Market Concentration, Macroeconomic Uncertainty and Monetary Policy.

This paper studies the effect of market structure and macroeconomic uncertainty on the transmission of monetary policy. We motivate our analysis with a simple model which predicts that: 1) investment and production in more concentrated sectors are more affected by demand changes and 2) high uncertainty makes investment and production more sensitive to demand changes. The empirical analysis estimates the effect of monetary shocks on sectoral output for different sectors in the US using different structural vector autoregressive VAR approaches. The results are largely consistent with the proposed theory.Market concentration, macroeconomic uncertainty, monetary policy transmission, vector autoregressive models.

Low-temperature anomalies of a vapor deposited glass

We investigate the low temperature properties of two-dimensional Lennard-Jones glass films, prepared in silico both by liquid cooling and by physical vapor deposition. We identify deep in the solid phase a crossover temperature $T^*$, at which slow dynamics and enhanced heterogeneity emerge. Around $T^*$, localized defects become visible, leading to vibrational anomalies as compared to standard solids. We find that on average, $T^*$ decreases in samples with lower inherent structure energy, suggesting that such anomalies will be suppressed in ultra-stable glass films, prepared both by very slow liquid cooling and vapor deposition.Comment: 10 pages including appendices, 8 figures. Version accepted for Physical Review Material

q-State Potts model metastability study using optimized GPU-based Monte Carlo algorithms

We implemented a GPU based parallel code to perform Monte Carlo simulations of the two dimensional q-state Potts model. The algorithm is based on a checkerboard update scheme and assigns independent random numbers generators to each thread. The implementation allows to simulate systems up to ~10^9 spins with an average time per spin flip of 0.147ns on the fastest GPU card tested, representing a speedup up to 155x, compared with an optimized serial code running on a high-end CPU. The possibility of performing high speed simulations at large enough system sizes allowed us to provide a positive numerical evidence about the existence of metastability on very large systems based on Binder's criterion, namely, on the existence or not of specific heat singularities at spinodal temperatures different of the transition one.Comment: 30 pages, 7 figures. Accepted in Computer Physics Communications. code available at: http://www.famaf.unc.edu.ar/grupos/GPGPU/Potts/CUDAPotts.htm

Educación ambiental no formal en áreas inundables del noreste argentino

Fil: De Francesco, Fernando. Facultad de Ciencias Agrarias y Forestales, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La PlataFil: Schnack, Juan Alberto. Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plat

Analysis of the performance of polarimetric PSI over distributed scatterers with Sentinel-1 data

Sentinel−1 (S1) data enables effective monitoring of displacements using persistent scatterer interferometry (PSI). S1 includes VV and VH polarization channels, allowing us to apply polarimetric techniques to PSI. In short, polarimetric PSI (PolPSI) exploits the available polarization channels to enhance the identification and processing of measurement points including persistent scatterers (PS) and distributed scatterers (DS). Previous works have shown the benefits of using PolPSI for PS points with S1 data, but the corresponding analysis for DS is missing. DS points are processed by finding a neighborhood of statistically homogeneous pixels (SHP) and averaging the phase within that neighborhood. In this work we show how dual-polarimetric data are stricter on the selection of the SHP group than single-polarimetric data. Thanks to the information added by the second channel, different land covers are not mixed in the SHP group. As a result, the number of points in the SHP groups is generally smaller than with VV alone, but they are more reliable. The impact of this strategy on the resulting deformation estimates is also investigated in this work, showing that the deformation areas are fully preserved and the influence of nearby pixels associated with other scene elements is avoided.This work was supported in part by the European Funds for Regional Development and by the Spanish Ministry of Science and Innovation (Agencia Estatal de Investigación, AEI) with Project PID2020-117303GB-C22/AEI/10.13039/501100011033, and in part by the Generalitat Valenciana, Conselleria de Innovacion, Universidades, Ciencia y Sociedad Digital with Project CIAICO/2021/335. The research was also partially performed in the ESA-MOST China DRAGON-5 project ref. 59339

From caging to Rouse dynamics in polymer melts with intramolecular barriers: a critical test of the Mode Coupling Theory

By means of computer simulations and solution of the equations of the Mode Coupling Theory (MCT), we investigate the role of the intramolecular barriers on several dynamic aspects of non-entangled polymers. The investigated dynamic range extends from the caging regime characteristic of glass-formers to the relaxation of the chain Rouse modes. We review our recent work on this question, provide new results and critically discuss the limitations of the theory. Solutions of the MCT for the structural relaxation reproduce qualitative trends of simulations for weak and moderate barriers. However a progressive discrepancy is revealed as the limit of stiff chains is approached. This disagreement does not seem related with dynamic heterogeneities, which indeed are not enhanced by increasing barrier strength. It is not connected either with the breakdown of the convolution approximation for three-point static correlations, which retains its validity for stiff chains. These findings suggest the need of an improvement of the MCT equations for polymer melts. Concerning the relaxation of the chain degrees of freedom, MCT provides a microscopic basis for time scales from chain reorientation down to the caging regime. It rationalizes, from first principles, the observed devations from the Rouse model on increasing the barrier strength. These include anomalous scaling of relaxation times, long-time plateaux, and non-monotonous wavelength dependence of the mode correlators.Comment: 15 pages, 14 figure

Weyl-Gauge Symmetry of Graphene

The conformal invariance of the low energy limit theory governing the electronic properties of graphene is explored. In particular, it is noted that the massless Dirac theory in point enjoys local Weyl symmetry, a very large symmetry. Exploiting this symmetry in the two spatial dimensions and in the associated three dimensional spacetime, we find the geometric constraints that correspond to specific shapes of the graphene sheet for which the electronic density of states is the same as that for planar graphene, provided the measurements are made in accordance to the inner reference frame of the electronic system. These results rely on the (surprising) general relativistic-like behavior of the graphene system arising from the combination of its well known special relativistic-like behavior with the less explored Weyl symmetry. Mathematical structures, such as the Virasoro algebra and the Liouville equation, naturally arise in this three-dimensional context and can be related to specific profiles of the graphene sheet. Speculations on possible applications of three-dimensional gravity are also proposed.Comment: 22 pages, 3 figures - two new references and few typos fixed, matches published version by Annals of Physic

Preparation of poly(thiourethane) thermosets by controlled thiol-isocyanate click reaction using a latent organocatalyst

Different poly(thiourethane) thermosets were prepared by means of a thiol-isocyanate click reaction starting from three diisocyanates with different structure (isophorone diisocyanate, IPDI, 4,4'-methylene bis(cyclohexy isocyanate), HMDI and hexamethylene diisocyanate, HDI, and a tetrathiol, pentaerythritol tetrakis(3-mercap- topropionate), PETMP. The curing process has been catalyzed by basic and acid catalysts. The use of a thermally activated base generator (1-methylimidazolium tetraphenylborate, BG1MI), which is an organocatalyst, allowed a better control on the curing initiation than those traditionally used dibutyltin dilaurate (DBTDL) or tertiary amines. The curing evolution was investigated by DSC and FTIR spectroscopy. The materials obtained were characterized by thermomechanical and mechanical tests. Homogeneous ma- terials were obtained in all cases. The chemical structure of the network was correlated with the thermal and mechanical data determined. T g values in the range of 75 to 150 °C were obtained. The thermal degradation of these materials has also been investigated and a complex degradation mechanism, with three different steps was observed in all cases. These materials showed a higher thermal stability than their oxygen counterparts did. The thermosets obtained using the latent organocatalyst have similar characteristics to the ones obtained by using the common DBTDLPostprint (author's final draft

Recyclable poly(thiourethane) vitrimers with high Tg. Influence of the isocyanate structure

Networked poly(thiourethane) materials with Tgs around 130 °C, derived from two aliphatic isocyanates (isophorone diisocyanate, IPDI and 4,4'-methylene bis(cyclohexyl isocyanate), HMDI) and one aromatic diisocyanate (toluene-2,4-diisocyanate, TDI) have been prepared with the same trithiol as comonomer (trimethylol propane tris(3-mercaptopropionate), S3) in stoichiometric proportions in the presence of dibutyltin dilaurate (DBTDL) as the catalyst. The higher reactivity of TDI allowed the preparation of this material in absence of catalyst. The evolution of the curing process has been followed by FTIR. Thermomechanical studies have been performed to determine their viscoelastic properties and their vitrimeric behaviour. The materials were able to reach a complete relaxation stress state thanks to the exchange process of the thiourethane moiety. Among them, TDI derived material experimented the fastest relaxation. The materials were also characterized by thermogravimetry and tensile tests. The recycled materials obtained by grinding the original thermosets and hot-pressing the powder have been fully characterized by mechanical, thermomechanical and FTIR studies, which allowed to confirm their recyclability without appreciable changes in the network structure. The presence of DBTDL in the materials has been proved to be necessary to reach a good recyclability.Postprint (author's final draft

Actuator behaviour of tailored poly(Thiourethane) shape memory thermosets

n this work, a new family of poly(thiourethane) shape memory thermosetting actuators was developed and characterized. These materials can be easily prepared from mixtures of two different aliphatic diisocyanates and a trithiol in the presence of a latent catalyst, allowing an easy manipulation of the formulation. Rheological studies of the curing process confirm the latent character of the formulations. The glass transition temperatures and the mechanical properties can be modified by varying the proportion of diisocyanates (hexamethylene diisocyanate, HDI, and isophorone diisocyanate, IPDI) with stoichiometric amounts of trimethylolpropane tris(3-mercaptopropionate). The shape-memory behavior was deeply investigated under three different conditions: unconstrained, partially constrained, and fully constrained. Tests were performed in single cantilever bending mode to simulate conditions closer to real complex mechanics of thermomechanical actuators under flexural performances. The complex recovery process in single cantilever bending mode was compared with that obtained using tensile mode. The results evidenced that the amount of recovery force in fully constrained conditions, or energy released during the recovery process in partially constrained, can be modulated by simply changing the proportion of both diisocyanates. A simple model based on Timoshenko beam theory was used for the prediction of the amount of work performed. The reported results are an important guideline to design shape-memory materials based on poly(thiourethane) networks, establishing criteria for the choice of the material depending on the expected applicationPeer ReviewedPostprint (author's final draft