bluuebunny/crossref_metadata_2025 huggingface dataset:
Homoepitaxial growth and electrical characterization of iron-doped semi-insulating 4H-SiC epilayer
Authors: Song Ho Keun , Kwon Sun Young , Seo Han Seok , Moon Jeong Hyun , Yim Jeong Hyuk , Lee Jong Ho , Kim Hyeong Joon , Jeong Jae Kyeong
Published: October 2006

The authors attempted to grow a semi-insulating silicon carbide (SiC) epitaxial layer by in situ iron doping. The homoepitaxial growth of the iron-doped 4H-SiC layer was performed by metal-organic chemical vapor deposition using the organo-silicon precursor bis(trimethylsilylmethane) (C7H20Si2) and the metal-organic precursor t-butylferrocene (C14H17Fe). For the measurement of the resistivity of the iron-doped 4H-SiC epilayers, the authors used the on resistance of Schottky barrier diode. Based on the measurement of the on resistance, it is shown that the free carrier concentration was decreased with increasing partial pressure of t-butylferrocene. The resistivity of the iron-doped 4H-SiC epilayer was about 108Ωcm.
Merger of coherent structures in time-periodic viscous flows
Authors: Speetjens M. F. M. , Clercx H. J. H. , van Heijst G. J. F.
Published: October 2006

Inertia-induced changes in transport properties of an incompressible viscous time-periodic flow are studied in terms of the topological properties of volume-preserving maps. In the noninertial limit, the flow admits one constant of motion and thus relates to a so-called one-action map. However, the invariant surfaces corresponding to the constant of motion are topologically equivalent to spheres rather than the common case of tori. This has fundamental ramifications for the effect of inertia and leads to a new kind of response scenario: resonance-induced merger of coherent structures.
Isotope effects in the infrared spectra of OCS–He complexes and clusters
Authors: Abusara Z. , Borvayeh L. , Moazzen-Ahmadi N. , McKellar A. R. W.
Published: October 2006

Infrared spectra of the OCS–He van der Waals complex and of OCS–HeN clusters have been studied in the region of the OCS ν1 fundamental band using a tunable diode laser to probe a pulsed supersonic slit jet. For the complex, the spectrum of the normal isotope, O16C12S32–He4, has been considerably extended and the S34- and C13-substituted forms have been recorded for the first time. The data could be analyzed satisfactorily using a conventional asymmetric rotor Hamiltonian with sextic centrifugal distortion terms. For the clusters, the S34- and C13-substituted forms have been observed and assigned for N=2–7, including some transitions with higher J values than previously reported for the normal isotope, e.g., R(5). The observed vibrational shifts, relative to the free OCS molecule, were very similar to those of the normal isotope, and most of the difference could be explained by simple scaling. These results constitute a subtle and precise probe of intermolecular forces and dynamical effects in a system which is of current interest for cluster studies.
Mean sheared flow and parallel ion motion effects on zonal flow generation in ion-temperature-gradient mode turbulence
Authors: Anderson J. , Kishimoto Y.
Published: October 2006

The present work investigates the direct interaction of sheared mean flow with zonal flows (ZFs) and the effect of parallel ion motion on ZF generation in ion-temperature-gradient (ITG) background turbulence. An analytical model for the direct interaction of sheared mean flows with zonal flows is constructed. The model used for the toroidal ITG driven mode is based on the equations for ion continuity, ion temperature and parallel ion motion, whereas the ZF evolution is described by the vorticity equation. The behavior of the ZF growth rate and real frequency is examined for typical tokamak parameters. It is shown that in general the zonal flow growth rate is suppressed by the presence of a sheared mean flow. In addition, with parallel ion motion effects the ZFs become more oscillatory for increasing ηi(=Ln∕LTi) value.
Helicase mediated active DNA unwinding in a stochastic field
Authors: Das Tamal , Chakraborty Suman
Published: October 2006

The mechanism of unwinding of DNA by a class of motor proteins called helicase, in contact with a thermal bath, is theoretically investigated. The dynamic simulations, incorporating the considerations of externally applied unwinding forces as well as stochastically fluctuating Langevin interactions, are utilized to calculate the critical force required for the base pair opening, which comes out to be in close agreement with the experimentally obtained results. The simulation predictions effectively demonstrate how the thermal stochasticities can be overridden by directional openings, as an extended viewpoint of the classical Peyrard-Bishop [Phys. Rev. Lett. 62, 2755 (1989)] model.
Resonant tunneling diode made of organic semiconductor superlattice
Authors: Park Tae Jin , Lee Yong Kyun , Kwon Soon Kab , Kwon Jang Hyuk , Jang Jin
Published: October 2006

The authors studied the current-voltage characteristics of the organic superlattices of an ITO/1,3,5-tris-(3-methylphenylphenylamino) triphenylamine (m-MTDATA) (5nm)∕[m-MTDATAand4,7diphenyl-1,10-phenanthroline(Bphen)]4∕Bphen (5nm)∕LiF∕Al. The thickness of m-MTDATA was varied from 3to7nm with the fixed Bphen thickness at 3nm. The current-voltage characteristics of the organic superlattice show a peak and a valley between 3 and 8V when the thickness of m-MTDATA is 7nm, which is due to the resonant tunneling currents. It is found that there is no luminance by the resonant tunneling currents.
Positron emission tomographic map reconstruction using fuzzy-median filter
Authors: Mondal Partha Pratim
Published: October 2006

Positron emission tomography is widely used in medical physics for the reconstruction of the distribution of radionuclei molecules for analyzing regional physiological functions. The existing maximum a posteriori reconstruction methodologies produce artifacts such as oversmoothing and streaking. In this letter, the author proposes a potential function based on fuzzy-median filter for noise-free image reconstruction. The reconstruction methodology is therefore very useful for obtaining artifact-free reconstruction of biomedical specimens.
Quadraxial probe for high resolution near-field scanning rf/microwave microscopy
Authors: Karbassi A. , Paulson C. A. , Kozyrev A. B. , Banerjee M. , Wang Y. , van der Weide D. W.
Published: October 2006

The authors propose and demonstrate a miniaturized quadraxial probe that employs a differential feed technique for use in near-field rf/microwave transmission microscopy. Their quadraxial probe’s electric field measurements show higher electric field localization than a conventional coaxial (monopole) probe. The improved spatial resolution and more sensitive phase measurement of the quadraxial probe versus coaxial probe are further validated by a metal line scan experiment.
Grain surface temperature in noble gas discharges: Refined analytical model
Authors: Khrapak S. A. , Morfill G. E.
Published: October 2006

A model of grain surface temperature in a low-pressure weakly ionized complex plasma is refined by taking into account the effect of rare ion-neutral collisions in the vicinity of the grain. These collisions enhance plasma collection by the grain and can result in a considerable increase of the grain temperature. It is shown that the collision enhanced plasma collection model yields generally better agreement with the results of existing experiments. The effect of the temperature difference between the grain surface and the surrounding gas on the grain-grain interaction potential is also briefly discussed.
Effects of nanoparticle deposition on surface wettability influencing boiling heat transfer in nanofluids
Authors: Kim S. J. , Bang I. C. , Buongiorno J. , Hu L. W.
Published: October 2006

Buildup of a porous layer of nanoparticles on the heated surface occurs upon boiling of nanofluids containing alumina, zirconia, or silica nanoparticles. This layer significantly improves the surface wettability, as shown by a reduction of the static contact angle on the nanofluid-boiled surfaces compared with the pure-water-boiled surfaces. The contact angle reduction is attributed to changes in surface energy and surface morphology brought about by the presence of the nanoparticle layer. The high surface wettability can plausibly explain the boiling critical heat flux enhancement in nanofluids.
Optical properties of cubic Ti3N4, Zr3N4, and Hf3N4
Authors: Xu Ming , Wang Songyou , Yin Gang , Li Jing , Zheng Yuxiang , Chen Liangyao , Jia Yu
Published: October 2006

A systematic theoretical study is presented for the electronic, mechanical, and optical properties of cubic Ti3N4, Zr3N4, and Hf3N4 with the Th3P4 structure in the framework of density functional theory. The calculated band structures of Ti3N4, Zr3N4, and Hf3N4 show the indirect band gaps of 0.268, 0.909, and 1.00eV, respectively. Furthermore, the optical properties for all three materials were calculated and analyzed in detail. The calculated results are well consistent with available experimental data. Also, it is shown that all these materials have relatively large static dielectric constants at zero frequency, rendering them potential applications in microelectronic devices.
Polarized photoluminescence and absorption in A-plane InN films
Authors: Bhattacharyya Jayeeta , Ghosh Sandip , Gokhale M. R. , Arora B. M. , Lu Hai , Schaff W. J.
Published: October 2006

The authors report the observation of strong polarization anisotropy in the photoluminescence (PL) and the absorption spectra of [112¯0] oriented A-plane wurtzite InN films grown on R-plane (11¯02) sapphire substrates using molecular beam epitaxy. For A-plane films the c axis lies in the film plane. The PL signal collected along [112¯0] with electric vector E⊥c is more than three times larger than for E‖c. Both PL signals peak around 0.67eV at 10K. The absorption edge for E‖c is shifted to higher energy by 20meV relative to E⊥c. Optical polarization anisotropy in wurtzite nitrides originates from their valence band structure which can be significantly modified by strain in the film. The authors explain the observed polarization anisotropy by comparison with electronic band structure calculations that take into account anisotropic in-plane strain in the films. The results suggest that wurtzite InN has a narrow band gap close to 0.7eV at 10K.
Lethality mechanisms in Escherichia coli induced by intense sub-microsecond electrical pulses
Authors: Chalise P. R. , Perni S. , Shama G. , Novac B. M. , Smith I. R. , Kong M. G.
Published: October 2006

In this letter, the authors present the inactivation kinetics of cells of Escherichia coli and its mutants following treatment with high-intensity electrical pulses of 700 and 32ns durations. Their experimental results suggest that bacterial inactivation by 700ns pulses is consistent with a mechanism of reversible electroporation, whereas inactivation by 32ns pulses may occur as a result of damage to intracellular components. They believe that their results represent a first step towards elucidating the mechanism of lethality of submicrosecond pulses of different durations in prokaryotes.
The Interaction between Retailing and the Urban Centre Structure: A Theory of Spiral Movement
Authors: Agergård E. , Oisen P.A. , Aiipass J.
Published: October 2006

This paper deals with principles for the development of retailing and the urban centre structure. The main conclusion is that a projection of the trend of recent years could hardly be expected in spite of the fact that this is what most forecasts for retailing and centres are based upon. What is more likely to happen is a development in the form of a spiral movement which consequently makes it necessary to try other forecasting methods and other forms of mathematical models, different from the traditional ones. Such improved methods provide the basis also for an improved planning technique which in turn not only gives a split-second picture of the future situation, but also indicates how this situation is reached through extensive use of stage-planning.
The Urbanisation Effects of a Third London Airport
Authors: Cripps E.L. , Foot D.H.S.
Published: October 2006

This paper describes an application of a Lowry type model in a comparative study of the urbanisation effects, on an outer metropolitan sub-region, of locating the third London airport on two of the sites proposed by the Roskill Commission. The sites are at Cublington in Buckinghamshire and Thurleigh in Bedfordshire. No detailed attempt is made to explain the formal structure of the model. Attention is focussed instead on a description of the impact, in terms of activity change and inter-urban journeys, on the spatial structure of the Bedfordshire sub-region. The model is used first in a one-shot conditional prediction of the growth of the sub-region without an airport, and then including the airport in each of the proposed locations.
Structuring Urban Transportation Planning Decisions: Available Social Science Constructs
Authors: Hutchinson B. G.
Published: October 2006

A welfare-theory-based framework for the evaluation of urban transportation investments is described. An economic efficiency criterion is developed in terms of the community demand schedules for accessibility and for environmental quality. A procedure for modifying this efficiency criterion to reflect income distribution goals is presented. It is argued that the necessary empirical information for this evaluation framework must be derived from the application of some consistent theory of democratic group decisions. A number of models of the political process are then reviewed. Recent experience with several institutional frameworks for planning is discussed and some of the principles of the models are used to evaluate this experience. The contributions that available models of the political process might make to the extension of the welfare-based-evaluation framework are then explored. The elementary extensions presented in the paper provide a basis for studying the goal formulation and weighting processes in particular communities. Comparative studies in a number of urban communities should lead to the development of a meaningful institutional framework for urban transportation planning activities.
Derivation of the Negative Exponential Model by an Entropy Maximising Method
Authors: Bussière R. , Snickars F.
Published: October 2006

All the inhabitants of a city who participate in the choice of a place of residence are assumed to have a propensity to visit the urban centre. The distribution of residential locations is represented by a probability density surface whose horizontal plane projection is coextensive with that of the city. A spatially continuous system is thus defined in which it is shown that, under conditions of maximum entropy and subject to specific normalisation and cost constraints, the population is distributed in accordance with the negative exponential model of urban population densities.
Comparative Factorial Ecology: Some New Zealand Examples
Authors: Timms D W G
Published: October 2006

The use of factorial ecology in the analysis of residential differentiation is illustrated by data on the four main urban areas in New Zealand and by some historical data on Auckland. The article concludes by examining some of the implications of factorial ecology for urban theory.

Recent community analyses have indicated a renewed interest in one of the chief concerns of the early human ecologists: the effects and implications of residential differentiation and segregation. A notable aspect of the trend has been the application of factor-analytic methods to data generated for urban sub-communities(1). Analyses of census tract or enumeration district data in several North American, Scandinavian, and Australasian cities have shown that much of the detailed variation in the socioeconomic and demographic characteristics of the urban population may be expressed in terms of a small number of underlying factors relating to social rank, style of life or family type and, in ethnically heterogeneous populations, ethnic composition. Beshers (1962) suggests that the axes of differentiation are so clear that virtually any form of analysis will reveal their existence. Within the general pattern, however, it may be anticipated that local and regional differences in socio-cultural, economic, and political circumstances will result in variations in ecological structure. An attempt to delineate these variations is essential if the goal of developing a genuinely cross-cultural model of urban society is to be attained. It is in the pursuit of this end that the procedures of factorial ecology promise most. According to Sweetser (1965, p.219): “Modern factor analysis, using factor structure as a model for ecological structure, is the method par excellence for comparing cross-nationally (and intranationally) the ecological differentiation of residential areas in urban and metropolitan communities”. In the present example data from New Zealand is used to examine the usefulness of the factorial ecology approach for comparative studies at both the inter-city and the temporal levels.
Some Notes on Housing Market Models for Urban Planning
Authors: Kirwan R M , Martin D B
Published: October 2006

In this paper some of the problems of constructing a spatial model of the housing market from an economic standpoint are reviewed. These include the fragmentation of the market, the durability and heterogeneity of housing as an economic good, and the influence of preference variations. The authors go on to consider examples of two broad categories of model, the economic and the ‘social physics’, and conclude that for the purposes of urban planning there is merit in the deterministic approach of the economic model.
Search Behavior in an Intra-Urban Migration Context: A Spatial Perspective
Authors: Brown L A , Holmes J
Published: October 2006

This paper examines spatial search behavior related to intra-urban migration. Its approach is to draw upon related studies to derive expectations with regard to search patterns, and to test these through empirical analysis. This involves identifying and measuring distance, directional, and sectoral spatial biases, for which an algorithm is presented that employs a map transformation and standard ellipse analysis.
Space-Time Budgets and Activity Studies in Urban Geography and Planning
Authors: Anderson J
Published: October 2006

This paper attempts to provide a general perspective on the potentialities and limitations of research into individual activity patterns. The most common types of activity study and data-collecting device are briefly described, and problems of data collection and analysis are outlined. The main focus is on the value of ‘space-time budgets’ in household surveys, assessed with respect to two contrasting aims: (1) deriving ‘behavioural’ postulates on which geographic theories of spatial structure might be based, and (2) planning spatial structures to suit the behaviour patterns and aspirations of different types of individuals and households. Activities occur in a ‘space-time’ continuum’, and there are temporal regularities inherent in spatial patterns. It is argued that studying activity patterns in terms of ‘space-time locations’ can throw light on pressing socio-spatial problems.
Signed Digraphs and the Growing Demand for Energy
Authors: Roberts F S
Published: October 2006

Many problems of society, including those relating to energy use, air pollution and solid-waste disposal, seem amenable to formulation using the techniques of the rapidly growing field of graph theory, in particular, the notion of a signed digraph (directed graph). This paper outlines a methodology which exploits the signed digraph for handling problems of forecasting energy demand and the effect of new technologies and institutions on that demand, and for generating and analyzing policy alternatives for meeting environmental constraints on energy use. The forecasting and policy problems are translated into signed digraph problems, and in particular to problems of so-called pulse processes on signed digraphs. Research problems related to the development of the methodology are described.
Exploratory Calibration of a Retail Location Model Using Search by Golden Section
Authors: Batty M
Published: October 2006

This paper presents some experiments in calibrating a retail location model designed for the Kristiansand region in southern Norway. The form and behaviour of the model under extremes of its parameter values is first investigated, and then some calibration methods proposed by Hyman are tested. The need for a more general method is evident and a search procedure based on the Fibonacci numbers is outlined. A generalisation of this method, based on the golden section number, is derived and this method is used to explore the sensitivity of the model's goodness-of-fit to changes in parameter values. A fundamental result of these explorations shows that there is no unique fit for retail models with two parameters, and this result is likely to hold for other models of spatial interaction.
Quadrat Analysis of Urban Dispersion: 3. Bivariate Modelst
Authors: Rogers A , Martin J
Published: October 2006

This paper is a continuation of an earlier two-part essay on quadrat analysis. It extends the previous discussion by introducing bivariate models of spatial dispersion to analyze statistically the correlated spatial clustering of food stores and population in urban areas. The data used for empirical study are the spatial patterns of food stores and residential population in Ljubljana, Yugoslavia.
Volkswirtschaftliche Probleme Des Wohnungsbaus
Authors: Vogt K
Published: October 2006

Der Versuch die Probleme des Wohnungsbaus aus der volkswirtschaftlichen Perspektive auszuleuchten, macht zweierlich deutlich:

Die sozialpolitisch motivierte Wohnungsbauförderung bedarf offenbar einer Ergänzung des wirtschaftspolitischen Instrumentariums der Globalsteuerung, damit ein zufriedenstellender Zielerreichungsgrad erwartet werden kann. Der Weg weist in Richtung auf eine räumlich und sektoral stärkere Differenzierung der herkömmlichen Globalsteuerung wirtschaftlicher Abläufe.

Gleichzeitig muß die sozialpolitisch motivierte Wohnungsbauförderung künftig restriktiver wirkenden wirtschaftspolitischen Anforderungen gerecht werden, damit sie wirtschafts- und infrastrukturpolitisch tragbar wird und ihrerseits den Zielerreichungsgrad dieser Sektoren nicht unnötig herunternivelliert. Hier weist der Weg in Richtung auf einen verstärkten Ausbau der Individualförderung einerseits und einen mehr städtebaulich orientierten Wohnungsbau andererseits.
Toward a Technique for a More Exhaustive Evaluation of Urban Area Performance
Authors: Dickey J W , Broderick J P
Published: October 2006

One of the major aspects of urban area performance evaluation that has received little attention to date is that of the exhaustive identification of (exclusive) items to be considered in the evaluation. The object of this paper is to describe a technique useful for making such an identification and to suggest how the many factors that evolve can be culled and eventually utilized in conjuction with certain common evaluation procedures. The technique involves the cross categorization of a set of descriptive characteristics, obtained through a Thesaurus search, with a set of urban area elements, derived by expanding the Ekistics grid. The results obtained are the evaluation factors considered here.
Optimal Control Strategies for Air Quality Standards and Regulatory Policy
Authors: Gorr W L , Gustafson S -Å , Kortanek K O
Published: October 2006

The setting of air quality standards for classes of air pollution in a region is one approach to the protection of public health and welfare by defining limits on levels of pollution in the air.

We present methods to determine regional emission regulations that are (1) feasible in the sense that they lead to compliance with air quality standards and (2) optimal in the sense that the total economic impact due to implementation is minimized. Under goal (1) we set forth a procedure more sophisticated than heuristic procedures such as those guaranteeing compliance on a fixed rectangular set of grid receptor points in a region. We discuss various modifications responding to issues of regulatory policy, thereby obtaining a more accurate picture of the total impact of implementation of control strategies.

We also indicate how damage functions may be incorporated, where now the standard (or the set of multiple standards) is a variable to be determined, together with emission rate reductions, so as to minimize the joint sum of individual control costs for the region and the total of damage costs, while keeping pollutant emissions below standards (to be determined) at all point coordinates in the region.

In this way control strategies and emission standards may be derived jointly in a framework that automatically balances decrements of damage due to improved air quality with increased control costs associated with tighter standards. Furthermore the model determines the location of the maximum concentration intensities, which may not necessarily be on grid points, and hence indicates where to place sampling stations in order to guarantee compliance at all coordinates in the region over the prescribed period of time.
Quadrat Analysis of Urban Dispersion: 4. Spatial Sampling
Authors: Rogers A , Raquillet R
Published: October 2006

This paper is the concluding part of a four-part essay on quadrat analysis. It shows how quadrat analysis of spatial dispersion may be linked with Jessen's (1970) method of probability sampling with marginal constraints to produce more efficient spatial sampling schemes.
Space, Time and the Disruption of Behaviour in Cities
Authors: Cullen I G
Published: October 2006

Planning control of urban environments implies decisions which affect vast aggregates of population. Despite the extent of these consequences this paper presents a case for an initial approach to the problem of informing such decisions, which is disaggregated in the sense that it focuses on the behaviour of individuals. The fabric of a city which a planner helps to organize is no more than a context for behaviour, and the constraints and difficulties currently experienced by those operating in this context have been the objects of a research interest for some time. This paper summarizes this work and suggests possible extensions.
The Use of Forrester's Systems Dynamics Approach in Urban Modelling
Authors: Burdekin R , Marshall S A
Published: October 2006

In Urban Dynamics J. W. Forrester extended his system dynamics method to the problems of urban modelling. The article describes his concepts and model of the city and outlines some of their limitations. The results and implications of the model's use are also examined. The appendix describes and analyses some of the model's equations.
The Mathematics of Multiregional Demographic Growth
Authors: Rogers A
Published: October 2006

Mathematical demography traditionally has been concerned with the dynamics of the growth and structure of a population that is undisturbed by migration. In particular, attention has been directed at the relationships between a regional population's fertility and mortality schedules and its growth and age distribution. Recently, however, studies by the author and others have extended the mathematical theory of population growth in order to examine the relationships between a multiregional population's fertility, mortality, and mobility schedules and its growth and regional age distributions. This paper summarizes and reviews the major contributions of these studies.
Two Models for Multiregional Population Dynamics
Authors: Feeney G
Published: October 2006

A general linear demographic model is derived which subsumes a wide variety of previously proposed population models. The general model includes in particular the linear model of interregional population growth and distribution developed by Rogers and others. One feature of this model is criticized, the allocation of outmigrants from any region in constant proportions among possible destination regions. Insofar as persons migrate to economic opportunities, outmigrants will distribute themselves among regions in proportion to these opportunities. Insofar as the economy of a region services its population, opportunities will vary directly with population. This suggests the introduction of a new model which allows for the variable allocation of outmigrants from each region according to the distribution of population among possible destination regions. Such a model is proposed, and it turns out to be nonlinear. The linear and nonlinear models are compared by applying them to the analysis of migration between three regions of the United States during 1955–1960. In the course of developing the new model, a set of interregional migration statistics is defined which eliminates the imperfect duality between interregional in- and out-migration rates.
Accounts and Models for Spatial Demographic Analysis I: Aggregate Population
Authors: Rees P H , Wilson A G
Published: October 2006

This paper presents accounts and models which can be used for spatial demographic analysis. It is shown that in any time period there are sixteen different kinds of demographic flows for a two region system. These flows can be represented in an accounting table. Some of the minor flows, involving double or triple demographic events such as a birth followed by a migration, cannot be measured directly from data, and an iterative scheme is offered for the calculation of these flows. In this way a complete set of accounts can be built up from existing data. Two principles of model building using this set of accounts are then discussed. The first uses a simple definition of demographic rates, while the second uses a definition of rates which employs a concept of ‘at-risk’ populations. Procedures are given for calculating these populations. The account building principles are illustrated with a worked example for a three region system: the West Riding of Yorkshire, the rest of England and Wales, and the rest of the world. The results presented in this paper are for aggregate populations. In a subsequent paper equivalent results will be presented for age/sex disaggregated populations.
Theoretical Issues in the Design of Population Mobility Models
Authors: Morrison P A
Published: October 2006

This paper identifies major theoretical guidelines that emerge from recent migration research, and explores their bearing on model design. A conjunctive framework combining two phases is proposed. The first phase is a retention model based on a theory of differential perception and responsiveness; it portrays the decision to move in relation to a socially structured decision threshold. The second phase is an allocation model that portrays the aggregate process whereby a system of destinations compete with each other for shares of available outmigrants.
A Revised Notation for Spatial Demographic Accounts and Models
Authors: Rees P H
Published: October 2006

A revised notation is developed in which the accounting and model relationships that characterize multiregional population systems can be expressed. The variable K represents population as a stock, as a flow, and as an event count. People move from one state and location to another state and location over time. A special set of location—state labels for variable K describe the transitions possible. The hope is expressed that the notation will contribute to fruitful synthesis in the field of spatial demography.
Equilibrium Models of Cities: 2. Single-Species Cities
Authors: Amson J C
Published: October 2006

This second part of a study of a city as an ‘urban gravitational plasma’ investigates in detail the case where the city consists of only one species of civic matter, and is circularly symmetric. To increase the relevance of the theory to actual urban situations, this civic matter is assumed throughout to be a citizen population, though the theory would apply just as well if other illustrations, such as floor space or traffic flows, etc., were to be chosen instead. The population is assumed to attract itself in a way which tends to increase its density in high density regions and to decrease it in low density regions. This ‘clumping’ effect is offset by another inducement on the population to relocate itself in places where some ‘dissatisfaction potential’ is less. Again, for illustration, it is assumed throughout that the dissatisfaction has the form of a housing rental, that is, the price of the composite bundle of ‘housing’ commodities and utilities.

It is shown that the competition between the two civic forces of attraction and dispersal can lead to equilibrium distributions of the population in which the forces are everywhere in balance. The forms of these distributions depend greatly on the extent to which the housing rental is proportional to the local population density. Different degrees of this dependence are shown to give rise to many different forms of the equilibrium configurations available to a city. These are classified according to a regular scheme, and their properties explored and illustrated in detail. The manner in which one equilibrium configuration may grow into another, with or without any change in the total population in the city, leads to the idea of an ‘equilibrium growth’ in a city. Again their different possible types are examined in detail.

Finally, certain classes of the equilibrium configurations are shown to resemble closely the familiar negative exponential and gaussian distributions of population density. The resemblance can be so close as to make it extremely likely that many actual cities, that have been shown elsewhere to exhibit population density distributions of those forms, may in fact be exhibiting equilibrium distributions of the kind deduced in this study.
Measuring the Determinants of Relative House Prices
Authors: Wilkinson R K , Archer Catherine A
Published: October 2006

A model of the determinants of relative house prices was formulated and used to obtain estimates of the importance of various aspects of the dwelling and its environment. Two estimation techniques were employed: multiple regression analysis and the method of principal components. The results of the two exercises are compared and the relative efficiency of the estimation techniques is assessed in relation to the problem of multicollinearity.
The Development of an Urban Interindustry Model: 1. Building the Input—Output Accounts
Authors: Morrison W I
Published: October 2006

This is the first paper in a three part series to be published in successive issues of this journal. It discusses the implementation of an empirically based input—output model for the city of Peterborough for 1968. The nature of the model, the problems of definition, the development of control totals, the survey procedures, and the way in which the input—output table was constructed are considered in detail, both as an introduction to the later papers and because it is felt that these issues will be of sufficient interest to others engaged in similar research elsewhere.
Optimal Network Problem: A Branch-and-Bound Algorithm
Authors: Boyce D E , Farhi A , Weischedel R
Published: October 2006

The problem of selecting a subset of links so as to minimize the sum of shortest path distances between all pairs of nodes, subject to a budget constraint on total length of links, may be solved by a modification of a branch-and-bound algorithm developed for optimal variable selection problems in statistics. The modified algorithm is described in detail, and encouraging computational experience on 10 node networks is reported. The use of the algorithm as a heuristic approach to solving the optimal network problem is also discussed.
Subways and Land Use
Authors: Capozza D
Published: October 2006

This paper develops a general equilibrium model of a city with two transportation modes. One mode is land intensive, that is, roads, while the second is land economizing, that is, subways. The effects of subway construction on land values and land uses in a metropolitan area are discussed. An important implication is that, if a subway system is worth constructing, it will have a suburbanizing effect on the city. In addition there will be considerable impact on housing prices and land values, but these changes will not totally offset each other.
Mathematical Models of Industrial Plant Location and Pollution Abatement Strategies
Authors: Shefer D , Guldmann J-M
Published: October 2006

The present paper describes several mathematical models designed to control, through regulations, the locations and quantities of air pollution emissions. A Gaussian diffusion model is used in order to build an air-pollution transfer-coefficient matrix. Given the rate of increase in production and subsequently emission of air pollution, the model developed demonstrates how the permitted level of pollution emission can be set for each locality or industry, and how it is possible to assign methods of abatement and to measure their effectiveness. Finally the general abatement—location model is developed. This model simultaneously allocates industries to subareas and assigns control methods to the various industries so as to conform with the air quality standards set forth.
Future Generations and the Social Rate of Discount
Authors: Nash C A
Published: October 2006

This paper reexamines the case for discounting for time in public investment appraisal where long-term or irreversible effects on future generations are involved. It is concluded that—while, in the short-term, considerations of equity reinforce the commonly advocated case for discounting for time—in evaluating long-term or irreversible effects, current discounting procedures require the doubtful assumption of perpetual exponential growth of real income. However, if discounting were abandoned, use of the standard cost—benefit-analysis framework would require the forecasting of shadow prices for all future dates, unless an arbitrary time horizon is adopted. Thus cost—benefit analysis does not appear to be a satisfactory method for evaluating effects on future generations.
A Dynamic Disequilibrium Model of Residential Location
Authors: Anas A
Published: October 2006

Operational models of residential location have followed two separate lines of development. The gravity and maximum entropy models are characterized by operational simplicity and adaptability to disaggregated data; they remain, however, descriptive in nature. The theoretical microeconomic models, on the other hand, have delineated the concepts of competitive equilibrium and Pareto optimality in an aggregate and deterministic way. There has been an implicit need, since the development of maximum entropy models by Wilson, to bridge the gap between the descriptive and the theoretical models. As Wilson himself has asserted: “The models will only become significantly better when they are extended to incorporate a detailed knowledge of preference structures and utility functions …” (Wilson, 1969b). The present paper is a development in this direction.
A Note on the Central Place Theory
Authors: Biermann H
Published: October 2006

Although the pioneering study by Christaller (1933) has produced a flood of publications on central place theory which now extend beyond the limits of a short survey, the fact remains that these publications rest on investigations that are purely static and retrospective. Essentially the publications represent no advance on Christaller's work. They attempt, that is, to describe existing positions and to develop indicators for the identification of central place structures. In doing so these writers adopt, without exception, the concept of “excess function”(1) which was already used by Christaller to characterize central places. [A survey of Christaller's ideas can be found in Berry and Pred (1965); see also Beckmann (1968), von Böventer (1969), Gustafsson and Söker (1972), Biermann (1973a) and elsewhere.] None, however, shows how this excess function came into being, or, alternatively, how it can be explained, and whether it exhibits objective spatial stability(2). It is often overlooked, or uncritically accepted, that numerous value judgments and assumptions on the behaviour of consumers are, in addition, contained in this excess function. In other words, the discussions in these publications have no explanatory character. By the same token they contain, strictly speaking, no empirically-based theories; that is, they lack the ‘explanans' that would make it possible to forecast ensuing occurrences and phenomena (Popper, 1959).
Professor Beckerman in Perspective
Authors: Coddington A
Published: October 2006

This paper considers Professor Beckerman's view that the depletion of natural resources and the pollution of the environment create no serious threat of social disruption; pose problems which are either self-regulating or easily solved by pricing policies; and require no original thought for the understanding of the politico-economic problems involved. It is argued that Beckerman's views rest on a number of unstated acts of faith regarding the working of the politico-economic system, these being crucial to his conclusions but unsupported by his arguments.
Activity Analysis of Spatial-Allocation Models
Authors: Broadbent T A
Published: October 2006

This paper illustrates how the concept of activity analysis can be used to construct general frameworks for descriptive urban models. There is a brief introduction to the activity analysis and the representation of a multisector production-consumption system. This is followed by examples of the use of the framework with two spatial-allocation models—a singly-constrained retail model and a version of the Lowry model. These models generate coefficients within a general activity-commodity table. One insight provided by the framework is the ‘dual’ model. This provides a set of system indicators for use in the evaluation of projects which are fully consistent with the implied production and consumption system represented by the spatial-allocation model.
Possible Extensions to the Factorial Ecology Method: A Note
Authors: Johnston R J
Published: October 2006

The set of technical procedures commonly known as factorial ecology acts on a correlation matrix and so is based on variables standardised to the common base of zero mean and unit variance. This, according to the present note, is wasteful of the information on the data matrix being analysed. Alternative input matrices, to be treated as complementary to the correlation matrix, are suggested. These comprise firstly measures of variance-covariance, and secondly measures of the cross-products. Several examples of small data sets are used to illustrate the interpretative advantages of these matrices. No firm conclusions are offered, since further research is needed and unresolved problems still exist, but the possible extensions offered to the factorial ecology method seem worthy of serious consideration.
Equilibrium of Location in an Isolated State
Authors: Webber M J
Published: October 2006

This paper presents a model of the location of agricultural production. The price of output, the location of production, and the density of population are determined by the assumption of an equilibrium of exchange between the city service industry and its surrounding agricultural hinterland. The demand and supply of transport and the allocation of population to urban and rural occupations are also determined within the model.
The Decision to Pollute
Authors: Dawes R M , Delay J , Chaplin W
Published: October 2006

One way of studying the pollution problem is to examine the decision making process in situations in which gain accrues directly to an individual, while loss is spread out across the group of which the individual is a member. Such a situation has been termed a commons dilemma by Lloyd in 1833; it is a variant of the well known prisoner's dilemma. The mathematical model of rational decision making when facing the commons dilemma implies the dismal conclusion that individuals acting rationally will end up by destroying, or nearly destroying, the common wealth. Suggestions are made concerning ways in which people may be persuaded not to pollute our environment.
A Disaggregated Model of Urban Spatial Structure: Theoretical Framework
Authors: Echenique M , Feo A , Herrera R , Riquezes J
Published: October 2006

This paper describes a disaggregated model of urban spatial structure which combines the framework provided by the macroscale approach of social physics, to which most models developed to date belong, and the advantages derived from the use of the microscale approach provided by economic theory. The model attempts to integrate both approaches by means of the use of maximum entropy techniques together with concepts from microeconomic theory. The former provides an operational basis for the model, while the latter provides a theoretical explanation of the process.

At a general level the model introduces the addition of a land market submodel and a transport submodel to the framework provided by Lowry (1964). At a more detailed level the model transforms the employment in the city into economic sectors, socioeconomic groups, and income groups. This allows for the conception of the urban spatial structure in terms of a market where transactions take place between buyers and sellers of goods.

The disaggregated model presented here has been designed to provide a large number of variables which can be manipulated and controlled as part of policy decision making and planning analysis—this includes, for example, the normal planning controls such as density restriction and changes in the location of manufacturing, government, and agricultural employment. Also, the effect of changes in the costs of transport (car prices, fares, and routing) can be analysed. Taxes and subsidies on income, housing, and housing interest rates can be manipulated within the model.
A Demand Model for Leisure Travel
Authors: Vickerman R W
Published: October 2006

The nature of leisure travel is examined and a new approach to demand modelling is suggested that incorporates attraction and accessibility factors into a disaggregated trip generation model which is mode specific. Some experimental empirical estimation of a version of the model yields worthwhile results, and suggests lines for further research and development.
The Application of Behavioural Mode-Choice Models to Leisure Travel
Authors: Collings J J
Published: October 2006

Problems involved in applying the usual mode-choice modelling methods to leisure travel are discussed and a number of points are investigated empirically. It is suggested that the mode-choice model may not be useful for the analysis of a large part of leisure trip-making behaviour. However, a set of data is found for which the assumptions of the model are valid and a number of mode-choice models are estimated.
Road Networks and the Location of Facilities
Authors: Robertson Isobel M L
Published: October 2006

Procedures for solving the location-allocation problem generally embrace only straight-line distances between the facilities and the population served. Where, however, the direct distance has a varying relationship with actual distance as, for example, in Highland Scotland or in a public transport system where direct links between certain towns are absent, it seems essential to consider real road distances. The Törnqvist algorithm for locating multiple facilities was applied to Southwest Argyll, first in standard form. A modified version of the program was then devised with a new searching procedure and a subroutine to accept a complete distance matrix. Comparison of the two procedures showed that the latter gave a more realistic delineation of hinterlands.