WP 37 - Search, mismatch and unemployment

This paper explores the efficiency of the equilibrium allocation in a matching model with heterogeneous workers and jobs. In the basic setup the labor force is divided in two groups. The high-skill workers are qualified for all jobs, while low-skill workers can perform unskilled jobs but not the more attractive skilled jobs. We demonstrate that the equilibrium with random search and ex post bargaining is never efficient. Under Hosios’ condition the average wage is correct, but bargaining compresses the wage distribution relative to workers’ shadow values. The wage compression distorts the relative profits of jobs making it too attractive to create skilled jobs. Furthermore, the low skill premium may prevent that the two types of workers efficiently sort in different jobs. In the first case we show that the market offers too few job opportunities for low-skill workers. On the contrary, when mismatch is socially wasteful, we find that low-skill workers experience shorter unemployment spells than in the efficient allocation. Finally, we show that our results generalize to environments with many types of agents and less stringent restrictions on the production technology.

Core-crust transition pressure for relativistic slowly rotating neutron stars

We study the influence of core-\textit{crust} transition pressure changes on the general dynamical properties of neutron star configurations. First we study the matching conditions in core-\textit{crust} transition pressure region, where phase transitions in the equation of state causes energy density jumps. Then using a surface \textit{crust} approximation, we can construct configurations where the matter is described by the equation of state of the core of the star and the core-\textit{crust} transition pressure. We will consider neutron stars in the slow rotation limit, considering perturbation theory up to second order in the angular velocity so that the deformation of the star is also taken into account. The junction determines the parameters of the star such as total mass, angular and quadrupolar momentum.Comment: 4 pages, 1 figur

E. Rodríguez Almeida: Los Tituli Picti de las ánforas olearias de la Bética I, Madrid, Editorial de la Universidad Complutense, 1989, 218 Pp. + 83 figs

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Claude Domergue: Les mines de la Péninsule Ibérique dans l’Antiquité Romaine, Roma. Ecole Fran9aise de Rome. 1990, 625 + 32 láms. + 52 figuras + 6 mapas

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Composites Based on Poly(Lactic Acid) (PLA) and SBA-15: Effect of Mesoporous Silica on Thermal Stability and on Isothermal Crystallization from Either Glass or Molten State

© 2020 by the authors.Several composites based on an L-rich poly(lactic acid) (PLA) with different contents of mesoporous Santa Barbara Amorphous (SBA-15) silica were prepared in order to evaluate the effect of the mesoporous silica on the resultant PLA materials by examining morphological aspects, changes in PLA phases and their transitions, and, primarily, the influence on some final properties. Melt extrusion was chosen for the obtainment of the composites, followed by quenching from the melt to prepare films. Completely amorphous samples were then attained, as deduced from X-ray diffraction and differential scanning calorimetry (DSC) analyses. Thermogravimetric analysis (TGA) results demonstrated that the presence of SBA-15 particles in the PLA matrix did not exert any significant influence on the thermal decomposition of these composites. An important nucleation effect of the silica was found in PLA, especially under isothermal crystallization either from the melt or from its glassy state. As expected, isothermal crystallization from the glass was considerably faster than from the molten state, and these high differences were also responsible for a more considerable nucleating role of SBA-15 when crystallizing from the melt. It is remarkable that the PLA under analysis showed very close temperatures for cold crystallization and its subsequent melting. Moreover, the type of developed polymorphs did not accomplish the common rules previously described in the literature. Thus, all the isothermal experiments led to exclusive formation of the α modification, and the observation of the α’ crystals required the annealing for long times at temperatures below 80 °C, as ascertained by both DSC and X-ray diffraction experiments. Finally, microhardness (MH) measurements indicated a competition between the PLA physical aging and the silica reinforcement effect in the as-processed amorphous films. Physical aging in the neat PLA was much more important than in the PLA matrix that constituted the composites. Accordingly, the MH trend with SBA-15 content was strongly dependent on aging times.This research was funded by AEI/FEDER, UE (grant number MAT2016-79869-C2-1-P) and ALBA Synchrotron Light Facility. TMDR is also grateful for her pre-doctoral funding (contract number BES-2017-082284).Peer reviewe