The scaling of exploding liquid jets under intense X-ray pulses

A general scaling of the evolution of an exploding liquid jet under an ultra short and intense X-ray pulse from a X-ray free electron laser (XFEL) is proposed. A general formulation of the conservation of energy for blasts in vacuum partially against a deformable object leads to a compact expression that governs the evolution of the gap produced by the explosion. The theoretical analysis contemplates two asymptotic stages for small and large times from the initiation of the blast. A complete dimensional analysis of the problem and an optimal collapse of experimental data reveal that the universal approximate analytical solution proposed is in remarkable agreement with experiments

Kinetic approach to the cluster liquid-gas transition

The liquid-gas transition in free atomic clusters is investigated theoretically based on simple unimolecular rate theories and assuming sequential evaporations. A kinetic Monte Carlo scheme is used to compute the time-dependent properties of clusters undergoing multiple dissociations, and two possible definitions of the boiling point are proposed, relying on the cluster or gas temperature. This numerical approach is supported by molecular dynamics simulations of clusters made of sodium atoms or C60 molecules, as well as simplified rate equation

Theoretical study of finite temperature spectroscopy in van der Waals clusters. II Time-dependent absorption spectra

Using approximate partition functions and a master equation approach, we investigate the statistical relaxation toward equilibrium in selected CaAr$_n$ clusters. The Gaussian theory of absorption (previous article) is employed to calculate the average photoabsorption intensity associated with the 4s^2-> 4s^14p^1 transition of calcium as a function of time during relaxation. In CaAr_6 and CaAr_10 simple relaxation is observed with a single time scale. CaAr_13 exhibits much slower dynamics and the relaxation occurs over two distinct time scales. CaAr_37 shows much slower relaxation with multiple transients, reminiscent of glassy behavior due to competition between different low-energy structures. We interpret these results in terms of the underlying potential energy surfaces for these clusters.Comment: 10 pages, 9 figure

Fear of Floating

In recent years, many countries have suffered severe financial crises, producing a staggering toll on their economies, particularly in emerging markets. One view blames fixed exchange rates-- soft pegs'--for these meltdowns. Adherents to that view advise countries to allow their currency to float. We analyze the behavior of exchange rates, reserves, the monetary aggregates, interest rates, and commodity prices across 154 exchange rate arrangements to assess whether official labels' provide an adequate representation of actual country practice. We find that, countries that say they allow their exchange rate to float mostly do not--there seems to be an epidemic case of fear of floating.' Since countries that are classified as having a free or a managed float mostly resemble noncredible pegs--the so-called demise of fixed exchange rates' is a myth--the fear of floating is pervasive, even among some of the developed countries. We present an analytical framework that helps to understand why there is fear of floating.

Social Networks in Labor Markets

Research in sociology and economics point to important role for social networks in labor markets. Social contacts mediate propagation of rich and reliable information among indi- viduals and thus help workers find jobs and employers find employees. Recent theoretical advances show that for agents connected through networks employment is positively cor- related across time and agents, unemployment exhibits duration dependence, and inequal- ity can persist. Recent empirical findings underscore nonlinearities in social interactions and potentially important effects of self-selection. Socioeconomic characteristics can explain substantial spatial dependence in unemployment.networks, labor markets, social connections, unemployment, proximity, spatial dependence, information networks, neighborhoods and jobs

Dynamic recrystallization mechanisms and twining evolution during hot deformation of Inconel 718

The hot deformation behavior of an IN718 superalloy was studied by isothermal compression tests under the deformation temperature range of 950–1100 °C and strain rate range of 0.001–1 s-1 up to true strains of 0.05, 0.2, 0.4 and 0.7. Electron backscattered diffraction (EBSD) technique was employed to investigate systematically the effects of strain, strain rate and deformation temperature on the subgrain structures, local and cumulative misorientations and twinning phenomena. The results showed that the occurrence of dynamic recrystallization (DRX) is promoted by increasing strain and deformation temperature and decreasing strain rate. The microstructural changes showed that discontinuous dynamic recrystallization (DDRX), characterized by grain boundary bulging, is the dominant nucleation mechanism in the early stages of deformation in which DRX nucleation occurs by twining behind the bulged areas. Twin boundaries of nuclei lost their ¿3 character with further deformation. However, many simple and multiple twins can be also regenerated during the growth of grains. The results showed that continuous dynamic recrystallization (CDRX) is promoted at higher strains and large strain rates, and lower temperatures, indicating that under certain conditions both DDRX and CDRX can occur simultaneously during the hot deformation of IN718.Peer ReviewedPostprint (author's final draft