Safety of small and medium dams in permafrost regions

Safe operation and performance of dams is one of the key issues in permafrost regions. At present, the existing dams are 40–45 years old and they are reaching their design life limit. Intensive geocryological processes（thermokarst, thermal erosion, frost heaving, suffosion, concentrated seepage along the voids left by melt ice and others） begin to develop at the early stages of construction. These processes are even more intensive under severe climatic conditions of the permafrost zone due to the large thermal and moisture gradients and the resulting complex thermal stress-strain state in the structures. Determining safety criteria is a critical and difficult task in dam safety management. The existing procedures need to be continuously refined and improved depending on dam importance class. Some researchers recommend introducing process development criteria（stability, destabilization, and extremality） for more objective assessment of dam safety, in addition to the existing two condition criteria. In other words, they call for a multi-factor dam – environment interaction system. A case study of safety declaration for an existing dam is presented.     

小区域癌症数据典型空间插值方法比较研究

癌症已成为危害全球居民健康的重大民生问题,选取合适的空间插值方法分析小区域癌症数据的空间特征可对区域性癌症防控工作的有效开展提供依据.本研究以湖南省苏仙区2012和2016年以村为单位的肺癌死亡率数据为研究对象,以平均误差和均方根误差为评价指标,对反距离加权(IDW)、普通克里金(OK)、趋势面分析(TSA)、多元线性...     

Nocturnal hypothermia and its energetic significance for small birds living in the arctic and subarctic regions. A review

Nocturnal hypothermia is demonstrated in a number of small northern birds. These birds utilize hypothermia rant among other energy-saving mechanisms and lower the body temperature by some 10°C. In most bird species hypothermia is utilized only in conjunction with a state of inanition. However, hypothermia has also been demonstrated in birds with satisfactory feeding conditions and body weight. For none of the small northern birds utilizing nocturnal hypothermia, is inanition necessary for the induction of a state of hypothermia. A seasonal effect on the hypothermic response has been demonstrated for two species of tits, the black-capped chickadee Parus atricapillus and the willow tit Parus montanus , and also for an Andean hummingbird. The depth of hypothermia achieved significantly and linearly was correlated with the ambient temperature for the same two species of tits. By the use of nocturnal hypothermia, birds living in temperate zones can save as much as 75% of their energetic costs, compared with their energy consumption at normal body temperature. The reduction in the nightly expenditure of energy is considerable also in small-sized arctic and subarctic birds that utilize nocturnal hypothermia. The saving of energetic costs may easily represent the margin between life and death for such small birds living under the combined stresses of hunger, cold and long nights.     

Stable regions in the Earth's liquid core

Summary. Slow cooling of the whole Earth can be responsible for the convection in the core that is required to generate the magnetic field. Previous studies have assumed the cooling rate to be high enough for the whole core to convect. Here we study the effects of a low rate of cooling by assuming the temperature at the base of the mantle to remain constant with an initially entirely molten, adiabatic core. We argue that, in such a situation, convection would stop at the top of the core, and calculate the consequent thermal evolution. A stable, density stratified layer grows downwards from the core mantle boundary reaching a thickness of 100–1000 km in a few thousands of millions of years. There is some geomagnetic evidence to support belief in the existence of such a stable layer.     

Advances in thermokarst lake research in permafrost regions

A thermokarst lake is defined as a lake occupying a closed depression formed by ground settlement following thawing of ice-rich permafrost or the melting of massive ice. As it is the most visible morphologic landscape developed during the process of permafrost degradation, we reviewed recent literature on thermokarst studies, and summarized the main study topics as： development and temporal evolution, carbon release, and ecological and engineering influence of thermokarst lakes. The climate warming, forest fires, surface water pooling, geotectonic fault and anthropogenic activity are the main influencing factors that cause an increase of ground temperatures and melting of ice-rich permafrost, resulting in thermokarst lake formation. Normally a thermokarst lake develops in 3–5 stages from initiation to permafrost recovery. Geo-rectified aerial photographs and remote sensing images show that thermokarst lakes have been mainly experiencing the process of shrinkage or disappearance in most regions of the Arctic, while both lake numbers and areas on the Qinghai-Tibet Plateau have increased. Field studies and modeling indicates that carbon release from thermokarst lakes can feedback significantly to global warming, thus enhancing our understanding of the influences of thermokarst lakes on the ecological environment, and on regional groundwater through drainage. Based on field monitoring and numerical simulations, infrastructure stability can be affected by thermal erosion of nearby thermokarst lakes. This review was undertaken to enhance our understanding of thermokarst lakes, and providing references for future comprehensive studies on thermokarst lakes.     

旅游创新演进之路:从企业创新到区域创新

旅游创新认知误区极大限制了研究者对旅游创新规律的探索。在反思旅游创新研究的前提下,分析了旅游创新认知误区的形成原因与修正路径,研究了由库克旅行社创建所引发的旅游企业创新崛起之路,并对区域旅游创新演进的基础与创新演进的动力进行了探索,旨在还原旅游创新实践的真实面目,以推动旅游创新研究的深入。     

Paleohydrology inferred from diatoms in northern latitude regions

Several recent studies have successfully applied diatom-based paleolimnological techniques to infer past hydrological changes in arctic and subarctic regions. For example, we summarize arctic studies that attempt to determine changes in peat water content, flood frequency, river discharge, effective moisture and ice cover in northern regions. Some of the investigations are still in preliminary stages, but represent innovative approaches to study arctic and subarctic paleohydrology. New data demonstrate that lake depth, which may be related to changing hydrological conditions, is a significant variable influencing the distributions of diatom taxa in lake surface sediment calibration sets from Wood Buffalo National Park (WBNP), on the border of Alberta and the Northwest Territories, Canada, and from Fennoscandia (mainly northwest Finland). Weighted averaging regression and calibration methods were used to develop quantitative inference models for lake depth using diatom assemblages preserved in surface sediments. The predictive abilities of the transfer functions were relatively high (for WBNP r² = 0.70 and RMSE = 2.6 m, and for Fennoscandia r² = 0.88 and RMSE = 1.8 m). However, evaluating the transfer functions using jack-knifing procedures indicated lower predictive abilities, possibly reflecting the relatively small sample size and/or short gradients used in these calibration sets. Such transfer functions can be used to track overall trends in lake levels, and provide an objective assessment as to directions of changing lake levels. Any interpretations of inferred lake levels, especially those related to climate change, must be made cautiously and must include some understanding of the local, present-day hydrological system.     

Gravitational Seismodislocations in Mountainous regions of Southeastern Kazakhstan

Data on rock falls and landslides caused by strong earthquakes in the Zhetysu Alatau, Ile Alatau, Kungei Alatau and Teriskei Alatau mountain ranges on the territory of Southeastern Kazakhstan are presented. The study revealed more than 60 large seismogenic rock falls and landslides, the volume of 25 of them varies from 10 to 100 mil. m³, and the volume of the four largest exceeds 100 mil. m³. The volume of the largest rock fall in the valley of the Ulken Almaty river in the Ile Alatau mountain range is estimated at 380 mil. m³. The highest density of seismogenic landslides was recorded in the low-mountain zone of the northern slope of the Ile Alatau range where the magnitude 9 earthquake of 1887 caused a massive formation of landslides with the volume totaling more than 400 mil. m³ and a density of 1/5 km². The proportion of landslide-affected areas is estimated at 5% of the area of their occurrence. In the mid- and high-mountain zones of Zhetysu, Ile and Kungei Alatau, the density of seismogenic rock falls varies from 1/100 to 1/50 km², and the proportion of rock fall-affected areas varies from 1 to 1.5%. It is found that seismogenic rock falls have dammed 26 lakes, and the volume of nine such lakes exceeds 10 mil. m³. The largest rock fall-affected lakes is Upper Zhasylkol in the valley of the Aganakty river in Zhetysu Alatau with the volume of 44 mil. m³. Data from earthquake catalog were used to compile the map for the recurrence frequency of earthquakes of magnitude higher than 6, capable of causing seismogenic rock falls and landslides. It is found that during the last 130 years, in Ile and Kungei Alatau such earthquakes recurred four times. It is established that earthquakes with maximum magnitude 9 are possible in the mountainous regions of Southeastern Kazakhstan.     

Contrasting climate change in the two polar regions

The two polar regions have experienced remarkably different climatic changes in recent decades. The Arctic has seen a marked reduction in sea-ice extent throughout the year, with a peak during the autumn. A new record minimum extent occurred in 2007, which was 40% below the long-term climatological mean. In contrast, the extent of Antarctic sea ice has increased, with the greatest growth being in the autumn. There has been a large-scale warming across much of the Arctic, with a resultant loss of permafrost and a reduction in snow cover. The bulk of the Antarctic has experienced little change in surface temperature over the last 50 years, although a slight cooling has been evident around the coast of East Antarctica since about 1980, and recent research has pointed to a warming across West Antarctica. The exception is the Antarctic Peninsula, where there has been a winter (summer) season warming on the western (eastern) side. Many of the different changes observed between the two polar regions can be attributed to topographic factors and land/sea distribution. The location of the Arctic Ocean at high latitude, with the consequently high level of solar radiation received in summer, allows the ice-albedo feedback mechanism to operate effectively. The Antarctic ozone hole has had a profound effect on the circulations of the high latitude ocean and atmosphere, isolating the continent and increasing the westerly winds over the Southern Ocean, especially during the summer and winter.     

Rainfall partitioning by desert shrubs in arid regions

We measured the rainfall partitioning among throughfall, stemflow, and interception by desert shrubs in an arid region of China, and analyzed the influence of rainfall and canopy characteristics on this partitioning and its ecohydrological effects. The percent-ages of total rainfall accounted for by throughfall, stemflow, and interception ranged from 78.85±2.78 percent to 86.29±5.07 per-cent, from 5.50±3.73 percent to 8.47±4.19 percent, and from 7.54±2.36 percent to 15.95±4.70 percent, respectively, for the four shrubs in our study (Haloxylon ammodendron, Elaeagnus angustifolia, Tamarix ramosissima, and Nitraria sphaerocarpa). Rain-fall was significantly linearly correlated with throughfall, stemflow, and interception (P < 0.0001). The throughfall, stemflow, and interception percentages were logarithmically related to total rainfall (P < 0.01), but were quadratically related to the maximum 1-hour rainfall intensity (P < 0.01). The throughfall and stemflow percentages increased significantly with increasing values of the rainfall characteristics, whereas the interception percentage generally decreased (except for average wind speed, air temperature, and canopy evaporation). Regression analysis suggested that the stemflow percentage increased significantly with increasing crown length, number of branches, and branch angle (R2 = 0.92, P < 0.001). The interception percentage increased significantly with increasing LAI (leaf area index) and crown length, but decreased with increasing branch angle (R2 = 0.96, P < 0.001). The mean funnelling percentages for the four shrubs ranged from 30.27±4.86 percent to 164.37±6.41 percent of the bulk precipitation. Much of the precipitation was funnelled toward the basal area of the stem, confirming that shrub stemflow conserved in deep soil layers may be an available moisture source to support plant survival and growth under arid conditions.     

Demographic transition in small countries

Half of the world's 200 countries have less than 3.37 million inhabitants, and many of these small countries are often assumed to experience rapid demographic transition. This is true of many of the small island populations of the developing world, especially those with largely immigrant and pluralistic populations, unusual family structures, and rapid economic development. Smallness of population alone, however, is not sufficient to ensure rapid demographic transition and many small countries of mainland Africa have experienced little transition.     

极地航空重力测量及其应用进展

在论述航空重力测量技术在目前重力场信息获取中不可替代性的基础上,回顾并简述了国际、国内航空重力测量技术的发展历史,介绍了航空重力测量的基本原理,总结了航空重力测量技术在极地航空地球物理勘探任务中的应用。指出航空重力测量技术是目前唯一兼顾高精度高分辨率并且能覆盖全南极区域的观测手段,在完善南极地区全球重力场模型、研究南极地区地质构造、质量变化等任务中起着非常重要的作用。     

区域协同创新对创新绩效的影响机制研究

区域协同创新有利于促进区域间创新要素流动,优化科技资源的合理配置,提升区域创新绩效。采用改进的DEA模型,在测度中国62个城市2003～2016年创新绩效的基础上,运用门槛回归模型分析在不同经济发展水平条件下区域协同创新对创新绩效的影响机制。结果表明:①研究期内62个城市的创新绩效整体上在波动中稳步提升,区域创新绩效存在较大的空间非均衡性。②区域协同创新对于区域创新绩效的提升具有促进作用,区域创新绩效与区域协同创新核心解释变量之间存在着非线性关系,专利合作数对区域创新绩效的影响呈现正向双门槛特征,科技论文合作数对区域创新绩效的影响呈现正向单门槛特征,两者对区域创新绩效的影响都随着经济发展水平的提升呈现出不同程度的下降趋势。③科技人员流动量在跨过经济发展水平第一门槛10.088而低于第二门槛10.255时,对创新绩效的促进作用最明显;科技资金流动量在经济发展水平第一门槛9.427以下时对创新绩效的影响最显著。     

中国各省区经济增长溢出分析

本文基于新增长理论,考虑空间相互作用的衰减性和溢出与GDP缺口的关系,改进了Conley、Ligon(2003)建立的区域溢出统计分析模型。基于这个模型,计算分析了中国各省区的GDP溢出。分析表明:中国大部分省区的增长溢出是正的,上海对外的增长溢出最大。在中国中部地区,湖北省具有重要的溢出作用。中国西部地区除云南、新疆外,经济溢出基本上是负的。因此推广它们的经验,促进西部经济与东部一体化是重要的发展战略。分析还建议,将给予新疆的某些政策也给予东北地区,可能是振兴东北老工业基地的有效措施。     

Spatiotemporal distribution characteristics of the fog regions in China

The spatial distribution and monthly/annual variation of foggy days in China are analyzed based on the monthly mean fog data collected from 604 observational stations for the period 1961–2000. Results show that there are six fog regions in China: the middle reaches of the Yangtze River, coastal areas, Yunnan-Guizhou Plateau, eastern Gansu–Shaanxi region, Huaihe River valley, Tianshan mountainous area and northern Xinjiang. On the whole the interannual variation trend of foggy days is descending, especially an obvious decline after the 1980s. The areas where the foggy days have obvious tendency present a southwest-northeast direction. The rising trend regions alternate with descending trend regions, forming a SE-NW directional wave structure. In general, the number of foggy days in autumn and winter is larger than in spring and summer over most fog regions. The monthly variation curves of foggy days are bimodal in the coastal area of the Yellow Sea and northern Xinjiang, and unimodal in other regions.     

中国雾区的分布及其季节变化

1 Introduction Fog is a weather phenomenon that horizontal visible distance is reduced within 1 km by plenty of water drops and particles of ice crystal. It not only has unfavorable influence on the traffic of water, land and air, but also brings serious …