Non-positive curvature and the Ptolemy inequality

We provide examples of non-locally compact geodesic Ptolemy metric spaces which are not uniquely geodesic. On the other hand, we show that locally compact, geodesic Ptolemy metric spaces are uniquely geodesic. Moreover, we prove that a metric space is CAT(0) if and only if it is Busemann convex and Ptolemy.Comment: 11 pages, 2 figure

Identifying spatial efficiency-equity tradeoffs in territorial development policies : evidence from Uganda

In many countries, place specific investments in infrastructure are viewed as integral components of territorial development policies. But are these policies fighting market forces of concentration? Or are they adding net value to the national economy by tapping underexploited resources? This paper contributes to the debate on the spatial allocation of infrastructure investments by examining where these investments will generate the highest economic returns"spatial efficiency", and identifying whether there re tradeoffs when infrastructure coverage is made more equitable across regions"spatial equity". The empirical analysis focuses on Uganda and is based on estimating models of firm location choice, drawing on insights from the new economic geography literature. The main findings show that establishments in the manufacturing industry gain from being in areas that offer a diverse mix of economic activities. In addition, availability of power supply, transport links connecting districts to markets, and the supply of skilled workers attract manufacturing activities. Combining all these factors gives a distinct advantage to existing agglomerations along leading areas around Kampala and Jinja. Infrastructure investments in these areas are likely to produce the highest returns compared with investments elsewhere. Public infrastructure investments in other locations are likely to attract fewer private investors, and will pose a spatial efficiencyequity tradeoff. To better integrate lagging regions with the national economy, lessons from the WDR2009"Reshaping Economic Geography"calling for investments in health and education in lagging areas are likely to be more beneficial.Transport Economics Policy&Planning,E-Business,Banks&Banking Reform,Non Bank Financial Institutions,Economic Theory&Research

A Guide to Disability Statistics from the Panel Study of Income Dynamics

This User Guide provides information on the Panel Study of Income Dynamics (PSID). The 2003 PSID is a nationally representative sample of over 7,000 families. The PSID began in 1968 with a sample of 4,800 families and re-interviewed these families on an annual basis from 1968-1997. Since then, it has re-interviewed them biennially. Following the same families and individuals since 1968, the PSID collects data on economic, health, and social behavior. (See http://psidonline.isr.umich.edu/ for detailed information on the PSID). Initially, the PSID identified disability by asking the head of the household whether he, or she when no adult male is present, had a physical or nervous condition that limits his or her ability to work. In 1981 the PSID began asking the head this question with respect to his spouse. Additional questions that provide an opportunity to expand this definition of disability were included in 2003. The User Guide makes use of these new questions to estimate the size of the population with disabilities and the prevalence rate of disability in the population, as well as the employment rate and level of economic well-being. The major strength of the PSID for those interested in disability research is its long-running information on families. No other nationally representative survey has captured such detailed information on the same families over such a long time. Such longitudinal data allows researchers to better understand the dynamics of the disability process and its consequences. Here we demonstrate the comparative advantage of the PSID over traditional cross-sectional data sets. Using the PSID, we identify persons with disabilities of various lengths and show the sensitivity of alternative definitions of the population with disabilities based on the duration of a disability. We also measure how the employment and economic well-being of individuals changes following the onset of a disability. Finally, we provide examples of how the PSID has been used with the German Socio-Economic Panel (GSOEP) to compare the employment and economic well-being of working-age people with disabilities in the United States and Germany. This analysis uses the equivalized data from these longitudinal datasets contained in the Cornell University Cross-National Equivalent File (CNEF)

Energies of Quantum QED Flux Tubes

In this talk I present recent studies on vacuum polarization energies and energy densities induced by QED flux tubes. I focus on comparing three and four dimensional scenarios and the discussion of various approximation schemes in view of the exact treatment.Comment: 9 pages latex, Talk presented at the QFEXT 05 workshop in Barcelona, Sept. 2005. To appear in the proceeding