Recollapsing spacetimes with Λ<0\Lambda<0

We show that any homogeneous initial data set with $\Lambda<0$ on a product 3-manifold of the orthogonal form $(F\times \mathbb S^1,a_0^2dz^2+b_0^2\sigma^2,c_0dz^2+d_0\sigma)$, where $(F,\sigma)$ is a closed 2-surface of constant curvature and $a_0,..., d_0$ are suitable constants, recollapses under the Einstein-flow with a negative cosmological constant and forms crushing singularities at the big bang and the big crunch, respectively. Towards certain singularities among those the Kretschmann scalar remains bounded, hence these are not curvature singularities. We then show that the presence of a massless scalar field causes the Kretschmann scalar to blow-up towards both ends of spacetime for all solutions in the corresponding class. By standard arguments this recollapsing behaviour extends to an open neighborhood in the set of initial data sets and is in this sense generic close to the homogeneous regime.Comment: 28 pages, 3 figure

Spartan Daily, April 3, 1959

Volume 46, Issue 97https://scholarworks.sjsu.edu/spartandaily/3876/thumbnail.jp

Inactivity in Hungary - the persistent effect of the pension system

This paper looks at one of the major contributor to low overall employment rate in Hungary, the very low activity of the elderly. Although there are scattered pieces of evidence about the social security system in general having substantial influence on incentives and activity, the actual mechanisms are not well documented. Examining the incentive structure of the Hungarian old-age and disability pension system reveals that it provides very little to no incentive for extending active working life. Retirement through either of these pensions was and in 2006 still is an accessible exit route from the labour market that provides a minimal but secure income flow. For those reaching the minimum legal retirement age, retirement is so attractive compared to staying in the labour market that most of the working individuals retire. I use a simple model to estimate the incentives affecting the decision to retire before the legal age. Results from binary decision models estimated on household panel data support the hypothesis that incentives provided jointly by the labour market and the pension system make retirement very attractive, especially for those with bad labour market prospects. Accepting that this system was necessary to "mop up" excess labour supply in certain segments of the labour market (such as that of the extremely low-skilled individuals), it is not clear from a purely efficiency point of view why such a system is still in operation in 2006. (Remark: the government is planning to reform the system during 2007)Time Allocation and Labor Supply, Retirement; Retirement Policies, Economics of the Elderly; Economics of the Handicapped, Truncated and Censored Models

SHORT-TERM OPTIONS WITH STOCHASTIC VOLATILITY: ESTIMATION AND EMPIRICAL PERFORMANCE

This paper examines the stochastic volatility model suggested by Heston (1993). We employ a time-series approach to estimate the model and we discuss the potential effects of time-varying skewness and kurtosis on the performance of the model. In particular, it is found that the model tends to overprice out-of-the-money calls and underprice in-the-money calls. It is also found that the daily volatility risk premium presents a quite volatile behavior over time; however, our evidence suggests that the volatility risk premium has a negligible impact on the pricing performance of Heston´s model.Stochastic, Volatility, Skewness, Kurtosis, Pricing.

Spartan Daily, September 19, 1990

Volume 95, Issue 14https://scholarworks.sjsu.edu/spartandaily/8014/thumbnail.jp