On the origin of the compact H ii regions around massive stellar clusters

The existence of compact H?ii regions around massive stellar clusters with ages exceeding several Myr challenges our understanding of the physical processes occurring inside such clusters, and their impact on the interstellar medium of the host galaxy. Here, we summarize our recent results dealing with the hydrodynamics of matter ejected by massive stars inside the cluster and show that compact H?ii regions found around some massive clusters may indicate that these are evolving in a bimodal hydrodynamic regime. The latter is characterized by the accumulation of the injected matter in the central, thermally unstable zone, and by the ejection of mass supplied by massive stars in the outer regions of the cluster.     

Model prediction capacity of ephemeral gully evolution in conservation tillage systems

Ephemeral gully (EG) erosion has an important impact on agricultural soil losses and increases field surface hydrology connectivity and transport of pollutants to nearby water bodies. Watershed models including an EG component are scarce and not yet properly evaluated. The objective of this study is to evaluate the capacity of one such tool, AnnAGNPS, to simulate the evolution of two EG formed in a conservation tillage system. The dataset for model testing included runoff measurements and EG morphological characteristics during 3 years. Model evaluation focused on EG evolution of volume, width, and length model outputs, and included calibration and testing phases and a global sensitivity analysis (GSA). While the model did not fully reproduce width and length, the model efficiency to simulate EG volume was satisfactory for both calibration and testing phases, supporting the watershed management objectives of the model. GSA revealed that the most sensitive factors were EG depth, critical shear stress, headcut detachment exponent coefficient b, and headcut detachment leading coefficient a. For EG outputs the model was additive, showing low sensitivity to interactions between the inputs. Prediction of EG spatial evolution on conservation tillage systems requires improved development of gully erosion components, since many of the processes were developed originally for traditional tillage practices or larger channel systems. Our results identify the need for future research when EG form within conservation tillage systems, in particular to study gully headcut, soil erodibility, and width functions specific to these practices.     

甘肃阿尔金南缘白石头沟石墨矿地质特征、成矿条件及找矿标志

甘肃白石头沟石墨矿位于阿尔金南缘敦煌地块,赋存于前寒武纪敦煌岩群大理岩和石英片岩之中,目前圈定矿体33条,主要矿体2条。作为研究白石头沟石墨矿理想地层的敦煌岩群,是一套以变质碎屑沉积岩和变质基性岩为主的变质岩浆杂岩。本文从矿床角度出发,立足于区域地质勘查资料,结合前人研究成果,在对白石头沟石墨矿成矿地质背景、矿床及矿体特征、组合样化学分析、矿石矿物赋存状态及特征研究的基础上,对矿床的成因进行初步探讨并归纳区域找矿标志。研究表明,白石头沟石墨矿可分为大理岩型和石英片岩型两种类型,是古元古代经历区域动力热液变质作用而形成的沉积变质型矿床,成矿物质主要来源于变质碎屑沉积岩类的原岩（海相陆源碎屑岩和碳酸盐岩）本身,成矿环境为古老活动大陆边缘。找矿标志具有特定层位、岩性、矿化及物探特征。     

High resolution facies architecture and digital outcrop modeling of the Sandakan formation sandstone reservoir,Borneo:Implications for reservoir characterization and flow simulation

Advances in photogrammetry have eased the acquisition of high-resolution digital information from outcrops, enabling faster, non-destructive data capturing and improved reservoir modeling. Geocellular models for flow dynamics with in the virtual outcrop in siliciclastic deposits at different sets of sandstone facies architecture remain, however, a challenge. Digital maps of bedding, lithological contrast, spatial-temporal variations of bedding and permeability characteristics make it more easy to understand flow tortuosity in a particular architecture. An ability to precisely model these properties can improve reservoir characterization and flow modeling at different scales. Here we demonstrate the construction of realistic 2 D sandstone facies based models for a pragmatic simulation of flow dynamics using a combination of digital point clouds dataset acquired from LiDAR and field investigation of the Sandakan Formation, Sabah, Borneo.Additionally, we present methods for enhancing the accuracy of outcrop digital datasets for producing high resolution flow simulation. A well-exposed outcrop from the Sandakan Formation, Sabah, northwest Borneo having a lateral extent of 750 m was chosen in order to implement our research approach. Sandstone facies and its connectivity are well constrained by outcrop observations, data from air-permeability measurements, bilinear interpolation of permeability, grid construction and water vector analysis for flow dynamics.These proportions were then enumerated in terms of static digital outcrop model(DOM) and facies model based on sandstone facies bedding characteristics. Flow simulation of water vector analysis through each of the four sandstone facies types show persistent spatial correlation of permeability that align with either cross-bedded orientation or straight with more dispersion high quality sandstone(porosity 21.25%-41.2%and permeability 1265.20-5986.25 mD) and moderate quality sandstone(porosity 10.44%-28.75% and permeability 21.44-1023.33 mD). Whereas, in more heterolithic sandstone(wavy-to flaser-bedded and bioturbated sandstone), lateral variations in permeability show spatially non-correlated patterns over centimeters to tens of meters with mostly of low quality sandstone(porosity 3.4%-12.31% and permeability < 1 mD to 3.21 mD). These variations reflect the lateral juxtaposition in flow dynamics. It has also been resulted that the vertical connectivity and heterogeneities in terms of flow are mostly pragmatic due to the interconnected sandstone rather than the quality of sandstone.     

How soil texture,channel shape and cross-sectional area affect moisture dynamics and water loss in irrigation channels

To enhance the utilization efficiency of farmland irrigation water and reduce the leakage of water conveyance channels, the leakage process of channels was simulated dynamically. The simulated results were compared with data measured in laboratory experiments, and the performance of the model was evaluated. The results indicated that the simulated values of the model were consistent with the observation values, and the R² values varied between 0.91 and 0.99. In addition, based on the laboratory experiments, a water supply system (Mariotte bottles) and soil box were built using plexiglass. Three influencing factors, namely, the channel form, soil texture and channel cross-sectional area, were varied to observe and calculate the resulting cumulative infiltration amount, infiltration rate and wetting front migration distance. HYDRUS-3D software was used to solve the three-dimensional soil water movement equation under different initial conditions. The results demonstrated that the U-shaped channel was more effective than the trapezoidal channel in increasing the utilization efficiency of the water resources. A U-shaped channel with a small channel cross-sectional area should be adopted and the soil particle size should be prioritized in the construction of water conveyance channels for farmlands. The simulation results were in agreement with the observed results, which indicates that HYDRUS-3D is a reliable tool that can accurately simulate the soil moisture movement in water conveyance channels. The research results can provide a reference for the design and operation of farmland irrigation systems.     

Changes in run‐off and sediment load in the three parts of the Yellow River basin,in response to climate change and human activities

Hydrological regimes in the Yellow River have changed significantly because of climate change and intensive human interventions. These changes present severe challenges to water resource utilization and ecological development. Variation of run‐off, suspended sediment load (SSL), and eight precipitation indices (P1: 0–12 mm·day^?1, P12: 12–25 mm·day^?1, P25: 25–50 mm·day^?1, P50: P ≥ 50 mm·day^?1 and corresponding rainfall day: Pd1, Pd12, Pd25, Pd50 day year^?1) in three critical parts of the Yellow River basin (source region: SRYRB, upper reaches: URYRB, middle reaches: MRYRB) were investigated for the period from 1960 to 2015. The results show that run‐off and SSL significantly decreased (P < 0.01) in the URYRB and the MRYRB, whereas their decline in the SRYRB was insignificant (P > 0.05). Moreover, run‐off in the URYRB had one change point in 1987, and SSL in the URYRB as well as run‐off and SSL in the MRYRB had two change points (in the 1970s and the 1990s). Over the same period, only Pd1 and Pd12 in the SRYRB showed significant increasing trends, and an abrupt change appeared in 1981. The optimal precipitation indices for assessing the effects of precipitation on run‐off and SSL in the URYRB and MRYRB were Pd50 and P12, respectively. A double‐mass curve analysis showed that precipitation and human activities contributed to approximately 20% and 80% of the reduction in run‐off, respectively, for both the SRYRB and the MRYRB. However, the contribution rate of precipitation and human activities on SSL reduction was approximately 40% and 60% in the URYRB and 5% and 95% in the MRYRB, respectively. Human activities, primarily soil and water conservation measures and water extraction (diversion), were the main factors (>50%) that reduced the run‐off. However, the dominant driving factors for SSL reduction were soil and water conservation measures and reservoir interception, for which the contribution rate was higher than 70% in the MRYRB. This work strengthens the understanding of hydrological responses to precipitation change and provides a useful reference for regional water resource utilization.     

Dynamics of coastline changes in Mexico

Journal of Geographical Sciences - The goal of our work was to locate and quantify changes that occurred in 66% of the Mexican coastline, based on four land cover maps generated by the Mexican...     

Dynamic metabolite alterations of Portunus trituberculatus during larval development

Journal of Oceanology and Limnology - A mass mortality often occurs from molting to the megalopa stage during the larval development of the swimming crab Portunus trituberculatus. Larvae with...     

基于模糊物元模型的中国旅游生态安全评价及障碍因子诊断研究

基于DPSIR模型构建旅游生态安全评价指标体系,利用模糊物元模型对中国31个省（市、区）（不含港澳台）旅游生态安全进行动态评价,并运用空间自相关分析空间格局演化特征。同时借助障碍度模型,对旅游生态安全的障碍因子进行诊断。结果表明:① 旅游生态安全呈现出波动增长的“W”型演化趋势。2013—2016年中国旅游生态安全在空间上呈现出“东部高、西部低”的分布格局,但随着时间推移,出现“北部高、南部低;中间高、两边低”的格局变化;② 从全局来看,2013—2017年中国旅游生态安全在空间上呈现出显著的空间集聚分布的特点,但集聚程度有逐渐下降的态势。从局部关联来看,各省旅游生态安全空间分布存在着空间集聚特征和省域间的空间依赖性;③ 各省旅游生态安全障碍因子存在显著差异,障碍度高于10%的障碍因子较多,主要的障碍因子有旅游经济密度、游客密度、烟尘排放、生活垃圾处理率和污水处理率等。因此,在大力发展旅游业时,需充分考虑经济发展程度和旅游生态安全提升能力;同时还要注意旅游政策与环境保护政策的协调性。     

BS-ACEBOC: a generalized low-complexity dual-frequency constant-envelope multiplexing modulation for GNSS

GPS Solutions - In order to satisfy the need for combining signals in a constant-envelope modulation, we propose a new dual-frequency constant-envelope modulation (DCEM), called asymmetric...