绿色空间对休闲性体力活动影响的社区分异 ——以广州市为例     

戴颖宜  朱战强  周素红 《热带地理》2019,39(2):237-246

以广州市20个典型社区为例，构建多元线性回归模型，探讨了绿色空间对居民休闲性体力活动的影响，并剖析绿色空间对不同类型社区居民休闲性体力活动影响的作用机制。结果发现：1）不同类型社区居民的休闲性体力活动水平存在明显差异，低档社区的为782.99 MET-min/w，中档社区的为871.70 MET-min/w，高档社区的为1 227.91 MET-min/w；2）影响不同类型社区居民休闲性体力活动水平的绿色空间因素有所不同，低档社区、中档社区和高档社区的显著因子分别为“到最近公园广场距离”“邻里绿化覆盖率”和“健身活动设施数量”；3）绿色空间对休闲性体力活动水平影响的作用机制存在社区差异，低档社区居民休闲性体力活动主要受到成本作用的约束，中档社区居民主要受绿化环境作用影响，而高档社区居民主要受机会作用影响。  相似文献   

地中海直布罗陀海峡附近内孤立波的地球物理特征          下载免费PDF全文

孙绍箐  张锟  宋海斌 《地球物理学报》2019,62(7):2622-2632

本文主要利用地震海洋学方法研究地中海直布罗陀海峡附近内孤立波的结构特征，此处内孤立波为第一模态下沉型，为中幅度和大幅度内孤立波，垂向振幅最大可达74.5 m，振幅随深度增加呈增大趋势，传播速度随振幅增大而增大，可以确定"真"最大振幅位置位于密跃层附近.由于类多普勒效应和孤立波与测量船之间存在夹角的原因，从地震剖面上得到的为视半高宽参数，需要进行校正后才能得到比较真实的半高宽参数，校正后半高宽最高可达到1721.8 m，但是校正后的半高宽与理论结果有些差距，这可能与内孤立波的发育稳定程度有关.随着内孤立波包不断向东运动，整体波宽变大，垂向速度变小.本文将地震海洋学方法拓展应用于地中海区域内孤立波分析，进一步证明了利用地震海洋学方法研究海水运动的可行性.  相似文献   

Sediment flux-driven channel geometry adjustment of bedrock and mixed gravel–bedrock rivers     

Edwin R.C. Baynes  Dimitri Lague  Philippe Steer  Stéphane Bonnet  Luc Illien 《地球表面变化过程与地形》2020,45(14):3714-3731

Sediment supply (Q_s) is often overlooked in modelling studies of landscape evolution, despite sediment playing a key role in the physical processes that drive erosion and sedimentation in river channels. Here, we show the direct impact of the supply of coarse-grained, hard sediment on the geometry of bedrock channels from the Rangitikei River, New Zealand. Channels receiving a coarse bedload sediment supply are systematically (up to an order of magnitude) wider than channels with no bedload sediment input for a given discharge. We also present physical model experiments of a bedrock river channel with a fixed water discharge (1.5 l min⁻¹) under different Q_s (between 0 and 20 g l⁻¹) that allow the quantification of the role of sediment in setting the width and slope of channels and the distribution of shear stress within channels. The addition of bedload sediment increases the width, slope and width-to-depth ratio of the channels, and increasing sediment loads promote emerging complexity in channel morphology and shear stress distributions. Channels with low Q_s are characterized by simple in-channel morphologies with a uniform distribution of shear stress within the channel while channels with high Q_s are characterized by dynamic channels with multiple active threads and a non-uniform distribution of shear stress. We compare bedrock channel geometries from the Rangitikei and the experiments to alluvial channels and demonstrate that the behaviour is similar, with a transition from single-thread and uniform channels to multiple threads occurring when bedload sediment is present. In the experimental bedrock channels, this threshold Q_s is when the input sediment supply exceeds the transport capacity of the channel. Caution is required when using the channel geometry to reconstruct past environmental conditions or to invert for tectonic uplift rates, because multiple configurations of channel geometry can exist for a given discharge, solely due to input Q_s. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

Downvalley fining of hillslope sediment in an alpine catchment: implications for downstream fining of sediment flux in mountain rivers     

Leonard S. Sklar  Clifford S. Riebe  Jennifer Genetti  Shirin Leclere  Claire E. Lukens 《地球表面变化过程与地形》2020,45(8):1828-1845

The size distributions of sediment delivered from hillslopes to rivers profoundly influence river morphodynamics, including river incision into bedrock and the quality of aquatic habitat. Yet little is known about the factors that influence size distributions of sediment produced by weathering on hillslopes. We present results of a field study of hillslope sediment size distributions at Inyo Creek, a steep catchment in granitic bedrock of the Sierra Nevada, USA. Particles sampled near the base of hillslopes, adjacent to the trunk stream, show a pronounced decrease in sediment size with decreasing sample elevation across all but the coarsest size classes. Measured size distributions become increasingly bimodal with decreasing elevation, exhibiting a coarse, bouldery mode that does not change with elevation and a more abundant finer mode that shifts from cobbles at the highest elevations to gravel at mid elevations and finally to sand at low elevations. We interpret these altitudinal variations in hillslope sediment size to reflect changes in physical, chemical, and biological weathering that can be explained by the catchment's strong altitudinal gradients in topography, climate, and vegetation cover. Because elevation and travel distance to the outlet are closely coupled, the altitudinal trends in sediment size produce a systematic decrease in sediment size along hillslopes parallel to the trunk stream. We refer to this phenomenon as ‘downvalley fining.’ Forward modeling shows that downvalley fining of hillslope sediment is necessary for downstream fining of the long-term average flux of coarse sediment in mountain landscapes where hillslopes and channels are coupled and long-term net sediment deposition is negligible. The model also shows that abrasion plays a secondary role in downstream fining of coarse sediment flux but plays a dominant role in partitioning between the bedload and suspended load. Patterns observed at Inyo Creek may be widespread in mountain ranges around the world. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Channel stability in steep gravel–cobble streams is controlled by the coarse tail of the bed material distribution     

Brett C. Eaton  Lucy G. MacKenzie  William H. Booker 《地球表面变化过程与地形》2020,45(14):3639-3652

Researchers have associated channel-forming flows with reach-average shear stresses close to the entrainment threshold for the surface D₅₀ . We conducted experiments using a model of a generic steep, gravel–cobble stream to test this association. Our results suggest that channel-forming flows fully mobilize the D₅₀ , and produce shear stresses close to the entrainment threshold for the largest grains in the bed. The channel dimensions were set by flows capable of mobilizing between 85% and 90% of the bed surface, which produced a brief period of lateral instability lasting about 1 h, followed by a prolonged period of relative stability during which modest adjustments occurred, but during which the reach-average hydraulics remained about the same. The adjustments during the unstable phase of the experiments are characterized by rapid bank erosion, extensive deposits on the channel bed and a restructuring of the major morphologic elements of the stream. The adjustments during the stable phase of the experiments involved barform migration and bed surface coarsening but did not appreciably modify the physical template established by the end of the unstable phase. The behaviour we observed is not consistent with the concept of a dynamic equilibrium associated with a formative flow that is just capable of entraining the bed surface D₅₀ . Instead, it suggests that rapid adjustments occur once a stability threshold is exceeded, which creates a template that constrains channel activity until another event drives the system across the stability threshold, and re-sets the template. While we believe that it is probably too simplistic to associate a channel-forming discharge with the entrainment threshold for a single grain size, our results suggest that the D₉₅ is a more logical choice than the D₅₀ © 2020 John Wiley & Sons, Ltd.  相似文献   

Controls on the lateral channel-migration rate of braided channel systems in coarse non-cohesive sediment     

Aaron Bufe  Jens M. Turowski  Douglas W. Burbank  Chris Paola  Andrew D. Wickert  Stefanie Tofelde 《地球表面变化过程与地形》2019,44(14):2823-2836

Lateral movements of alluvial river channels control the extent and reworking rates of alluvial fans, floodplains, deltas, and alluvial sections of bedrock rivers. These lateral movements can occur by gradual channel migration or by sudden changes in channel position (avulsions). Whereas models exist for rates of river avulsion, we lack a detailed understanding of the rates of lateral channel migration on the scale of a channel belt. In a two-step process, we develop here an expression for the lateral migration rate of braided channel systems in coarse, non-cohesive sediment. On the basis of photographic and topographic data from laboratory experiments of braided channels performed under constant external boundary conditions, we first explore the impact of autogenic variations of the channel-system geometry (i.e. channel-bank heights, water depths, channel-system width, and channel slope) on channel-migration rates. In agreement with theoretical expectations, we find that, under such constant boundary conditions, the laterally reworked volume of sediment is constant and lateral channel-migration rates scale inversely with the channel-bank height. Furthermore, when channel-bank heights are accounted for, lateral migration rates are independent of the remaining channel geometry parameters. These constraints allow us, in a second step, to derive two alternative expressions for lateral channel-migration rates under different boundary conditions using dimensional analysis. Fits of a compilation of laboratory experiments to these expressions suggest that, for a given channel bank-height, migration rates are strongly sensitive to water discharges and more weakly sensitive to sediment discharges. In addition, external perturbations, such as changes in sediment and water discharges or base level fall, can indirectly affect lateral channel-migration rates by modulating channel-bank heights. © 2019 The Author. Earth Surface Processes and Landforms published by John Wiley & Sons, Ltd. © 2019 The Author. Earth Surface Processes and Landforms published by John Wiley & Sons, Ltd.  相似文献   

Research and Test of Real-time Search Algorithm of Fast Radio Bursts Based on GPU Acceleration     

WANG Jun  CHEN Mao-zheng  PEI Xin  WANG Zhi-qiao 《Chinese Astronomy and Astrophysics》2018,42(2):313-324

In order to satisfy the research need of Nanshan 25 m radio telescope of Xinjiang Astronomical Observatory (XAO) and study the key technology of the planned QiTai radio Telescope (QTT), on the basis of the original CPU (Central Processing Unit)-based real-time search algorithm of FRBs (Fast Radio Bursts), we have studied the GPU (Graphics Processing Unit)-based real-time search algorithm of FRBs, and built the corresponding real-time search system of FRBs. We have made the comparison and analysis on the GPU system and CPU system, the test result shows that under a given searching accuracy, the speed of the GPU-accelerated algorithm is improved by 35–45 times compared with that of the CPU algorithm.  相似文献   

城市居民日常身体活动时空分异特征及影响因素   总被引：2，自引：2，他引：0  

姜玉培  甄峰  赵梦妮  曹晨 《地理科学》2019,39(9):1496-1506

依托南京主城区居民日常身体活动调查数据,基于身体活动时空维度,挖掘城市居民日常身体活动时空分异特征,并采用混合效应模型探究身体活动分异的影响因素。研究表明：① 居民日常身体活动时空异质特征明显。工作日/非工作日不同类型身体活动时间安排及个体间差异均显著;工作性、交通性、家务性身体活动空间制约明显,而休闲性身体活动空间分布更具弹性;与工作日相比,非工作日不同类型身体活动空间范围变化收敛与扩散特征并存。② 活动空间范围、个人社会经济属性、自身健康状况对居民日常身体活动分异均具有显著影响。具体而言,居民日常活动空间范围决定身体活动的空间适应与选择;社会分工差异导致不同性别、年龄人群身体活动具有指向性;身体活动时间出现与个人社会经济实力倒置现象;而良好健康状态会激励居民日常身体活动的保持。  相似文献   

Evaluation of clayed silt properties on the behavior of hydrate production in South China Sea     

《China Geology》2020,3(3):362-368

Gas hydrate is one kind of potential energy resources that is buried under deep seafloor or frozen areas. The first trial offshore production from the silty reservoir was conducted in the South China Sea by the China Geological Survey (CGS). During this test, there were many unique characteristics different from the sand reservoir, which was believed to be related to the clayed silt physical properties. In this paper, simulation experiments, facilities analysis, and theoretical calculation were used to confirm the hydrate structure, reservoir thermo-physical property, and bond water movement rule. And the behavior of how they affected production efficiency was analyzed. The results showed that: It was reasonable to use the structure I rather than structure II methane hydrate phase equilibrium data to make the production plan; the dissociation heat absorbed by hydrate was large enough to cause hydrate self-protection or reformation depend on the reservoir thermal transfer and gas supply; clayed silt got better thermal conductivity compared to coarse grain, but poor thermal convection especially with hydrate; clayed silt sediment was easy to bond water, but the irreducible water can be exchanged to free water under high production pressure, and the most obvious pressure range of water increment was 1.9–4.9 MPa.  相似文献   

基于高分遥感影像的建筑物侧面信息提取及其高度计算     

宋旭东  曹文峰  冯德俊  张星星 《北京测绘》2020,(3):296-300

本文选取成都市某一区域建筑物A、B为研究对象,采用分辨率为0.61 m的Quick bird影像,运用图像分割法和LVQ神经网络算法,提取建筑物侧面信息,根据假设法原理,构建高度计算物理模型,求取建筑物高度。对比实测数据,结合可能影响实验结果的实地因素、遥感影像因素进行精度分析与评价,探讨基于高分遥感影像的建筑物侧面信息提取和高度计算的方法。结果表明,LVQ神经网络算法在建筑物侧面提取和高度计算中有更好的应用价值,精度高达94%。  相似文献