地理信息系统安全设计     

杨华先  洪亮  魏忠  闵振毅 《地理空间信息》2006,4(6):8-11

针对地理信息系统的安全隐患,从地理信息系统安全的结构层次分析入手,从网络安全、系统安全、数据安全和用户权限四个方面提出了解决地理信息系统安全隐患的策略。  相似文献   

全球海平面变化研究新进展   总被引：9，自引：1，他引：8  

吴涛  康建成  王芳  郑琰明 《地球科学进展》2006,21(7):730-737

综述了近10年来海平面变化研究的主要成果,分析了影响海平面变化的主要因素,探讨了海平面变化研究中存在的一些问题。结果表明：①近10年全球平均海平面上升幅度大约为2.5~3.84 mm/a,热膨胀是引起海平面上升的主因;②海平面变化具有时空分布差异——西太平洋和东印度洋地区上升最快,其值高出全球平均值的10倍以上;大西洋与太平洋30~40°N地区季节变化最明显;③将海平面季节高值时段与北半球热带气旋出现时间进行对比,发现每年8~10月份,在20~50°N的西北太平洋与北大西洋沿岸地区出现海平面最高值与热带气旋相叠加的全球危险海岸带,该地带包括中国大陆东部、日本沿海地区、美国东部海岸带、墨西哥湾地区和加勒比海地区。  相似文献   

Impacts of confining pressure and safety thickness on water and mud inrush in weathered granite     

Jinquan Liu  Weizhong Chen  Zhiping Deng  Taogen Liu 《Marine Georesources & Geotechnology》2020,38(2):144-153

Abstract

Due to the strong disintegration and water erosion of completely weathered granite, water and mud inrush disasters are apt to take place in this zone during underwater tunnel construction. The pore, compactness, seepage path length, fracture geometries and their interconnections for water and mud transfer are strongly influenced by confining pressure and waterproof-resistant slab safety thickness. In order to inspect the influence, a series of experiments based on a self-designed testing system and non-Darcy testing method were performed. The results indicated that the water and mud inrush evolution increased with the increase of confining pressure and decreased with the increase of safety thickness. In particular, the confining pressure mainly influences the initial evolution stage, and a critical safety thickness to prevent water and mud inrush is obtained. Besides, the non-Darcy testing method results shows that the water and mud inrush evolution affects the influence of non-Darcy flow. For example, while the safety thickness was smaller than the critical value, the evolution was large and unstable and its behavior transferred into nonlinear. In this case, the flow changed to non-Darcy flow.  相似文献   

粤东南澳岛青澳海滩侵蚀退化风险评价及其安全调控          下载免费PDF全文

李平  杜军  张志卫  徐国强 《海洋科学进展》2020,38(1):171-181

分析了南澳岛海滩资源储量、空间分布及其开发利用现状,开展海岛海滩侵蚀风险评价,选择青澳海滩开展岸滩及其海湾海床地形、沉积物、动力泥沙调查,分析探讨了青澳海滩泥沙动力沉积特征,灾变退化过程机制,并从海滩稳定性和游客安全角度给出安全调控建议。结果表明:1)南澳岛海滩资源储量与侵蚀风险区域分异特征明显,其中青澳海滩旅游活动频繁、开发强度大,侵蚀退化风险等级高,人为破坏干扰抑制滩海泥沙交换,无序无度占滩开发与利用破坏了海滩自然演化进程,短期过量旅游活动加速海滩侵蚀退化进程;2)青澳湾沉积物以粗粒砂为主,沙源供给不足,不同岸段岸线进退与岸滩蚀淤与海滩方位、波浪动力强度强弱关系密切,具有明显的纵向沉积地貌分带特征。湾内落潮优势流(SE)优于涨潮(NW),对泥沙输运进入湾内具有抑制作用,潮周期海湾泥沙自湾内向湾外输运,泥沙以外输为主单宽输沙为3 400 t;3)青澳海滩存在严重的"无序占滩建筑,污水肆意排放,管理不规范"等问题,监测评价亦表明侵蚀退化风险巨大,游客安全面临着风险隐患,建议青澳海滩实行以生态化养护开发和"游客为中心"为理念的安全调控措施,设立红线及安全标示。该研究为岛礁生态建设、海岛保护及修复提供科学依据。  相似文献   

社区生活圈的新时间地理学研究框架   总被引：5，自引：5，他引：0  

柴彦威  李春江  张艳 《地理科学进展》2020,39(12):1961-1971

社区生活圈从居民日常活动及行为视角考察城市社区,是城市地理学和城市相关学科的研究前沿,也是中国国土空间规划体系创新的重要组成部分,以及中国城市社会可持续发展的重要抓手。伴随着流动性和信息化的不断深入,社区生活圈的主体日益多元化、社区活动和居民时空行为日益多样化、社区空间的功能与意义日益丰富化,亟需城市地理学的研究创新与实践引导。时间地理学是理解人与环境关系的社会—技术—生态综合方法,为早期基于时空行为与生活空间的社区生活圈研究提供了重要基础。新时间地理学重视家庭及其他组织企划的交互与时空组合,可为社区生活圈内个体—家庭—社区之间的复杂互动关系研究、时空行为的社会文化制约与多情境分析及模拟提供重要支撑。论文基于新时间地理学方法,从理论、方法和实证3个维度提出社区生活圈的新时间地理学研究框架,具体包括构建社区生活圈的时空行为理论,揭示社区生活圈的时空间结构;创新社区生活圈的时空行为分析和模拟方法;从社区生活圈时空行为优化、社区交往生活圈、社区安全生活圈等方面创新中国城市规划与管理等研究内容。  相似文献   

The 2019 Brumadinho tailings dam collapse: Possible cause and impacts of the worst human and environmental disaster in Brazil     

《International Journal of Applied Earth Observation and Geoinformation》2020

On 25th January 2019, the tailings dam of the Brumadinho iron mine operated by Vale S/A failed catastrophically. The death toll stood at 259 and 11 people remained missing as of January 2020. This tragedy occurred three years after Mariana’s tailings dam rupture – the most significant tailing dam disaster in Brazilian history. Thus far, a systematic investigation on the cause and effect of the failure has yet to be conducted. Here, we use satellite-driven soil moisture index, multispectral high-resolution imagery and Interferometric Synthetic Aperture Radar (InSAR) products to assess pre-disaster scenarios and the direct causes of the tailings dam collapse. A decreasing trend in the moisture content at the surface and the full evanescence of pond water through time (2011–2019) suggest that the water was gradually penetrating the fill downwards and caused the seepage erosion, saturating the tailings dam. Large-scale slumping of the dam (extensional failure) upon the rupture indicates that the materials of the fill were already saturated. InSAR measurements reveal a dramatic, up to 30 cm subsidence in the dam (at the rear part) within the past 12 months before the dam collapse, signifying that the sediments had been removed from the fill. Although the information on the resistance level of the tailings dam to infiltrations is not available, these pieces of evidence collectively indicate that the seepage erosion (piping) is the primary cause for the chronic weakening of the structure and, hence, the internal “liquefaction” condition. Upon the collapse, the fully saturated mud tailings flowed down the gentle slope area (3.13 × 10⁶ m²), where 73 % were originally covered by tree, grass or agricultural tracts. The toxic mud eventually reached the Paraopeba River after travelling 10 km, abruptly increasing the suspended particulate matter (SPM) concentration and the toxic chemical elements in the river, immediately affecting the local livelihoods that depend on its water. The Paraopeba River is a major tributary of the San Francisco River, the second-longest river in Brazil reaching the Atlantic Ocean. We anticipate that the environmental repercussions of this toxic seepage will be felt throughout the entire basin, especially riverine communities located downstream.  相似文献   

Possible impact of dam reservoirs and river diversions on material fluxes to the Gulf of Thailand   总被引：1，自引：0，他引：1  

Manuwadi Hungspreugs  Wilaiwan Utoomprurkporn  Penjai Sompongchaiyakul  Watanee Heungraksa 《Marine Chemistry》2002,79(3-4)

Thai people have always been agricultural-based, although rainwater is not enough to sustain year-round agricultural practice. The first earth-filled dam was built across a valley near Sukhothai over 700 years ago. Now, there are six major multipurposed dam reservoirs, among which the largest is the Sri Nakarind (SN) built across the Kwae Yai River, the main branch of the Mae Klong River in the western part of Thailand. The first multipurposed dam reservoir built on the Chao Phraya (largest) River System is the Bhumibhol Dam on the Ping River. In this paper, the two Mae Klong River Dam Reservoirs and their biology and chemistry are discussed. Also investigated are the historical records of material fluxes to the Gulf of Thailand in down-core sediment profiles and in 40-year bands of coral, Porites lutea, taken from the Upper Gulf of Thailand near Si Chang Island. Sediment cores studied did not show clear decreases in the biogenic silica concentration in the Upper Gulf area after the building of dams. Part of the reasons might be the higher rate of dissolution of silica in tropical waters bioturbation of surface layers or the constant disturbance of the bottom sediment by fishermen using bottom trawls. The record in the coral bands seems to be more promising in reflecting the material flux change due to dam construction. An attempt to detect changes in diatom population with time due to the expected decrease in siliceous material discharge was not possible because there was a change from the use of 70 μm mesh size to 20 μm mesh size resulting in the increase of species and biomass, although the diatom percentage remained above 80% in all estuarine samples.  相似文献   

福建沿岸海域浒苔藻类的营养成分含量与食用安全   总被引：4，自引：0，他引：4  

林建云  陈维芬  贺青  林力斌  汤荣坤  暨卫东 《台湾海峡》2011,30(4):570-576

对福建沿岸海域浒苔（Enteromorpha）样品的主要组成成分、氨基酸、脂肪酸、矿物质含量的研究表明,浒苔属高膳食纤维（49．0％～59．1％）、高蛋白质（19．60％～38．24％）、低脂肪（0．20％～0．55％）的藻类．浒苔中17种氨基酸总量（Ctaa）与蛋白质含量的比值为74．1％～91．0％;其必需氨基酸含量（Ctaa）占C11从的35．4％～40．0％,CⅢ与非必需氨基酸含量（C。Ⅲ）之比为0．55～0．67,且呈味氨基酸的含量丰富（47．1％）,氨基酸组成均衡．浒苔油脂中脂肪酸组成丰富,n一3PUFA含量达油脂总量的20．0％～26．4％,其中含有EPA、DHA．浒苔中矿物质含量较高,尤其富含镁、钙、铁、锌、硒、钾等人体必需矿物元素．有害元素测定结果表明,中、低潮区浒苔的铅、汞、镉、砷含量均能够符合《无公害食品海藻》安全指标的限量要求,养殖区、高潮区部分浒苔的Pb含量超标．研究结果认为,在低污染海区生长的浒苔是一种高蛋白质、高膳食纤维、低脂肪、矿物元素丰富且安全的海洋食品．  相似文献   

世界水产品绿色养殖比较研究及对中国启示          下载免费PDF全文

刘华楠  赵昕怡 《海洋开发与管理》2022,39(3):51-55

当前全球渔业捕捞量已接近顶峰局势,水产养殖发展面临巨大环境压力,水产品绿色养殖能满足消费者对优质蛋白需求的同时,还能有效缓解生态问题,保证食品质量安全。水产品养殖绿色发展已成为世界各国的共识,渔业发达国家在一定程度上已形成较完善的绿色水产养殖体系。文章基于全球水产业发展现状和趋势,通过研究欧盟、美国和日本水产品绿色养殖的相关经验,最后结合中国水产养殖业发展现状,提出在建立严格认证标准的基础上,国内政府应加强对“绿色水产品”消费的正确引导;借鉴别国对渔业可持续发展的政策和管理制度;注重关键科学技术的研发,做到产学结合;保障资金的有效投入等相关政策建议。  相似文献   

Properties of geogrid-reinforced marine slope due to the groundwater level changes     

Ramin Vali  Jie Li  Gholamreza Shams  Pieter van Gelder 《Marine Georesources & Geotechnology》2018,36(6):735-748

Evaluation of slope stability, especially in the absence of a proper bed such as marine soils, is one of the most important issues in geotechnical engineering. Using geogrid layers to enhance the strength and stability of embankments is regarded as a commendable stabilization method. On the other hand, groundwater level erratically fluctuates in coastal areas. Therefore, the aim of this research is to study the effects of groundwater level changes on stability of a geogrid-reinforced slope on loose marine soils in Qeshm Island, Iran. At first, geotechnical properties of the site were obtained by comprehensive series of geotechnical laboratory and in situ tests. Then, by simultaneous changes of groundwater level and several parameters such as embankment slope, loading, geogrid length, geogrid number, and tensile strength of geogrid, different characteristics such as embankment safety factor (SF), vertical and horizontal displacements at embankment top and embankment base were studied. It was observed that groundwater level had significant effects on behavior of the embankment. For most of the observations, by decreasing the groundwater level, the displacements decreased and consequently safety factor increased. Increasing the length, number, and tensile strength of geogrid led to the reduction of displacements and an increase in the safety factor.  相似文献