Conserved Linking in Single- and Double-Stranded Polymers

We demonstrate a variant of the Bond Fluctuation lattice Monte Carlo model in which moves through cis conformations are forbidden. Ring polymers in this model have a conserved quantity that amounts to a topological linking number. Increased linking number reduces the radius of gyration mildly. A linking number of order 0.2 per bond leads to an eight-percent reduction of the radius for 128-bond chains. This percentage appears to rise with increasing chain length, contrary to expectation. For ring chains evolving without the conservation of linking number, we demonstrate a substantial anti-correlation between the twist and writhe variables whose sum yields the linking number. We raise the possibility that our observed anti-correlations may have counterparts in the most important practical polymer that conserves linking number, DNA.Comment: Revised title, minor changes, updated references. 36 pages, including 14 figures. More formats available at http://rainbow.uchicago.edu/~plewa/webpaper

Low cost management of replicated data in fault-tolerant distributed systems

Many distributed systems replicate data for fault tolerance or availability. In such systems, a logical update on a data item results in a physical update on a number of copies. The synchronization and communication required to keep the copies of replicated data consistent introduce a delay when operations are performed. A technique is described that relaxes the usual degree of synchronization, permitting replicated data items to be updated concurrently with other operations, while at the same time ensuring that correctness is not violated. The additional concurrency thus obtained results in better response time when performing operations on replicated data. How this technique performs in conjunction with a roll-back and a roll-forward failure recovery mechanism is also discussed

An Intergenerational Model of Wages, Hours and Earnings

In this paper we develop and estimate a factor model of the earnings, labor supply, and wages of young men and young women, their parents and their siblings. We estimate the model using data on matched sibling and parent-child pairs from the National Longitudinal Survey of Labor Market Experience. We measure the extent to which a set of unobserved parental and family factors that drive wage rates and work hours independently of wage rates lead to similarities among family members in labor market outcomes. We find strong family similarities in work hours that run along gender lines. These similarities are primarily due to preferences rather than to labor supply responses to family similarities in wages. The wage factors of the father and mother influence the wages of both sons and daughters. A `sibling' wage factor also plays an important role in wage determination. We find that intergenerational correlations in wages substantially overestimate the direct influence of fathers, and especially mothers, on wages. This is because the father's and mother's wage factors are positively correlated. The relative importance for the variance in earnings of the direct effect of wages, the labor supply response induced by wages, and effect of hours preferences varies by gender, and by age in the case of women. For all groups most of the effect of wages on earnings is direct rather than through a labor supply response.