On the Homogenization of Geological Fissured Systems With Curved non-periodic Cracks

We analyze the steady fluid flow in a porous medium containing a network of thin fissures i.e. width $\mathcal{O}(\epsilon)$, where all the cracks are generated by the rigid translation of a continuous piecewise $C^{1}$ functions in a fixed direction. The phenomenon is modeled in mixed variational formulation, using the stationary Darcy's law and setting coefficients of low resistance $\mathcal{O}(\epsilon)$ on the network. The singularities are removed performing asymptotic analysis as $\epsilon \rightarrow 0$ which yields an analogous system hosting only tangential flow in the fissures. Finally the fissures are collapsed into two dimensional manifolds.Comment: 24 pages, 4 figure

Gravity-driven instability in a spherical Hele-Shaw cell

A pair of concentric spheres separated by a small gap form a spherical Hele-Shaw cell. In this cell an interfacial instability arises when two immiscible fluids flow. We derive the equation of motion for the interface perturbation amplitudes, including both pressure and gravity drivings, using a mode coupling approach. Linear stability analysis shows that mode growth rates depend upon interface perimeter and gravitational force. Mode coupling analysis reveals the formation of fingering structures presenting a tendency toward finger tip-sharpening.Comment: 13 pages, 4 ps figures, RevTex, to appear in Physical Review

Understanding the Workweek of Foreign Born Workers in the United States

I analyze the length of the workweek of foreign-born workers in the U.S. I concentrate on workers supplying long hours of work − 50 or more weekly hours and document that immigrants are less likely than natives to work long hours. Surprisingly, these differences are greatest among highly educated and salary paid workers, and persists even after conditioning for demographic characteristics. I explain these differences with two within occupation characteristics. First, relative to natives, immigrants are less likely to supply long work weeks if they work in occupations where the immigrant-native earnings differential is big. Second, immigrants are also less likely to supply long work weeks when they work in occupations with a wide dispersion of earnings. This second result is important, because the occupation dispersion of earnings has been used to characterize changes of the worker's earnings over the worker life cycle (Bell and Freeman, 2001; Kuhn and Lozano, 2008), and a good measure of the incentives to supply long hours of work.hours of work, immigrants