Gravity Parameter Estimation

The question of whether ordinary least-squares (OLS) regression provides unbiased estimates for parameters of the gravity model is investigated. Holding attractiveness constant and looking only at the location of destinations, OLS is shown to give unbiased estimates if underlying behavior conforms to the gravity hypothesis. Johnston's conjectures on this are examined and found to explain only partially observed variations in distance exponents. Allowing attractiveness to vary, spatial autocorrelation in attractiveness is shown to lead to bias in OLS estimation due to misspecification, even where behavior conforms to the gravity hypothesis. Deterministic and stochastic illustrations are provided.     

A conceptual framework for analysing migration behaviour in the developed world

This paper explicates a theoretical scheme with which to orientate research aimed at explaining various facets of migration behavior. Both aggregate and individual level approaches are subsumed within the scheme, with the so-called behavioral perspective representing an attempt to probe inside the black box that exists between a set of observed variables and overt migration. 4 major links are postulated, relating 1) observed variables to observed behavior, 2) observed or objective variables to their subjective counterparts, 3) subjective variables to an overall utility value, and 4) the overall utility value to observed behavior. Suggestions for future research include 1) recognizing the limits of single-equation regression models, 2) recognizing that results from the transformation of objective variables into their subjective counterparts are likely to vary according to methodology, 3) considering powerful methodologies such as information integration theory and conjoint analysis, and 4) appropriately modifying the relationship between the overall utility value, or preference, and overt behavior to incorporate a variety of individual and institutional level constraints.     

An Assessment of the Space-Time Differential Model for Aggregate Trip Behavior to Planned Suburban Shopping Centers

Aggregate trip behavior to planned suburban shopping centers is studied in terms of changes in trip distance and shopping time within a framework of trip frequency, center scale, and consumer mobility. Such changes are expressed by a second-order differential equation. The assumed shopping strategy is that consumers accelerate the shopping trip cycle by minimizing trip distances. This can be solved to provide theoretical norms to assess against an exploratory data set compiled from 2,810 surveys undertaken in 1980/82 and 1988/89 over a range of centers. The analysis shows a significant relationship between the gravity coefficient and trip frequency. The samples are tested for periodicity using Fourier analysis. The results show that “small” centers are more likely to exhibit periodic behavior. “Large” centers do not follow this hypothesis. Both the gravity coefficient and trip frequency are shown to be quadratic functions of center size. The nonlinearity may be introduced by the agglomeration of shopping opportunities at larger centers. A critical value for “small-” and “large-”center behavior is determined from the minimum points of these distributions. A second equation from classical diffusion analysis is tested for “large” center behavior, where consumers accelerate spatial choice through a time minimization strategy. The results suggest that this strategy occurs at the midrange specialty center during the afternoon of the pre-Christmas rush rather than at large regional centers. The empirical characteristics of the three types of trip behavior are summarized.     

Toward Conceptualizing Trip-Chaining Behavior: A Review

This paper critically reviews the existing literature on multiple-trip journeys, and clarifies the need for an improved conceptualization and modeling strategy. It also suggests different ways that trip chaining can be treated and a theory constructed. Exploratory studies, from the 1960s and 1970s, are briefly surveyed (Section I). While they developed the existence and complexity of travel patterns, they lacked any comprehensive theoretical framework. However, they were useful in that they supported the conceptual framework of various kinds of stochastic processes used by transportation scientists to replicate trip-chaining behavior (Section II). Scientists subsequently improved their conceptualization of the issue by grounding individual behavior on the principle of utility maximization. In this latter area the economists have emphasized theoretical concerns while transportation researchers have emphasized operationality (Section III).     

Extremal Approaches to Estimating Spatial Interaction

Two recent theoretical approaches to the gravity model of spatial interaction are examined with emphasis on the dissimilar physical and statistical theories from which they were respectively derived. Formal relationships between the two methods are demonstrated. The two approaches jointly indicate a general method of generating new hypotheses of gravity flows. This method is discussed and evaluated, and some questions of theory comparability are explored. Comments on some of the computational features of each of the two models conclude the paper.     

A Generalization of the Utility Theory Approach To the Problem of Spatial Interaction

The derivation of the gravity model from utility theory is reformulated and generalized in order to show (1) how both the number of trips to individual destinations and the total travel budget may be determined simultaneously, and (2) how the effect of both distance and destination quality on trip distribution and total budget may be analyzed. Results are compared with the revealed space preference approach and are found to be superior in dealing theoretically with trip frequency and the effects of spatial context. For empirical applications, however, the revealed preference approach is advantageous.     

Gravity wave saturation and eddy diffusion in the middle atmosphere

A discussion is given of gravity wave saturation and its relation to eddy diffusion in the middle atmosphere. Attention is focused on the saturation process and some of its observable manifestations. It does not serve as a review of all related work. Although a theoretical point of view is taken, the emphasis is on which wave parameters need be measured to predict quantitatively the influence of gravity waves on eddy transport. The following considerations are stressed: the variation of spectra with observation time T; that eddy diffusivities are determined by velocity spectra; the anisotropic nature of diffusivity; a unified approach to saturation; an attempt to make eddy diffusivity more precise; the relationship between eddy diffusivity and wave dissipation.The subjects of ‘wave drag’ (momentum flux deposition) and heat flux need only be treated briefly, because they are related to eddy diffusivity in simple ways. Consideration is also given to two different theoretical mechanisms of wave saturation—wave induced convective instability and strong nonlinear wave interactions. The saturation theory is then used to predict a globally averaged height profile of vertical diffusivity in the middle atmosphere. This calculation shows that gravity waves are a major contributor to eddy diffusion from heights of 40–110 km, and that they are significant down to 20 km. A more detailed calculation of wave induced eddy diffusion, including latitudinal and seasonal variations, can be made if wave velocity spectra become available. The paper closes with recommendations for future research.     

Gravity wave heating: a simple expression for the enhanced energy flux

A simple expression for the heat flux by irregular motions, such as gravity waves, turbulence and other convective systems enhancing transport, can easily be obtained if a hypothesis similar to Fick's diffusion law is made i.e. “The energy flux is proportional to the gradient of the energy per unit volume”. The validity of the expression for the energy deposition derived from this hypothesis is tested by comparing with values obtained by means of classical expressions. Data on the 557.7 nm airglow line measured at Sierra Nevada and analyzed in terms of gravity waves as described in our previous work (Battaner and Molina, 1980) were used for this comparison. We consider that this simplified equation can profitably be used, when detailed information on gravity waves or turbulence are not available.     

ANALYZING THE COST OF DEBT FOR SMALL BUSINESS

The available empirical evidence provides mixed views of small businesses' relative bankruptcy risk. The difference between Churchill and Lewis' findings and SBA's and Kirchhoffs' may well lie in the difference in definition of firm “size” used. Risk is not evenly spread; the smallest businesses seem to be less risky than the intermediate size businesses. Yet, Churchill and Lewis' actual loss evidence suggests that small business risk is only marginally greater than for large businesses, the loss rate is still equivalent to less than one half of one percent. The assumptions that lenders will adjust the amount of debt they allow small business clients rather than the interest rate is not rejected by this evidence. In fact, the much higher profitability of the small business department reported by Churchill and Lewis suggests that the bank's loan interest rates are more than high enough to cover loss risk and fixed costs, and borrowers provide profitable deposits. Thus, the logic of my utility theory hypothesis provides a reasonable explanation for the relatively higher debt levels of small firms compared to large firms. But, then the Kirchhoffs' findings cast some doubt on whether small firms actually have higher debt levels. None of these findings justify the 2.75 percent interest rate spread allowed by SBA.     

Dimensional Analysis: Some Applications In Human Geography

Dimensional analysis is introduced, and applications of it to human geography are considered. Primary and secondary dimensions are selected; techniques of dimensional analysis are used to derive and check a functional relationship drawn from central place theory, to test the dimensional implications of a power function (the Pareto gravity model), to disaggregate a theoretical parameter (the exponential distance decay coefficient), and to simplify a complex system of variables in agricultural location theory to a system of dimensionless products. Difficulties inherent in the application of dimensional analysis to human geography are discussed.     

城市规划的基础理论研究

本文从哲学、方法论的角度对城市规划的基础理论问题进行了探讨,提出了城市规划理论的两个来源:实践与假说。对规划理论的作用进行了评价,设想了规划的理论体系。     

A Theory‐Based Cellular Automata for the Simulation of Land‐Use Change. 基于理论细胞自动机的土地利用变化模拟

This study proposes a theory‐based cellular automata (CA) in which CA rules are constructed on the basis of a theory of urban land‐use change and other local conditions. Rent gap theory that describes urban redevelopment and exogenous conditions that reflect urban development are embedded into a CA to simulate changes of land use. The theoretical framework provides a strong conceptual background for the CA simulation. A case study demonstrates the flexibility of the integrated framework for simulating land‐use changes in complex settings. This research aims to help decision‐makers formulate appropriate development plans.     

犯罪地理学的理论研究

目前,国内外学术界还没有建立起真正意义上的犯罪地理学,因此,犯罪地理学的理论研究就显得特别重要。为此,本文系统地探讨了犯罪地理学的理论体系,认为犯罪地理学的理论体系含有:①地理环境决定论;②环境论(月相说、星相说、地域说、犯罪地形说、折衷主义学派环境论);③犯罪时日论;④芝加哥学派的犯罪同心圆论;⑤犯罪区位论。通过犯罪地理学理论体系的研究,希望有益于犯罪地理学的创建和发展。     

On Scientific Hypotheses and Authentic Knowledge in Modern Discoveries of General Regularities in Physical Geography

The methodological aspects of the relationship between scientific hypothesis and authentic theory are examined with particular reference to the discoveries of regularities in the field of physical geography. A hypothesis is defined as a proposition whose basic content may be refuted as a result of further research; the basic content of authentic theory is beyond dispute, but may be further altered and refined. Instead of a traditional opposition of hypothesis to theory, the author recommends a broader approach treating both the formulation of a scientific hypothesis and the creation of a theory as discoveries of a theoretical character. According to this view, discoveries may be in the realm of hypothetical knowledge or in the area of authentic knowledge, depending on the weight of evidence. The Wegener hypothesis of continental drift is viewed as an example of a discovery in the realm of hypothetical knowledge; global regularities of heat-moisture relationships deriving from solar radiation are regarded as falling in the area of authentic knowledge. In general, hypothetic knowledge tends to involve the earth's interior forces, which are still relatively unknown, and authentic knowledge the better-known forces stemming from the sun. Some discoveries, such as the problem of geographical zonality and the discovery of bipolarity in the morphometry of the earth's macrorelief, contain elements of both authentic and hypothetical knowledge.     

Comprehensive meteorological modelling of the middle atmosphere: a tutorial review

This paper reviews the current state of comprehensive, three-dimensional, time-dependent modelling of the circulation in the middle and upper atmosphere from a meteorologist's perspective. The paper begins with a consideration of the various components of a comprehensive model (or general circulation model, GCM), including treatments of processes that can be explicitly resolved and those that occur on scales too small to resolve (and that must be parameterized). The typical performance of GCMs in simulating the tropospheric climate is discussed. Then some important background on current ideas concerning the general circulation of the stratosphere and mesosphere is presented. In particular, the transformed-Eulerian mean flow formalism, the role of vertically-propagating internal gravity waves in driving the large-scale circulation, and the notion of a stratospheric surf zone are all briefly reviewed. Using this background as a guide, some middle atmospheric GCM results are discussed, with a focus on simulations made recently with the GFDL ‘SKYHI’ troposphere-stratosphere-mesosphere GCM. The presentation attempts to emphasize the interaction between theory and comprehensive modelling. Many theoretical notions cannot be confirmed in detail from observations of the real atmosphere due to the various limitations in the observational methods, but can be very completely examined in GCMs in which every atmospheric variable is known perfectly (within the limits of the numerical methods). It will be shown that our understanding of both the role of gravity waves in the general circulation and the nature of the stratospheric surf zone has benefited from analysis of GCM results.From the point of view of the upper atmosphere, one of the most interesting aspects of GCMs is their ability to generate a self-consistent field of upward-propagating gravity waves. This paper concludes with a discussion of the gravity wave field in the middle atmosphere of GCMs. Comparisons of the explicitly-resolved gravity wave field in the SKYHI model with observations are quite encouraging, and it seems that the model is capable of producing a gravity wave field with many realistic features. However, the simulated horizontal spectrum of the eddy momentum fluxes associated with the waves is quite shallow, suggesting that much of the spectrum that is important for maintaining the mean circulation is not explicitly resolvable in current GCMs. A brief discussion of current efforts at parameterizing the mean flow effects of the unresolvable gravity waves is presented.     

Social agency and the dynamics of prehistoric technology

Technology is not only the material means of making artifacts, but a dynamic cultural phenomenon embedded in social action, worldviews, and social reproduction. This paper explores the theoretical foundations for an anthropology of technology that is compatible with this definition. Because of its focus on social agency, practice theory provides an appropriate starting point for a social theory of technology. In addition, three other themes require explicit attention: scale, context, and the materiality of technology. Four case studies demonstrate how archaeologists are beginning to take technology beyond its material dimensions, and additional questions are proposed stemming from the theoretical issues raised in the paper. The purpose of this essay is to synthesize a diverse set of emerging ideas and approaches to understand better dynamic community-level social processes of prehistoric material culture production.     

ELASTICITIES OF CONSTRAINED GRAVITY MODELS*

ABSTRACT Doubly constrained gravity models require a balancing procedure to make estimated origin and destination totals consistent. We show through a series of examples that not just the magnitudes but even the signs of derivatives and elasticities of gravity model flows depend on the specific balancing procedure used. Hence, if such elasticities are regarded as meaningful, then the balancing of origin and destination totals must be regarded as an integral part of the gravity theory itself.     

联系与竞合：粤港澳大湾区城市群旅游共生空间若干问题研究

首次从旅游领域将共生理论分析框架应用到城市间空间相互作用中,对城市群旅游共生进行理论分析。通过引力模型、欧氏距离模型和共生系统分类法,探讨粤港澳大湾区城市群旅游共生空间的若干问题。研究表明：城市群旅游共生组织模式基本处于由间歇共生向连续共生的正向演化阶段,空间呈现“2+3+4+2”城市群旅游共生层级体系,形成了三大旅游共生城市组团。城市群旅游共生行为模式大都处于由竞争共生向互惠共生的正向演化阶段,港澳广莞和佛惠中分别为主要互补与竞争节点,出现正向、稳定、逆向、往复、随机无序等五种演化路径分异。城市群旅游共生系统表现为初级旅游共生关系单一且稳定,中级旅游共生关系混沌且随机,高级旅游共生关系分异且稳定的规律。     

Social Movements,Political Elites and Political Opportunity Structures: The Case of the Woman Suffrage Movement from 1890-1920

Many contemporary theories of party leadership derive their concepts from organization theory and economic theories of rational choice. They stress the institutional contexts that shape leadership possibilities and the relationship between members (principals) and leaders (agents) in shaping leadership decisions. Both the macro (institutional context) and micro (principal-agent) theories assume that the main role of party leaders is to marshal majority support for legislation on which the party takes a position. Focussing on party position legislation, however, provides only a partial view of party leadership. This article expands this perspective by considering the Simpson-Mazzoli immigration reform bill, in which party leaders avoided taking a clear policy stand and pursued other interests instead. In broadening the assumptions inherent in organization theory to include behavior beyond taking party policy stands, we uncover leadership roles that are missed by those who adopt the policy-centered approach. Applying other organization theory concepts, we broaden principal-agent theories by explaining divergent leadership roles in the consideration of non-party position legislation as behavior that is typical for legislative leadership. We conclude that the nature of non-party position legislation provides party leaders a greater latitude to diverge from their expected party leadership roles and to behave according to their different strategic situations, district and state interests, philosophies, and personalities.