Existence of KPP Type Fronts in Space-Time Periodic Shear Flows and a Study of Minimal Speeds Based on Variational Principle

We prove the existence of reaction-diffusion traveling fronts in mean zero space-time periodic shear flows for nonnegative reactions including the classical KPP (Kolmogorov-Petrovsky-Piskunov) nonlinearity. For the KPP nonlinearity, the minimal front speed is characterized by a variational principle involving the principal eigenvalue of a space-time periodic parabolic operator. Analysis of the variational principle shows that adding a mean-zero space time periodic shear flow to an existing mean zero space-periodic shear flow leads to speed enhancement. Computation of KPP minimal speeds is performed based on the variational principle and a spectrally accurate discretization of the principal eigenvalue problem. It shows that the enhancement is monotone decreasing in temporal shear frequency, and that the total enhancement from pure reaction-diffusion obeys quadratic and linear laws at small and large shear amplitudes

Will The Real Family-Friendly Employer Please Stand Up: Who Permits Parents To Reduce Working Hours For Purposes of Childcare?

Balancing work and family life can be a challenge, especially when a person needs to adjust her work schedule to deal with a family crisis. If the crisis involves a long term problem, such as caring for a sick or injured child that requires several months of care, the balancing act can require major shifts in the role an employee plays in a firm. This paper examines how an employer reacts to such a family-work issue: an employee who want to move from full-time to part-time in order to care for a young child. Most empirical work in this area deals with formal policies such as maternity leave, paternity leave, or leave beyond that required by the Family and Medical Leave Act and maps the type of formal policies a firm has into some "family-friendly" index. Switching from full-time to part-time is usually an informal process and it is not obvious how a firm ranking high on an index based of formal "family-friendly" policies would respond to such a request. Indeed, organizations with codified formal policies may be precisely the kinds of employers who do not permit such a shift from full-time to part-time. This is in fact what we find. Larger organizations are much more likely to provide formal policies such as paid maternity and paternity leave, while establishments that are not part of larger organizations are more likely to permit an employee to shift to part-time in order to care for a young child. These results suggests that family-friendly indexes that are based on formal policies may be unfairly labelling smaller firms "unfriendly" towards families simply because they use informal approaches to deal with family crises.

Salience, Risky Choices and Gender

Risk theories typically assume individuals make risky choices using probability weights that differ from objective probabilities. Recent theories suggest that probability weights vary depending on which portion of a risky environment is made salient. Using experimental data we show that salience affects young men and women differently, even after controlling for cognitive and non-cognitive skills. Men are significantly more likely than women to switch from a certain to a risky choice once the upside of winning is made salient, even though the expected value of the choice remains the same.gender, salience, risk-aversion, probability weights, cognitive ability

Vulnerability, Unemployment and Poverty: A Class of Distribution and Sensitive Measures, Its Axiomatic Properties and Applications

Measures of unemployment and poverty have tended to focus solely on those currently unemployed or below the poverty line. This approach has ignored the members of society that are vulnerable to becoming unemployed or falling into poverty. Current literature in this area has implicitly assumed that since someone who is vulnerable experiences pain from the chance of becoming unemployed or falling into poverty, our standard measures of unemployment and poverty do not accurately account for this pain. The implication is that vulnerability is a `bad' and policies should aim to reduce the number of people who are vulnerable in a society. In this paper we argue that, at the macro level, vulnerability can be viewed as a �good� because, with unemployment remaining constant, the presence of vulnerable people implies that there must also exist currently unemployed people who expect to find work in the near future. And a society where unemployment is more equitably shared is better than a society where the burden of unemployment is carried by only a few. Given this view of vulnerability we then suggest a class of measures that, unlike the standard unemployment rate, account for the amount of vulnerability that exists in a society. We show some attractive axioms that our measure satisfies, fully characterize our measure and apply it to data from the U.S. and South Africa.