中国流动人口地域类型——划分方法及空间分布(英文)

With the rapid increase of the number and influence of floating population in China,it is urgently needed to understand the regional types of China’s floating population and their spatial characteristics. After reviewing the current methods for identifying regional types of floating population,this paper puts forward a new composite-index identification method and its modification version which is consisted of two indexes of the net migration rate and gross migration rate. Then,the traditional single-index and the new composite-index identification methods are empirically tested to explore their spatial patterns and characteristics by using China’s 2000 census data at county level. The results show:(1) The composite-index identification method is much better than traditional single-index method because it can measure the migration direction and scale of floating simultaneously,and in particular it can identify the unique regional types of floating population with large scale of immigration and emigration. (2) The modified composite-index identification method,by using the share of a region’s certain type of floating population to the total in China as weights,can effectively correct the over-or under-estimated errors due to the rather large or small total population of a region. (3) The spatial patterns of different regional types of China’s floating population are closely related to the regional differentiation of their natural environment,population density and socio-economic development level. The three active regional types of floating population are mainly located in the eastern part of China with lower elevation,more than 800 mm precipitation,rather higher population densities and economic development levels.     

The study on county accessibility in China: Characteristics and effects on population agglomeration

This paper calculated spatial accessibility of all counties (city, urban district) in China with cost weighted distance method. Region divisions of county accessibility were conducted, and relation of traffic accessibility and population aggregation was discussed in this paper. The results indicated that county accessibility in China had mainly low values and a distribution structure of circle layer and reverse-to-natural gradient. There was an obvious correlation between county accessibility and population density in China. With these analyses, inner mechanisms of population migration in different traffic conditions and region types were revealed, and can provide useful proposals to regional planning, traffic planning and smart distribution of people in China.     

Demographic consequences of chronic anthropogenic disturbance on three populations of the endangered globose cactus Coryphantha werdermannii

Cacti are thought to be highly vulnerable to chronic anthropogenic disturbance (CAD). To assess its effects, we modeled the dynamics of three populations of the endangered cactus Coryphantha werdermannii exposed to different intensities of disturbance. Because no seedlings germinated and survived in the less-disturbed site, we analyzed two different scenarios: If the same, average germination probability was used for all sites, the population growth rates (λ) decreased with disturbance, but λ remained unchanged if a very low germination probability was assigned to the less-disturbed site and the observed probabilities were used for the remaining populations. Retrospective analysis showed that different demographic processes affected λ as a result of increasing disturbance: The unsuccessful establishment of seedlings in the preserved site diminished λ. The damage caused by livestock to reproductive structures in the site with intermediate disturbance was responsible for a reduction in λ. In the most disturbed site, the reduced individual growth rates that seemingly resulted from land degradation caused a decrease in λ. No simple management strategy can be proposed because different threats require attention depending on disturbance intensity. CAD had both positive and negative effects on λ, conferring this species with a certain degree of tolerance.     

Assessment of Jovian synchrotron radiation with a bi-modal electron population

An explicit formula is developed to explore the mechanism of the synchrotron radiation by using a bi-modal loss-cone distribution function. The variation of the distribution function along the field line is modeled in detail and the evaluation of the total power in the synchrotron radiation is presented. The variance of synchrotron radiation with latitude depends on the electron anisotropy; for low anisotropy, synchrotron radiation increases with latitude and reaches a maximum at the particle mirror points; for high anisotropy, it decreases with latitude and maximizes at the equator. A bi-modal population is therefore suggested to explain the radiation intensity which peaks both at the equator and at high latitude.     

一类捕食者—被捕食者种群模型的定性分析

利用常微分方程的定性理论,研究了两个种群具有非线性密度制约的捕食-被捕食者系统:dxdt=b0x(b1+b2x-b3x2)-b4xy,dydt=-cy+(αx-βy)y,的平衡点的性质,并证明了该系统存在唯一极限环的一个充分必要条件。     

Change of Cultivated Land and Its Implications on Food Security in China

1 Introduction FAO defined food security not only in terms of access to and availability of food, but also in terms of resources distribution to produce food and the purchasing power on food where it is not produced (Shi et al., 1996; Ning, 2004). Obviously, to guarantee everyone adequate food is the primary aim and most important content of food security (Xie et al., 1999). Thus, to increase food supply is a precondition for food security by domestic food production and international food t…     

On the effects of triangulated terrain resolution on distributed hydrologic model response

Distributed hydrologic models based on triangulated irregular networks (TIN) provide a means for computational efficiency in small to large‐scale watershed modelling through an adaptive, multiple resolution representation of complex basin topography. Despite previous research with TIN‐based hydrology models, the effect of triangulated terrain resolution on basin hydrologic response has received surprisingly little attention. Evaluating the impact of adaptive gridding on hydrologic response is important for determining the level of detail required in a terrain model. In this study, we address the spatial sensitivity of the TIN‐based Real‐time Integrated Basin Simulator (tRIBS) in order to assess the variability in the basin‐averaged and distributed hydrologic response (water balance, runoff mechanisms, surface saturation, groundwater dynamics) with respect to changes in topographic resolution. Prior to hydrologic simulations, we describe the generation of TIN models that effectively capture topographic and hydrographic variability from grid digital elevation models. In addition, we discuss the sampling methods and performance metrics utilized in the spatial aggregation of triangulated terrain models. For a 64 km² catchment in northeastern Oklahoma, we conduct a multiple resolution validation experiment by utilizing the tRIBS model over a wide range of spatial aggregation levels. Hydrologic performance is assessed as a function of the terrain resolution, with the variability in basin response attributed to variations in the coupled surface–subsurface dynamics. In particular, resolving the near‐stream, variable source area is found to be a key determinant of model behaviour as it controls the dynamic saturation pattern and its effect on rainfall partitioning. A relationship between the hydrologic sensitivity to resolution and the spatial aggregation of terrain attributes is presented as an effective means for selecting the model resolution. Finally, the study highlights the important effects of terrain resolution on distributed hydrologic model response and provides insight into the multiple resolution calibration and validation of TIN‐based hydrology models. Copyright © 2005 John Wiley & Sons, Ltd.     

土壤科学与环境保护

地球生物圈的重要组成部分——土壤，是对人类生计和生活都至关重要的动态生态系统。人类文明的崛起和衰败，无不与对土壤的合理利用和管理失当有关。据全球土壤分布地理及气候情况，适合农作物生长的土地并不多，然而全球人口的增长下世纪有可能达到１００亿。下个世纪，整个人类所面临的最大挑战将是如何在最贫困的国家中对付饥饿的幽灵、制止环境恶化以及人口的高速增长。本文力求阐明解决全球粮食需求、土壤对污水的处理和防止环境进一步恶化的方法。只有多学科的共同努力才能达到预期的目的。     

Population Parameters, Life Cycle, and Feeding of Mysidium columbiae (Zimmer) in the Waters Surrounding a Belizian Mangrove Cay

Abstract. The ecology of tropical Mysidacea is poorly known. Mysidium columbiae (Z immer ), because of its ubiquitous distribution in the tropical western Atlantic and the information available on its aggregative behavior, is an ideal subject of study to reconcile aspects of this problem. Information and data were obtained on abundance, population size, shoal/school structure, fecundity, development, and feeding of a M. columbiae population inhabiting waters surrounding Twin Cays, a mangrove archipelago in Belize. Although reproduction was continuous and proportions of life stages within shoals remained relatively constant throughout the year, population size decreased by an order of magnitude from summer to winter. Embryonic development averaged 4.7 days, with postlarvae being released near the surface before dawn. Aquarium experiments suggested that olfaction may be more sensitive than vision, although both senses were used to locate food. This species is a detritivore, but gut contents suggested that it may also be a predator.