A path that buys time to decide where to go

This paper considers the problem of planning a path in a circumstance where its origin is given, but its destination is not specified and is to be selected from among a set of candidate destinations during a trip. A situation like this may be experienced by a group of people who have different preferred destinations, as well as by an individual who is simply indecisive about where to go. To resolve such an uncertainty, one may stay at the origin until he decides on a destination, or choose to proceed on some path that does not overly deviate from a shortest path, whichever destination is eventually chosen, and make a decision on the way. The latter action is sensible when the risk of traveling longer is outweighed by the benefit of buying more time for a better destination decision. The problem of finding such a time-buying path is formulated and a simple algorithm is developed for its solution. Some extensions and applications are also discussed.     

The Minkowski approach for choosing the distance metric in geographically weighted regression

In this study, the geographically weighted regression (GWR) model is adapted to benefit from a broad range of distance metrics, where it is demonstrated that a well-chosen distance metric can improve model performance. How to choose or define such a distance metric is key, and in this respect, a ‘Minkowski approach’ is proposed that enables the selection of an optimum distance metric for a given GWR model. This approach is evaluated within a simulation experiment consisting of three scenarios. The results are twofold: (1) a well-chosen distance metric can significantly improve the predictive accuracy of a GWR model; and (2) the approach allows a good approximation of the underlying ‘optimal distance metric’, which is considered useful when the ‘true’ distance metric is unknown.     

Sudden Local Conductivity Changes in the Ionosphere

Summary. An attempt is made to describe the transient magnetic change caused by a sudden local change of conductivity in the ionosphere. In a rough illustrative model, electric current is taken to be flowing uniformly in a thin plane rigid sheet of uniform isotropic integrated conductivity, I/ϱO e.m.u. A particular type of perturbing current system is defined, and the type of conductivity anomaly which could produce it is derived. It is shown that the problem is equivalent to that of the free decay of the perturbing current system. For a very small change of conductivity, the current system is found to spread radially at a uniform rate, while decaying. The case of a large conductivity anomaly is analysed by a numerical method. It is concluded that effects at a distance would be similar to those produced by a very small change, and that near the anomaly there would be as well, a local decaying current vortex system. It is found in particular, that at a large distance L cm, the magnetic change would commence immediately and reach an extremum after time of order L × 10⁻⁶ s.     

Shallow earthquakes in a viscoelastic shear zone with depth-dependent friction and rheology

Summary. Most crustal earthquakes of the world are observed to occur within a seismogenic layer which extends from the Earth's surface to a depth of a few tens of kilometres at most. A model is proposed in which the shear zone along a transcurrent plate margin is represented as a viscoelastic medium with depth-dependent power-law rheology. A frictional resistance linearly increasing with depth is assumed on a vertical transcurrent fault within the shear zone. Such a model is able to reproduce a continuous transition from the brittle behaviour of the upper crust to the ductile behaviour at depth. Assuming that the shear zone is subjected to a constant strain rate from the opposite motions of the two adjacent plates, it is found that there exists a maximum depth H below which tectonic stress can never reach the frictional threshold: this may be identified as the maximum depth of earthquake nucleation. The value of H is consistent with observations for plausible values of the model parameters. The stress evolution in the shear zone is calculated in the linear approximation of the constitutive equation. A change in rigidity with depth, which is also introduced in the model, may reproduce the high vertical gradient of shear stress, which has been measured across the San Andreas fault, and the fact that most earthquakes are nucleated at some depth in the seismogenic layer. A crack which drops the ambient stress to the dynamic frictional level is then introduced in the model. To this aim, a crack solution is employed without a stress singularity at its edges, which is compatible with a frictional stress threshold criterion for fracture. A constraint on the vertical friction gradient is obtained if such cracks are assumed to be entirely confined within the seismogenic layer.     

Cloudburst floods in mountains: State of knowledge,occurrence, factors of formation

A detailed analysis is made of the current ideas concerning floods of a special type. We examine short-lasting torrential flash floods, one of the most widespread and hazardous natural phenomena in the world characterized by a high rate of development, and by a short duration. It is established that such floods are in a primitive stage of study, which is testified by the fact that there is no general consensus as to what should be treated as a flash flood. It is pointed out that a special term designating them is also absent in many countries. It is determined that the key formation conditions for flash floods include intense short-lasting cloudbursts, the occurrence of a river basin in mountainous regions and a small drainage area; on this basis, it is suggested that they be termed flash floods. It is shown that such floods are of the most widespread occurrence in the northern hemisphere in regions with a temperate and subtropical climate. We suggest the scheme of natural factors for formation of flash floods and their differences from debris flows and floods of other types. It is determined that the main problems of investigating the formation mechanisms and forecasting the aforementioned floods are associated with the small spatiotemporal scale of these phenomena.     

GEOGRAPHIC NOTEBOOK: CHANGE AND GEOGRAPHY

Life is an evolution. We concentrate a period of this evolution in a stable view which we call a form, and, when the change has become considerable enough to overcome the fortunate inertia of our perception, we say that the body has changed its form. But in reality the body is changing form at every moment; or rather there is no form, since form is immobile and reality is movement. What is real is the continual change of form: form is only a snapshot view of transition.     

The shifting territory of government: some insights from the Rural White Paper

Summary In this paper it is proposed that the territory of governance is currently being reconfigured by the state. The state is pulling back from a universalist, welfare role, which entailed comprehensive governance of the whole national territory. Now a much more selective form of government is coming into being, concerned with 'community', 'diversity' and 'locality'. This is not, however, simply a belated recognition by the state that these are ever more important features of socio-spatial life: rather, it is part of the reconfiguration of the territory of government as the state invokes these characteristics in order to modify its ways of governing. Using Foucault's concept of governmentality–that is the means used by the state to 'problematise' life within its territorial borders and then act on the basis of these problematisations—the recent case of the Rural White Paper is examined. It is proposed that this is a very clear example of a governmental retreat from a comprehensive role in the governance of rural areas and shows how the state now seeks to govern 'through communities'.     

Synfolding magnetization: detection, testing and geological applications

A correct method for determining the direction of a synfolding remanence is described, and a new test, which in a number of cases can discriminate between a true synfolding remanence and a remanence that is the sum of pre- and post-folding components, is suggested. It is shown that it is possible to reveal the folding evolution of a local object under an assumption that the acquisition of the synfolding remanence was synchronous over this object.     

Mobilocality

Based on the ethnographic research and in-depth interviews in Flushing, Queens, New York City, this paper proposes the concept of mobilocality. Mobilocality provides a conceptual framework to examine the urban ethnic communities through the lens of mobility from a multi-scalar perspective. Mobilocality is formed by the paradox of transnational mobility and local immobility that are simultaneously embedded in everyday life of (im)migrants. It is through mobilocality where individual is ethnic, ethnic is transnational, transnational is urban. This article also suggests a placed and contextual understanding of mobility by illustrating the interrelationships among the four spatialities: mobility, place, scale and distance. The making of mobilocality is an outcome of the dialectal process among these spatialities, which involves not only spatial-temporal dimensions, but also social and cultural context. Transnationalism is far from a celebration of cosmopolitanism and diversity. Rather, it is a divergent process that generates heterogeneity and boundaries, a product of time-space distortion instead of time-space compression.     

地区发展水平衡量指标体系设计及实例分析

选定地区发展水平衡量指标，测度区域社会，经济，文化发展水平或发育程度是一项有重要的工作，本文试图为量度我国西部地区发展水平提供一套昼完整的指标体系，并对一个具体实例进行衡量和计算，由此说明地区的区内发展程度的差异，划分区域发展的不同类型。     

喀斯特洞穴旅游开发

喀斯特洞穴在我国分布广泛，数量多，是一种区域性的旅游资源，通过大量的案例分析，本文阐述喀斯特洞穴资源和旅游生命周期特点，划分出孤立的，组合的，镶嵌的，介入机会的４种类型，探讨喀斯特洞穴的旅游开发问题。     

Water resources utilization and eco-environmental safety in Northwest China

Northwest China includes Xinjiang Ugyur Autonomous Region, Qinghai Province, Gansu Province, Ningxia Hui Autonomous Region and Shaanxi Province, covering 308×104 km2. It is located in the warm-temperate zone and the climate is arid or semi-arid. Precipitation is very scarce but evaporation is extremely high. The climate is dry, the water resources are deficient, the eco-environment is fragile, and the distribution of water resources is uneven. In this region, precipitation is the only input, and evaporation is the only output in the inland rivers, and precipitation, surface water and groundwater change with each other for many times, which benefits the storage and utilization of water resources. The average precipitation in this region is 232 mm, the total precipitation amount is 7003×108 m3/a, the surface water resources are 1891×108 m3/a, the total natural groundwater resources are 1150×108 m3/a, the total available water resources are 438×108 m3/a, and the total water resources are 1996×108 m3/a and per capita water resources are 2278 m3/a. The water resources of the whole area are 5.94×104 m3/(a.km2), being only one-fifth of the mean value in China. Now, the available water resources are 876×108 m3/a, among which groundwater is proximate 130×108 m3/a.     

关于主题旅游协作网络建设的探讨——以"霞客行"旅游网络为例

旅游协作是旅游系统本身的要素关联,是其客观属性和发展的必然。主题旅游协作是以某一个主题为"红线",将相关旅游要素组织起来形成一个旅游协作组织形式。目前关于旅游协作研究中很少涉及主题旅游协作。文中以"霞客行"旅游网络计划为例,讨论了名人故居旅游地开发中,重视物质性遗产开发,忽略非物质性品牌利用所导致的"大品牌,小产品"的问题,提出了利用虚实结合手法,通过主题品牌运作,构建综合性主题旅游协作网络的构想。旨在通过一个产品网络、一个市场网络、一个学术网络和一个虚拟网络的运作来充分发挥徐霞客品牌的纽带作用,以此推动相关主题旅游地协作单位之间的产品共享和市场共享,从而实现协作体系的效益最大化。     

黑河流域气象要素与全球性大气环流特征量的多尺度遥相关分析

黑河流域生态-水文过程集成研究是我国近年来干旱半干旱地区的研究热点,气候变化条件下流域生态-水文过程的响应机制是其中一个重要科学问题。基于1956-2015 年黑河流域气温、湿度、降水观测数据及多个大气环流特征量监测资料,采用小波分析方法研究了流域气象要素与大气环流特征量的周期性及遥相关。结果表明：（1）流域气温与大气环流特征量的遥相关关系最为明显,湿度、降水次之。（2）气温与Niño3.4 SSTA、SOI 的显著遥相关共同周期为12～16 a,与NAO、AO为9～11 a,与WP遥相关周期为5～9 a,与PDO为8～15 a。（3）湿度与NAO遥相关周期为4～5 a,与POL为3～6 a,与WP为9～15 a,与PNA为2～8 a。（4）降水与Niño3.4 SSTA遥相关周期为9～15 a,与NAO为2～4 a,与AO为3～7 a,与POL为11～19 a,与WP为9～14 a。（5）上述各遥相关周期的地域分布、显著时段与时滞特征各有差异。本文研究有助于加深流域气象要素对环流特征量响应机制的认识,为我国干旱半干旱地区内陆河流域严峻的水-生态问题的解决及水资源管理提供依据。     

极化还是均衡:重塑大国经济地理的战略选择——城市规模分布变化和影响因素的跨国分析

关于国家空间发展战略,经济学家主张要素向中国沿海发达地区自由流动,而城市和经济地理学家则认为应对不发达地区发展给予支持。本文以国家尺度的城市规模分布来测度经济地理格局和城市化空间结构,综合运用截面和面板双重估计方法,探索了国家经济地理格局与国家规模的关系。结论显示,在控制了其他因素后,表征国家规模的人口规模和国土面积与国家经济地理的均衡分布呈现显著正相关,即大国的经济地理倾向于多中心均衡布局。机制在于,经济中心的辐射半径不是无限的,地理或者更准确地说是距离对于生产力和城市化布局具有重要作用。此外,随着经济水平的提高,国家经济地理格局呈现先极化后均衡的演化趋势;城市化率和非农产业比重的提高以及稳定的政治环境同样也会促进国家经济地理格局向均衡方向发展。再考虑到国家安全、社会稳定的政治诉求和中国地大物博的既有现实,本文政策启示是,大国的经济地理和城市化格局应该走适度均衡发展之路,国家采取空间干预政策促进中国不发达地区的发展有其合理性和必要性。     

Polarization and amplitude attributes of reflected plane and spherical waves

The characteristics of a reflected spherical wave at a free surface are investigated by numerical methods; in particular, the polarization angles and amplitude coefficients of a reflected spherical wave are studied. The classical case of the reflection of a plane P wave from a free surface is revisited in order to establish our terminology, and the classical results are recast in a way which is more suited for the study undertaken. The polarization angle of a plane P wave, for a given angle of incidence, is shown to be 90° minus twice the angle of reflection of the reflected S wave. For a Poisson's ratio less than 1/3, there is a non-normal incident angle for which both amplification coefficients are 2 precisely; for this incident angle the direction of the particle motion at the free surface is also the direction of the incident wave. For a wave emanating from a spherical source, the polarization angle, for all angles of incidence, is always less than, or equal to, the polarization angle of a plane P wave. The vector amplification coefficient of a spherical wave, for all angles of incidence, is always greater than the vector amplification coefficient of a plane P wave. As expected, the results for a spherical wave approach the results for a plane P wave in the far field. Furthermore, there was a good agreement between the theoretical modelling and the numerical modelling using the dynamic finite element method (DFEM).     

A method for assessing regional debris flow risk: an application in Zhaotong of Yunnan province (SW China)

Based on the definitions of the United Nations, the assessment of risk involves the evaluation of both hazard and vulnerability. This forms the basis of a generalized assessment model of debris flow risk. Hazard is a measure of the threatening degree of an extreme event and is expressed theoretically as a function of event magnitude and frequency of occurrence. Mathematically, it is the definite integral area under the magnitude–frequency curve. Based on the need for a model applicable in regions that lack data, a new method that incorporates theoretical concepts with empirical analysis is presented to calculate the regional hazardousness of debris flows. Debris flow hazard can be estimated from gully density, mean annual rainfall and percentage of cultivated land on steep slope. Vulnerability is defined as the potential total maximum losses due to a potential damaging phenomenon for a specified area and during a reference period. On a regional scale, it is dependent on the fixed assets, gross domestic product, land resources and population density, as well as age, education and wealth of the inhabitants. A nonlinear, power-function model to compute the vulnerability degree is presented. An application of the proposed method to Zhaotong prefecture of Yunnan province, SW China, provides high accuracy and reasonable risk estimates. The highest risk of debris flow is in Zhaotong county with a value of 0.48; the lowest risk of debris flow is in Yanjin county with a value of 0.16. The other counties have debris flow risks ranging from 0.22 to 0.46. This provides an approach for assessing the regional debris flow risk and a basis for the formulation of a regional risk management policy in Zhaotong prefecture.     

基于网格计算的城市地理学研究方法探讨

综合分析了城市地理学研究的几种基本方法,并重点探讨了G IS技术在城市地理学研究的重要应用。指出多源数据的获取、数据共享、模型方法的互操是目前城市地理学研究面临的重要问题,建议将网格计算这一新的分布式计算技术应用到城市地理学的研究中,并给出一个基本的城市地理学网格计算体系结构,讨论了实现这个计算体系的几个关键问题,认为采用W eb Service标准建立城市地理学研究的网格计算体系是目前可行的方法。     

人口扩散与空间相互作用的联系

本文以人口为基本形象,发现了空间相互作用与地理扩散的关系,导出了最大熵原理分析未得出的一些新的结论。     

Modelling quartz cementation of quartzose sandstones

Cementation of quartzose sandstones is modelled assuming that the main source of silica is quartz dissolved at stylolites. The cementation process is shown to operate in one of two different regimes depending on the Damköhler number for diffusion. The regime, where diffusion of silica from the stylolites is a faster process than precipitation, is characterized by a nearly constant supersaturation between the stylolites. This regime, which spans the depth interval of quartz cementation for close stylolites, allows for approximate analytical expressions for the porosity evolution as a function of time and temperature. An expression is derived for the temperature where half the initial porosity is lost during constant burial along a constant thermal gradient. This expression is used to study the sensitivity of all parameters which enter the cementation process. The cementation process is shown to be particularly sensitive to the activation energy for quartz dissolution. The expression for the porosity decrease under constant burial is generalized to any piecewise linear burial and temperature history. The influence of the burial histories on the cementation process is then studied.