an important factor controlling modelled time-to-peak flow. Currently, there is a lack of research comparing how different smoothing techniques alter the distribution of overland flow path length. Four low-pass filtering techniques were applied to three fine-resolution LiDAR DEMs of varying relief: the mean filter, the median filter, the Gaussian filter, and the feature-preserving DEM smoothing (FPDEMS) filter, each with different degrees of smoothing. Downslope-distance-to-stream distributions were then derived using D8 and D∞ flow directions and statistically compared to distributions derived from the unsmoothed DEM for each study site. The results indicate that the alteration of flow path length distributions as a result of smoothing is complex. Mean flow path lengths may decrease or increase in response to smoothing, depending on landscape relief and the derivation of flow directions, and generalized flow paths may become longer. The largest increase in mean flow path lengths was 19.2 m using the 21 × 21 median filter and D8 flow directions in the high-relief study site, relative to an unsmoothed mean length of 138.6 m in this site. The largest decrease in mean flow path length was 48.9 m using the 21 × 21 mean filter and D∞ flow directions in the low-relief study site, relative to an unsmoothed mean length of 290.9 m in this site. Furthermore, minimal flow path length alterations were achieved with the Gaussian filter when gentle smoothing is required, and with the FPDEMS filter when moderate to aggressive smoothing is required. These results suggest that an appropriate smoothing method should be chosen based on the relief of the landscape and the degree of smoothing required.  相似文献   

An (in‐)coherent metamorphic evolution of high‐P eclogites and their host rocks in the Chinese southwest Tianshan?          下载免费PDF全文

M. Meyer  R. Klemd  T. John  J. Gao  M. Menneken 《Journal of Metamorphic Geology》2016,34(2):121-146

In the (ultra‐)high‐P–low‐T metamorphic terrane of the Chinese South Tianshan, discontinuous mafic blocks and boudins (former upper oceanic crust) are now embedded in voluminous (mainly metasedimentary) host rocks. Two different models were proposed and relate the occurrence of both high‐P and ultra‐high‐P mafic and metasedimentary rocks to either (i) a tectonic mélange style exhumation, with no exhumation of coherent units, but different lithologies derived from different depths juxtaposed and intermingled during exhumation in the subduction channel, or (ii) the evolution of two coherent metamorphic belts: one with high‐P and the other with ultra‐high‐P conditions. In contrast to most previous studies in the Chinese South Tianshan which focused either on single eclogites or metasedimentary rocks (assumed as representative), this study concentrates on the systematic investigation of both mafic boudins and their immediate sedimentary host rocks, because the investigation of both lithologies and the comparison of their metamorphic evolution is crucial to reconstruct the geodynamical context of the whole (ultra‐)high‐P–low‐T metamorphic complex. Several sample pairs consisting of both lithologies were geochemically investigated and their respective metamorphic evolution was reconstructed using geothermobarometry and thermodynamic modelling. The latter approach considers changes in the mineral assemblage during the metamorphic evolution, as well as changes in mineral composition, which may help to determine the metamorphic history of a rock despite the preservation of critical mineral assemblages. All samples experienced a clockwise P–T path with overall maximum P–T conditions of 540–550 °C and 1.9–2.25 GPa for the host rocks, and 555–575 °C and 2.2–2.5 GPa for the eclogites. Peak‐metamorphic temperatures of ~525–540 °C of the metasedimentary host rocks were also confirmed by Raman spectroscopy of carbonaceous material. Results from thermobarometry and thermodynamic modelling are consistent with the observation that none of the samples contains mineral relicts indicating UHP conditions (like coesite in garnet) and neither conventional thermobarometry, nor thermodynamical modelling resulted in P–T conditions in the stability field of coesite. Thus, no evidence of ultra‐high‐P conditions was found. Given that the whole sampled river valley lies within the proposed ‘ultra‐high‐P sub‐belt’ and considering former studies, which showed that at other places within this ‘unit’ both ultra‐high‐P and high‐P rocks are now juxtaposed on a small scale, the formation of the whole (ultra‐)high‐P–low‐T metamorphic belt in the Chinese South Tianshan as a tectonic mélange style exhumation is more convincing than the formation and juxtaposition of two coherent metamorphic units with high‐P and ultra‐high‐P conditions respectively.  相似文献   

DEM study on the effect of particle breakage on the macro- and micro-behavior of rockfill sheared along different stress paths     

《Computers and Geotechnics》2017

The behavior of crushable rockfill sheared along different stress paths is studied using the discrete element method. Rockfill particles are modeled as breakable agglomerates, and reasonable consistency is found between the predicted and experimental results. The simulation highlights the influence of agglomerate breakage on both the macro- and micro-behavior of the assembly. The evolution of both the number and mode of agglomerate breakage during shearing is significantly influenced by the confining pressure, deviator stress ratio, and loading direction. The relationship between the deviator stress ratio on the macro-scale and the deviator fabric on the micro-scale along different stress paths is explored.  相似文献   

Metamorphic patterns and SHRIMP zircon ages of medium‐to‐high grade rocks from the Tongbai orogen,central China: implications for multiple accretion/collision processes prior to terminal continental collision     

X. C. LIU  B.‐M. JAHN  J. HU  S. Z. LI  X. LIU  B. SONG 《Journal of Metamorphic Geology》2011,29(9):979-1002

The Qinling‐Tongbai‐Dabie‐Sulu orogenic belt comprises a Palaeozoic accretion‐dominated system in the north and a Mesozoic collision‐dominated system in the south. A combined petrological and geochronological study of the medium‐to‐high grade metamorphic rocks from the diverse Palaeozoic tectonic units in the Tongbai orogen was undertaken to help elucidate the origins of Triassic ultrahigh‐pressure metamorphism and collision dynamics between the Sino‐Korean and Yangtze cratons. Peak metamorphic conditions are 570–610 °C and 9.3–11.2 kbar for the lower unit of the Kuanping Group, 630–650 °C and 6.6–8.9 kbar for the upper unit of the Kuanping Group, 550–600 °C and 6.3–7.7 kbar for the Erlangping Group, 770–830 °C and 6.9–8.5 kbar for the Qinling Group and 660–720 °C and 9.1–11.5 kbar for the Guishan complex. Reaction textures and garnet compositions indicate clockwise P–T paths for the amphibolite facies rocks of the Kuanping Group and Guishan complex, and an anticlockwise P–T path for the granulite facies rocks of the Qinling Group. Sensitive high‐resolution ion microprobe U–Pb zircon dating on metamorphic rocks and deformed granite/pegmatites revealed two major Palaeozoic tectonometamorphic events. (i) During the Silurian‐Devonian (c. 440–400 Ma), the Qinling continental arc and Erlangping intra‐oceanic arc collided with the Sino‐Korean craton. The emplacement of the Huanggang diorite complex resulted in an inverted thermal gradient in the underlying Kuanping Group and subsequent thermal relaxation during the exhumation. Meanwhile, the oceanic subduction beneath the Qinling continental arc produced magmatic underplating and intrusion, leading to granulite facies metamorphism followed by a near‐isobaric cooling path. (ii) During the Carboniferous (c. 340–310 Ma), the northward subduction of the Palaeo‐Tethyan ocean generated a medium P/T Guishan complex in the hangingwall and a high P/T Xiongdian eclogite belt in the footwall. The Guishan complex and Xiongdian eclogite belt are therefore considered to be paired metamorphic belts. Subsequent separation of the paired belts is inferred to be related to the juxtaposition of the Carboniferous eclogites with the Triassic HP metamorphic complex during continental subduction and exhumation.  相似文献   

MapInfo中道路拓扑与最优路径的实现     

任东风  徐爱功 《测绘工程》2011,20(6):53-56

文中以阜新市为例较为详细地讨论在公交线路网络中的拓扑结构建模,及基于公交线路网的弧段与节点间地理相关性的拓扑特征;并以MapInfo为平台,运用MapBasic语言,采用经典的Dijkstra最短路径算法,实现对阜新公交站点查询、公交线路查询、两站点间的最优路径查询功能.  相似文献   

基于多目标决策与层次分析法的最佳路径模型   总被引：1，自引：0，他引：1  

高露雄  王汇 《测绘与空间地理信息》2011,34(5):221-224

在最佳路径选择问题中,如何综合考虑多种因素的综合影响以及确定各因素的影响大小是一个关键性问题。通过建立最佳路径的道路层次模型,给出多目标决策模型和因素评分模型,并用层次分析法确定各影响因素权值的方法建立了基于多影响因素与综合评判的最佳路径模型。同时,在Dijkstra最短路径算法的基础上,应用文章所提模型方法实现了在多...  相似文献   

An Evidence of Aerosol Indirect Effect on Stratus Clouds from the Integrated Ground-Based Measurements at the ARM Shouxian Site          下载免费PDF全文

TANG Jin-Ping  WANG Pu-Cai  DUAN Min-Zheng  CHEN Hong-Bin  XIA Xiang-Ao  LIAO Hong 《大气和海洋科学快报》2011,4(2):65-69

The aerosol effect on clouds was explored using remote sensing of aerosol and cloud data at Shouxian, China. Non-precipitation, ice-free, and overcast clouds were firstly chosen by a combination of sky images from the Total Sky Imager (TSI), cloud base heights from the Ceilometer, and vertical temperature profiles from the Balloon-Borne Sounding System (BBSS). Six cases were chosen in summer, and seven in autumn. The averaged cloud effective radii (re), cloud optical depth (COD), aerosol total light scattering coefficient (σ), and liquid water path (LWP) are, respectivey, 6.47 μm, 35.4, 595.9 mm-1, 0.19 mm in summer, and 6.07 μm, 96.0, 471.7 mm-1, 0.37 mm in autumn. The correlation coefficient between re and σ was found to change from negative to positive value as LWP increases.  相似文献   

Autopilot control synthesis for path tracking maneuvers of underwater vehicles     

Sam-Sang YOU  Hyeung-Sik CHOI  Hwan-Seong KIM  Han-Il PARK 《中国海洋工程》2011,25(2):237-249

This paper is concerned with the robust control synthesis of autonomous underwater vehicle(AUV) for general path following maneuvers.First,we present maneuvering kinematics and vehicle dynamics in a unified framework.Based on H∞ loop-shaping procedure,the 2-DOF autopilot controller has been presented to enhance stability and path tracking.By use of model reduction,the high-order control system is reduced to one with reasonable order,and further the scaled low-order controller has been analyzed in both the frequency and the time domains.Finally,it is shown that the autopilot control system provides robust performance and stability against prescribed levels of uncertainty.  相似文献   

内蒙古西部额济纳旗及邻区二叠系烃源岩热演化与油气的关系     

韩伟  姜亭  李玉宏  魏建设 《地质通报》2011,30(6):911-915

分析了额济纳旗及其邻区二叠系烃源岩热演化史与油气生成的关系。根据镜质组反射率、包裹体均一温度、磷灰石裂变径迹等资料得出研究区达到最大埋深时的古地温梯度,分析额济纳旗地区热演化史的信息,进一步研究了热演化与油气生成的关系。研究结果表明,额济纳旗地区在白垩纪达到最大埋深,古地温梯度为4.1～5.5℃/100m。通过与邻区查干凹陷比较分析,认为额济纳旗地区古地温梯度高于现今的地温梯度,二叠系烃源岩热演化程度主要受古地温场的控制。热演化史与油气关系的研究结果表明,额济纳旗部分地区二叠系烃源岩在晚二叠世已进入油气生成期,生烃阶段以干气为主,在早白垩世热演化程度达到最高。  相似文献