The auxiliary region method: A hybrid method for coupling PDE- and Brownian-based dynamics for reaction-diffusion systems

Reaction-diffusion systems are used to represent many biological and physical phenomena. They model the random motion of particles (diffusion) and interactions between them (reactions). Such systems can be modelled at multiple scales with varying degrees of accuracy and computational efficiency. When representing genuinely multiscale phenomena, fine-scale models can be prohibitively expensive, whereas coarser models, although cheaper, often lack sufficient detail to accurately represent the phenomenon at hand. Spatial hybrid methods couple two or more of these representations in order to improve efficiency without compromising accuracy. In this paper, we present a novel spatial hybrid method, which we call the auxiliary region method (ARM), which couples PDE and Brownian-based representations of reaction-diffusion systems. Numerical PDE solutions on one side of an interface are coupled to Brownian-based dynamics on the other side using compartment-based "auxiliary regions". We demonstrate that the hybrid method is able to simulate reaction-diffusion dynamics for a number of different test problems with high accuracy. Further, we undertake error analysis on the ARM which demonstrates that it is robust to changes in the free parameters in the model, where previous coupling algorithms are not. In particular, we envisage that the method will be applicable for a wide range of spatial multi-scales problems including, filopodial dynamics, intracellular signalling, embryogenesis and travelling wave phenomena.Comment: 29 pages, 14 figures, 2 table

The Size and Composition of Government Expenditure

This paper tests several leading hypotheses on determinants of government expenditure. The purpose is to avoid omitted variables bias by testing the prominent theories in a comprehensive specification, to identify persistent puzzles for the current set of theories, and to explore those puzzles in greater depth by looking at the composition of government expenditure and the level of government at which it takes place as well as its magnitude. Using Global Financial Statistics data from the IMF covering over 100 countries from 1970-2000, I look at cross-sectional and inter-temporal variation in government expenditure and both individual categories of expenditure (such as defense, education, health care) and different levels of government (central, state, and local). Among other results, I find a new explanation for Wagner's Law, widespread evidence that preference heterogeneity leads to decentralization rather than outright decreases in expenditures, that a great deal of the expenditure associated with increased trade openness is not in categories that explicitly insure for risk, and evidence that both political access and income inequality affect the extent of social insurance.government expenditure, Wagner's Law

The vicious cycle: fundraising and perceived visibility in US presidential primaries

Scholars of presidential primaries have long posited a dynamic positive feedback loop between fundraising and electoral success. Yet existing work on both directions of this feedback remains inconclusive and is often explicitly cross-sectional, ignoring the dynamic aspect of the hypothesis. Pairing high-frequency FEC data on contributions and expenditures with Iowa Electronic Markets data on perceived probability of victory, we examine the bidirectional feedback between contributions and viability. We find robust, significant positive feedback in both directions. This might suggest multiple equilibria: a candidate initially anointed as the front-runner able to sustain such status solely by the fundraising advantage conferred despite possessing no advantage in quality. However, simulations suggest the feedback loop cannot, by itself, sustain advantage. Given the observed durability of front-runners, it would thus seem there is either some other feedback at work and/or the process by which the initial front-runner is identified is informative of candidate quality

Categorical Data

A very brief survey of regression for categorical data. Categorical outcome (or discrete outcome or qualitative response) regression models are models for a discrete dependent variable recording in which of two or more categories an outcome of interest lies. For binary data (two categories) probit and logit models or semiparametric methods are used. For multinomial data (more than two categories) that are unordered, common models are multinomial and conditional logit, nested logit, multinomial probit, and random parameters logit. The last two models are estimated using simulation or Bayesian methods. For ordered data, standard multinomial models are ordered logit and probit, or count models are used if ordered discrete data are actually a count.binary data, multinomial, logit, probit, count data

The Aging Population and the Size of the Welfare State: Is There a Puzzle?

Razin, Sadka, and Swagel (2002) unveil a puzzling fact: the welfare state appears to be shrinking even as the dependency ratio rises. While they formulate an elegant political economy model to explain the coexistence of an aging population and declining transfers, the resolution of the puzzle turns out to be much simpler. Labor tax rates and per capita transfers are negatively correlated with the dependency ratio in advanced economies only because this measure includes children as well as retirees. Both labor tax rates and per capita transfers in advanced economies are, in fact, historically positively correlated with the ratio of retirees to the working-age population and negatively correlated with the ratio of children to the working-age population. Increasing the number of retirees shifts preferences toward higher taxes and transfers by increasing the fraction of the population that receives transfers. In contrast, workers with more children prefer to spend more of their lifetime income while raising dependents, so they prefer smaller public pension systems. These results suggest that fiscal leakage from workers to retirees is not required to explain the broad trends in the transfer policies of advanced economies.dependency ratio, welfare state

The Information Content of Elections and Varieties of the Partisan Political Business Cycle

This event study uses economic forecasts and opinion polls to measure the response of expectations to election surprise. Use of forecast data complements older work on partisan cycles by allowing a tighter link between election and response thereby mitigating concerns of endogeneity and omitted variables. I fin that forecasters respond swiftly and significantly to election surprise. I further argue that the response ought to vary across countries with different institutional foundations. In support, I find that there exist three distinct patterns in forecasters' responses to partisan surprise corresponding to Hall and Soskice's three varieties of capitalism. In liberal market economies, forecasters expect the left to achieve jobless growth with virtually no cost to inflation. In Mediterranean market economies, forecasters expect the left to achieve deliver both higher output growth and lower unemployment but with higher inflation. And in coordinated market economies, forecasters expect the left to deliver lower growth, higher unemployment, and higher inflation.political business cycle, varieties of capitalism, forecast data, opinion polls

Did social safety net scholarships reduce drop-out rates during the Indonesian economic crisis?

The author uses regression and matching techniques to evaluate Indonesia's Social Safety Net Scholarships Program, which was developed to keep large numbers of children from dropping out of school as a result of the Asian crisis. It was expected that many families would find it difficult to keep their children in school and that dropout rates would be high, as they were during a recession in the 1980s. But dropouts did not increase markedly and enrollment rates remained relatively steady. The author examines the role the scholarship program played in producing this result. She found the scholarships to have been effective in reducing dropouts in the lower secondary school (where students are more susceptible to dropping out) by about 3 percentage points. They had no discernible impact in primary and upper secondary schools. The author also examines how well the program adhered to its documented targeting design and how effective that design was in reaching the poor. Committees that allocated the scholarships followed the criteria diligently, but a significant percentage of scholarships did go to students from households with high reported per capita expenditures, if household expenditure data are reliable. It is unclear how targeting can be improved, giving the scarcity of accurate local household data in most countries. Using local monitoring could help but then monitoring for accountability would be more difficult. Preliminary evidence favors focusing safety net scholarships--designed to reduce dropout rates during an economic crisis--on lower secondary schools, continuing to target children (especially older students) from large families, scaling back scholarships to private schools at the lower secondary level, or targeting the households hurt most by the crisis.Health Monitoring&Evaluation,Public Health Promotion,Teaching and Learning,Information Technology,Housing&Human Habitats,Health Monitoring&Evaluation,Teaching and Learning,Information Technology,Housing&Human Habitats,Primary Education