On the optical-mechanical analogy in general relativity

We demonstrate that the Evans-Rosenquist formulation of the optical mechanical analogy, so successful in the application to classical problems, also describes the motion of massless particles in the Schwarzschild field of general relativity. It is possible to obtain the well known equations for light orbit and radar echo delay which account for two exclusive tests of Einstein's field equations. Some remarks including suggestions for future work are also added.Comment: Uploaded on arxiv for the benefit of the researcher

Anomalous Chiral Action from the Path-Integral

By generalizing the Fujikawa approach, we show in the path-integral formalism: (1) how the infinitesimal variation of the fermion measure can be integrated to obtain the full anomalous chiral action; (2) how the action derived in this way can be identified as the Chern-Simons term in five dimensions, if the anomaly is consistent; (3) how the regularization can be carried out, so as to lead to the consistent anomaly and not to the covariant anomaly. Our method uses Schwinger's ``proper-time'' representation of the Green's function and the gauge invariant point-splitting technique. We find that the consistency requirement and the point-splitting technique allow both an anomalous and a non-anomalous action. In the end, the nature of the vacuum determines whether we have an anomalous theory, or, a non-anomalous theoryComment: 28 page

Microtubule nucleotide requirements : the role of nucleoside diphosphate kinase

Imperial Users onl

The impacts of flooding and methods of assessment in urban areas of Bangladesh

This research is the first of its kind in Bangladesh. It focuses upon flood losses in urban sectors of the country’s economy. The broad research question is whether flood impacts in urban or non-agricultural sectors are important in Bangladesh, given that it is currently an agricultural economy. The research examines the applicability of existing urban flood impact assessment methods, and develops methods suitable to Bangladesh. An important aim is to accumulate a knowledge base of flood impacts in the urban or non-agricultural sectors. With appropriate modifications, flood loss assessment methods generated in developed countries may be applied in a developing country such as Bangladesh. However, the ‘synthetic’ approach of constructing standard potential flood loss data sets is not feasible. Using surveys of actual floods, the construction of reasonably high-quality ‘average’ data sets proves to be feasible, as floods in Bangladesh are not sparse. The construction of data sets through regressions is preferred because it is more realistic and cost-effective. The widely used unit-loss model is found to be applicable to appraisals of urban protection schemes. However, the successful application of the model depends on the accuracy of land use and land level survey data, and detailed hydraulic and hydrological information. In Bangladesh, this form of modelling is found to be suitable for project appraisals ranging from small to intermediate scale. Some methods, however, are suitable for up to full scale appraisals. The major achievement of the research is that flood loss potential for urban Sectors has been thoroughly investigated, providing flood loss data of a significantly higher quality that are available hitherto in Bangladesh. In providing these data the research is a significant advance upon the methods recommended within the existing FPCO Guidelines for project assessment, and those used in recent FAP urban protection studies. The assessments methods developed and the standard damage data sets constructed may now be used to appraise urban protections, which will also facilitate evaluation of agricultural projects more comprehensively through incorporating non-agricultural losses that can be averted in such schemes. The research reveals that the urban sectors of the economy are highly vulnerable to floods. Induced by rapid urbanisation, potential urban flood losses in Bangladesh are expected to be progressively more important in the future. Poverty is found to be fundamental to flood hazard vulnerability: the poorest of the poor have the most to lose in proportional (to value) terms. A high priority can now be given to protect urban and commercial centres in Bangladesh. Given limited resources in Bangladesh, low-cost non-structural measures are also important. Local knowledge and informal flood warning systems have a positive bearing on resilience building. Community cohesion, together with family kinships, are also important in this respect. Different types of floods (e.g. river flood, flash flood and tidal surge) are associated with differential impacts: tidal floods prove the most destructive. Flood impacts at the macro-level are not found to be as severe as those at the micro-level. The findings suggest that floods deepen poverty and help widen the income gap between rich and poor. This problem poses further research questions regarding ‘equity’ and sustainable development. Project appraisal methods using conventional ‘economic efficiency analysis’ need to be re-calibrated in order to confront the problems relating to inequity and sustainable development, especially in the context of existing socio-economic conditions in Bangladesh

Skilled Immigration and Wages in Australia*

This paper addresses the implications of the increasing skill intensity of cross-border migration flows for labour market outcomes in host countries. Specifically, we investigate the impact of the relative growth of skilled migrants on domestic wages in Australia over the last quarter century (1980-2006). We use instrumental variable (IV) estimation techniques to deal with the potential endogeneity of immigration. Unlike most of the previous literature, we use macro data to allow for the adjustment of wages and aggregate demand to immigration flows. However, the limited time span of such data raises problems of small sample bias. We address the small sample bias problem by using Jackknife IV estimation. Our basic finding challenges popular presumptions about the adverse wage implications of immigration. However, our examination of the skill composition of migration flows supports the many prevailing empirical findings that immigration need not cause labour market outcomes to deteriorate. Specifically, we do not find any robust evidence that a relative increase in arrivals of skilled immigrants exerts discernible adverse consequences on wages in Australia.Immigration, wage, endogeneity, instrumental variable.

Cylindrically symmetric wormholes

This paper discusses traversable wormholes that differ slightly but significantly from those of the Morris-Thorne type under the assumption of cylindrical symmetry. The throat is a piecewise smooth cylindrical surface resulting in a shape function that is not differentiable at some value. It is proposed that the regular derivative be replaced by a one-sided derivative at this value. The resulting wormhole geometry satisfies the weak energy condition.Comment: Supplied missing figures; 15 pages AMSTe