Zipfs Law for Cities: An Empirical Examination

We use data for metro areas in the United States, from the US Census for 1900 û 1990, to test the validity of Zipf's Law for cities. Previous investigations are restricted to regressions of log size against log rank. In contrast, we use a nonparametric procedure to calculate local Zipf exponents from the mean and variance of city growth rates. This also allows us to test for the validity of Gibrat's Law for city growth processes. Despite variation in growth rates as a function of city size, Gibrat's Law does hold. In addition the local Zipf exponents are broadly consistent with Zipf's Law. Deviations from Zipf's Law are easily explained by deviations from Gibrat's Law.Urban growth, Zipfs Law, Gibrats Law, estimation of Brownian motion

Cross Sectional Evolution of the US City Size Distribution

We report nonparametrically estimated stochastic transition kernels for the evolution of the distribution of US metropolitan area populations, for the period 1900 to 1990. These suggest a fair amount of uniformity in the patterns of mobility during the study period. The distribution of city sizes is predominantly character-sed by persistence. Additional kernel estimates do not reveal any stark differences in intra-region mobility patterns. We characterise the nature of intra-size distribution dynamics by means of measures that do not require discretisation of the city size distribution. We employ these measures to study the degree of mobility within the US city size distribution and, separately, within regional and urban subsystems. We find that different regions show different degrees of intra-distribution mobility. Second-tier cities show more mobility than top-tier cities.City size distribution, cross-sectional evolution, intradistribution mobility

Spatial Evolution of the US Urban System

We test implications of economic geography models for location, size and growth of cities with US Census data for 1900 û 1990. Our tests involve non-parametric estimations of stochastic kernels for the distributions of city sizes and growth rates, conditional on various measures of market potential and on features sizes of neighbors. We show that while these relationships change during the twentieth century, by 1990 they stabilize such that the size distribution of cities conditional on a range of spatial variables are all roughly independent of these conditioning variables. In contrast, similar results suggest that there is a spatial element to the city wage distribution. Our parametric estimations for growth rates against market potential, entry of neighbors, and own lagged population imply a negative effect of market potential on growth rates, unless own lagged population is also included, in which case market potential has a positive effect and own lagged population a negative one. Cities grow faster when they are small relative to their market potential. In total, our results support some theoretical predictions, but also provide a number of interesting puzzles.Urban growth, spatial evolution, economic geography

The Effect of Information and Communication Technologies on Urban Structure

The geographic concentration of economic activity occurs because transport costs for goods, people and ideas give individuals and organisations incentives to locate close to each other. Historically, all of these costs have been falling. Such changes could lead us to predict the death of distance. This paper is concerned with one aspect of this prediction: the impact that less costly communication and transmission of information might have on cities and the urban structure. We develop a model which suggests that improvements in ICT will increase the dispersion of economic activity across cities making city sizes more uniform. We test this prediction using cross country data and find empirical support for this conclusion.ICT, urban structure, cross country data

Wages and employment in a random social network with arbitrary degree distribution

Empirical studies of labor markets show that social contacts are an important source of job-related information [Ioannides and Loury (2004)]. At the same time, wage differences among workers may be explained only in part by differences in individual background characteristics. Such findings motivate our model in which differences in social connectedness among otherwise identical workers result in wage inequality and differences in unemployment rates. The paper is related to theoretical contributions by Calvo- Armengol and Jackson (2004) and Calvo-Armengol and Zenou (2005) and builds on the Pissarides (2000) model. Workers may hear about job openings directly from employers or through their social contacts. We go further by introducing heterogeneity in the number of contacts each worker has with others, i.e. in the workers' degree. We utilize results from the technical literature on random graphs with arbitrary degree distributions [Newman, (2003a)] to account for a consequence of workers' receiving information about job openings from their social contacts: they compete with their social contacts' other contacts. For social networks with arbitrary degree distributions we show that people who are better connected receive a higher wage on average and face a lower unemployment rate. Numerical computations for the specific case in which connections follow a Poisson distribution show that variability in connections can result in substantial variation in the above labor market outcomes

Diffuse precordial ST-segment elevation in inferior-right myocardial infarction

A right ventricular (RV) myocardial infarction (MI) may yield precordial ST-segment elevation (STE). Accordingly, combined inferior and precordial STE may be produced during an inferior-RV MI. Such an electrocardiographic picture may be mistakenly regarded as showing wrapped left anterior descending artery (LADA) occlusion or double vessel occlusion. We present a patient with inferior-RV MI and STE in the inferior, all precordial and right chest leads, in whom the diffuse precordial STE was probably mistakenly regarded as showing anterior MI. However, the STE resolution in V1-V2 and late R’ wave in V1, which were combined with a recanalized RV branch, favored the RV origin of this STE. Furthermore, the LADA was patent when V3-V6 showed severe ischemia, while its lesion was angiographically stable. Thus its simultaneous occlusion was unlikely. The late R’ wave in V1 indicates RV transmural conduction delay;as highlighted herein, it is diagnostic of a RV myocardial infarction. (Cardiol J 2010; 17, 6: 628-631

Cyprus' image—a sun and sea destination—as a detrimental factor to seasonal fluctuations. Exploration into motivational factors for holidaying in Cyprus

Cyprus is established as a summer destination. To aid the destination in developing its winter season as well, this research uses a qualitative inductive approach to explore the tourists’ current image of the island and their motivations of visiting it. The research indicates that the current image, which essentially portrays Cyprus as a sun-and-sea destination is thought to dissuade tourists from perceiving the island as a year-round destination. Nonetheless, increasing the pull factors of the destination through the development of unique special interest products can help in extending the tourism season as well as broaden its narrow image