就医空间可达性分析的两步移动搜索法——以江苏省东海县为例   总被引：8，自引：5，他引：3  

胡瑞山  董锁成  胡浩 《地理科学进展》2012,31(12):1600-1607

精确评价医疗设施可达性的空间分异样状况是合理配置医疗资源的前提。本文在回顾国内外关于医疗空间可达性研究的基础上, 采用两步移动搜索法, 以江苏省贫困县--东海县为案例, 以行政村和医院为分析单元, 基于迪卡斯特拉算法计算出各村到医院(卫生院)的最短通行时间, 进而分析各村医疗空间可达性分异情况。采用不用服务时间阈值范围进行空间敏感性分析, 综合研判缺医地区分布特点。与传统的医卫人员和人口比值的方法相比, 两步移动搜索法能有效显示县域范围内医疗可达性的空间分异情况。采用较大的时间阈值, 医疗空间可达性分异较为平滑, 采用较小服务阈值则空间分异显著, 缺医范围也较大。东海县医疗空间可达性整体呈单核结构, 并沿主要交通线延伸, 缺医地区多分布于边缘乡镇。提高边缘乡镇的行政村的甲级卫生院等级和乡村道路等级将会改善边缘乡镇的就医可达性。  相似文献   

中山市交通系统地震易损性分析     

杜鹏  聂树明  吴英琴  李晋 《华南地震》2010,30(4):48-54

交通系统地震易损性分析主要是针对系统中的道路、桥梁及路边建筑破坏的影响。分别采用经验统计法、单体桥梁分析方法、瓦砾堆积物计算方法得到了各自对应的道路路段通行概率,而这三个因素共同构成了道路路段的最终通行概率,通过Monte-Carlo算法即可得出交通系统连通可靠性。根据分析结果寻找薄弱环节,为制定相应的防震减灾对策提供依据。  相似文献   

Running safety analysis of a train on the Tsing Ma Bridge under turbulent winds     

Weiwei Guo  He Xia  Youlin Xu 《地震工程与工程振动(英文版)》2010,9(3):307-318

The dynamic responses of the Tsing Ma suspension bridge and the running behaviors of trains on the bridge under turbulent wind actions are analyzed by a three-dimensional wind-train-bridge interaction model. This model consists of a spatial finite element bridge model, a train model composed of eight 4-axle identical coaches of 27 degrees-of-freedom, and a turbulent wind model. The fluctuating wind forces, including the buffeting forces and the self-excited forces, act on the bridge only, since the train runs inside the bridge deck. The dynamic responses of the bridge are calculated and some results are compared with data measured from Typhoon York. The runnability of the train passing through the Tsing Ma suspension bridge at different speeds is researched under turbulent winds with different wind velocities. Then, the threshold curve of wind velocity for ensuring the running safety of the train in the bridge deck is proposed, from which the allowable train speed at different wind velocities can be determined. The numerical results show that rail traffic on the Tsing Ma suspension bridge should be closed as the mean wind velocity reaches 30 m/s.  相似文献   

Determination of scoured bridge natural frequencies with soil–structure interaction     

《Soil Dynamics and Earthquake Engineering》2013

This study developed a finite element method with the effect of soil–fluid–structure interaction to calculate bridge natural frequencies. The finite element model includes bridge girders, piers, foundations, soil, and water. The effective mass above the soil surface was then used to find the first natural frequency in each direction. A field experiment was performed to validate that the natural frequencies calculated using the proposed finite element method had acceptable accuracy. The calculated natural frequencies with the fluid–structure interaction effect are always smaller than those without this effect. However, the frequency change due to the fluid effect is not obvious, so using the soil–structure interaction model is accurate enough in the bridge natural frequency analysis. The trend of the frequency decreases with the increase of the scour depth, but the curve is not smooth because of non-uniform foundation sections and layered soils. However, when the scour depth is such that pile cap is exposed, the changes in natural frequency with the scour depth are more obvious, and this is useful for measurement of the depth using bridge natural frequencies.  相似文献   

Antibiotic resistance of bacteria isolated from shrimp hatcheries and cultural ponds on Donghai Island, China   总被引：1，自引：0，他引：1  

Zhang YB  Li Y  Sun XL 《Marine pollution bulletin》2011,62(11):2299-2307

The resistance of bacteria to 12 different antibiotics was investigated in shrimp farms on Donghai Island, China. Antibiotic-resistant bacteria were found to be widespread in shrimp farms, indicating a high environmental risk. Further, significant differences were found in bacterial strains among farms (ANOVA, p < 0.05), showing resistance to antibiotics such as ampicillin, trimethoprim, compound sinomi, tetracycline, chloramphenicol and cefazolin. No significant differences in antibiotic resistance were found among 6 hatcheries evaluated in this study (ANOVA, p > 0.05), between exalted and traditional shrimp ponds (ANOVA, p > 0.05), and between cultural ponds and corresponding control water source sites (T-test, p > 0.05). In cultural ponds, no significant difference in bacterial resistance to antibiotics was found between water and sediment (T-test, p > 0.05), and antibiotic resistance of bacteria from water showed a significant positive correlation with that from sediment (p < 0.05). Therefore, our study indicates that bacterial multiple antibiotic resistance (MAR) is more widespread in shrimp hatcheries than ponds.  相似文献   

Late glacial and holocene landscapes of central Beringia     

Anatoly V. Lozhkin  Patricia Anderson  Wendy R. Eisner  Tatiana B. Solomatkina 《Quaternary Research》2011,76(3):383-392

New palynological and sedimentological data from St. Lawrence Island present a rare view into late-glacial and Holocene environments of the central Bering Land Bridge. The late glaciation was a time of dynamic landscape changes in south-central Beringia, with active thermokarst processes, including the formation and drainage of thaw lakes. The presence of such a wet, unstable substrate, if widespread, probably would have had an adverse impact on food sources and mobility for many of the large mammal populations. The establishment of Betula shrub tundra on the island suggests late-glacial summers that were warmer than present, consistent with regional paleoclimatic interpretations. However, the increasing proximity to the Bering Sea, as postglacial sea levels rose, modified the intensity of warming and prevented the establishment of deciduous forest as found in other areas of Beringia at this time. The mid- to late Holocene is marked by more stable land surfaces and development of Sphagnum and Cyperaceae peat deposits. The accumulation of organic deposits, decline of shrub Betula, and decrease in thermokarst disturbance suggest that conditions were cooler than the previous. A recent decline in peat accumulation at the study sites may relate to local geomorphology, but similar decreases have been noted for other arctic regions.  相似文献   

Palaeotopography of the northern portion of the Telychian (Silurian) turbidite basin in central Wales     

D.M.D. James 《Geological Journal》2005,40(5):593-601

New palaeocurrent data from the country northeast and southwest of Corris (central Wales) indicate that Telychian sandstones in the Devil's Bridge Formation hereabouts were transported from both the northeast and northwest, consistent with topographical control by down‐to‐southeast movement on the Bala Lineament. This conclusion is supported by considerations of thickness variation and by evidence for listric detachment faulting in the formation at Bwlch y Groes. Towards Plynlimon, flow is broadly southerly and suggests confinement by the northward extension of the Bronnant Fault. A facies and palaeocurrent map is presented for the utilis sub‐Biozone of the Telychian which links with work by the British Geological Survey between Aberyswyth and Rhayader where, by contrast, palaeoflow is to the NNW. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Considering dynamic soil structure interaction (SSI) effects on seismic isolation retrofit efficiency and the importance of natural frequency ratio   总被引：3，自引：0，他引：3  

Edward H. Stehmeyer  III  Dimitris C. Rizos   《Soil Dynamics and Earthquake Engineering》2008,28(6):468-479

This paper utilizes and expands on existing coupled BEM–FEM (finite element method) methods for the investigation of the effects of soil structure interaction (SSI) on both an un-retrofitted and seismically isolated typical bridge structure. A simple numerical model of the bridge and surrounding soil is formulated and excited by an earthquake excitation. Utilizing Newmark's β FEM solution method along with the closed form B-spline BIRF method, the structural damped period, composite damping ratio, pier relative displacement, and base shear demand are monitored. From these results, the effects of SSI on this structure are identified. Additionally, the importance of the relative rigidity between the soil-foundation system and the bridge structure is also investigated. The results of the studies indicate that the response of the complete structure system considered is affected by the inclusion of SSI effects. Furthermore, the efficiency of the isolation measures designed using fixed base conditions is decreased by considering SSI over a certain relative rigidity range that is quantified using the structure to soil-foundation natural frequency ratio.  相似文献   

汶川8.0级地震中几座近断层桥梁失效模式的初步探讨   总被引：4，自引：0，他引：4  

周国良  崔成臣  刘必灯  李小军 《震灾防御技术》2008,3(4):370-378

“5．12”汶川地震造成了多座大型桥梁严重破坏甚至完全垮塌。本文以庙子坪特大桥、百花大桥、小渔洞大桥、石蓑衣大桥、回澜立交桥为例,介绍了结构形式不同的这几座桥梁的破坏模式,初步分析了震害机理。地震动强度过大、强震持续时间过长、近断层特性以及地质灾害等是造成这些桥梁破坏的客观原因;桥梁结构的某些初始缺陷和特殊结构形式导致的受力复杂性是造成地震破坏的主观因素。针对震害特点和破坏机理,本文还探讨了强震区防御桥梁地震破坏应关注的问题。  相似文献   

Seismic response of an urban bridge-support system in soft clay     

Juan M. Mayoral  Yolanda AlbertoManuel J. Mendoza  Miguel P. Romo 《Soil Dynamics and Earthquake Engineering》2009

The numerical simulation of an instrumented urban bridge support and its foundation system was conducted. The bridge works as a deck in a surface subway station and was built 12 yr ago in the so-called Lake Zone in Mexico City, where very soft clays, exhibiting low shear strength and high compressibility prevail. Since the beginning of its construction, pile loads, soil–raft contact pressures and the overall response of the foundation system have been monitored. Within this period, several earthquakes have occurred. Thus, an extensive database of accelerations, pore pressures and load histories have been recorded. In particular, this paper focuses on the bridge response observed during two moderated intensity events, the 2004, 6.3 M_w, Guerrero Coast and the 1999, 7.0 M_w, Tehuacan earthquakes. Finite element models were developed to reproduce the measured responses and to assess the soil–foundation-support performance for long-term conditions, including the effects of potential changes in the dynamic soil properties due to regional subsidence. The computed dynamic responses obtained with the simulation for the free field and structure compares fairly well with the recordings.  相似文献