Testing for hysteresis in unemployment in OECD countries. New evidence using stationarity panel tests with breaks

This paper tests hysteresis effects in unemployment using panel data for 19 OECD countries covering the period 1956-2001. The tests exploit the cross-section variations of the series, and additionally, allow for a different number of endogenous breakpoints in the unemployment series. The critical values are simulated based on our specic panel sizes and time periods. The ndings stress the importance of accounting for exogenous shocks in the series and give support to the natural-rate hypothesis of unemployment for the majority of the countries analyzed.structural breaks, panel unit root tests, hysteresis

New evidence of the real interest rate parity for OECD countries using panel unit root tests with breaks

This paper tests for real interest parity (RIRP) among the nineteen major OECD countries over the period 1978:Q2-1998:Q4. The econometric methods applied consist of combining the use of several unit root or stationarity tests designed for panels valid under cross-section dependence and presence of multiple structural breaks. Our results strongly support the fulfilment of the weak version of the RIRP for the studied period once dependence and structural breaks are accounted for.structural breaks, economic integration, unit root tests, cross-section dependence, real interest rate parity, panel data

Disentangling α and β relaxation in orientationally disordered crystals with theory and experiments.

We use a microscopically motivated generalized Langevin equation (GLE) approach to link the vibrational density of states (VDOS) to the dielectric response of orientational glasses (OGs). The dielectric function calculated based on the GLE is compared with experimental data for the paradigmatic case of two OGs: freon-112 and freon-113, around and just above T_{g}. The memory function is related to the integral of the VDOS times a spectral coupling function γ(ω_{p}), which tells the degree of dynamical coupling between molecular degrees of freedom at different eigenfrequencies. The comparative analysis of the two freons reveals that the appearance of a secondary β relaxation in freon-112 is due to cooperative dynamical coupling in the regime of mesoscopic motions caused by stronger anharmonicity (absent in freon-113) and is associated with the comparatively lower boson peak in the VDOS. The proposed framework brings together all the key aspects of glassy physics (VDOS with the boson peak, dynamical heterogeneity, dissipation, and anharmonicity) into a single model

Deducing high pressure behavior for chemically fragile systems: the polymorphism of spironolactone

International audienc

Reversible and irreversible colossal barocaloric effects in plastic crystals

The extremely large latent heat exchanged in phase transitions involving strong molecular orientational disordering has recently led to the proposal of plastic crystals as a feasible solution for solid-state barocaloric eco-friendly cooling technologies. Here we determine the reversible barocaloric response of four plastic crystals derived from neopentane [C(CH3)4]: (NH2)C(CH2OH)3 (TRIS for short), (NH2)(CH3)C(CH2OH)2 (AMP), (CH3)C(CH2OH)3 (PG) and (CH3)3C(CH2OH) (NPA). All of them display colossal entropy changes at their ordered-plastic phase transition, which is a primal requirement for competitive barocaloric materials. However, we show that it is also important to verify that the large barocaloric effects can be achieved using pressures that, while being moderate, are large enough to overcome the pressure-dependent hysteresis. From this quantity and using the quasi-direct method, we determine the minimum pressure needed to achieve reversible barocaloric effects, prev, for each compound. Specifically, we find a small and moderate prev for PG and NPA, respectively, which therefore display colossal reversible barocaloric effects comparable to harmful fluids used in current refrigerators and thus confirm the potential of plastic crystals as excellent alternatives. Instead, in TRIS and AMP, the obtained prev is excessive to yield reversible barocaloric effects useful for cyclic applications.This work was supported by the MINECO projects MAT2016-75823-R and FIS2017-82625-P, the DGU project 2017SGR-42, the UK EPSRC grant EP/M003752/1, and the ERC Starting grant no. 680032. X. M. is grateful for support from the Royal Society

Nose temperature and anticorrelation between recrystallization kinetics and molecular relaxation dynamics in amorphous morniflumate at high pressure

We probe the dielectric response of the supercooled liquid phase of Morniflumate, a drug with anti-inflammatory and antipyretic properties, studying in particular the pressure and temperature dependence of the relaxation dynamics, glass transition temperature Tg, and recrystallization kinetics. Tg increases by roughly 20 K every 100 MPa at low applied pressure, where the ratio Tg/Tm has a constant value of ~0.8 (Tm = melting point). Liquid Morniflumate displays two dielectric relaxations: the structural a relaxation associated with the collective reorientational motions, which become arrested at Tg, and a secondary relaxation likely corresponding to an intramolecular dynamics. The relaxation times of both processes scale approximately with the inverse reduced temperature Tg/T. Near room temperature and under an applied pressure of 50 MPa, supercooled Morniflumate recrystallizes in a characteristic time of few hours, with an Avrami exponent of 1.15. Under these conditions, the recrystallization rate is a nonmonotonic function of temperature, displaying a maximum at around 298 K, which can be taken to be the optimum crystal growth temperature Tnose. The ß relaxation becomes kinetically frozen at ambient temperature under an applied hydrostatic pressure higher than 320 MPa, suggesting that the Morniflumate glass should be kinetically stable under these conditions.Peer ReviewedPostprint (author's final draft

Tuning the Kinetic Stability of the Amorphous Phase of the Chloramphenicol Antibiotic

We employ broadband dielectric spectroscopy to study the relaxation dynamics and crystallization kinetics of a broad-spectrum antibiotic, chloramphenicol, in its supercooled liquid form. Two dynamic processes are observed: the structural a relaxation, which becomes kinetically frozen at Tg = 302 ± 1 K, and an intramolecular secondary relaxation. Under isothermal conditions, the supercooled drug displays interconversion between different isomers, followed by recrystallization. Recrystallization follows the Avrami law with Avrami exponent n = 1.3 ± 0.1, consistent with a one dimensional growth of crystalline platelets, as observed by electron microscopy. Exposure to humid atmosphere and subsequent heating to high temperature is found to degrade the compound. The partially degraded sample displays a much lower tendency to crystallize, likely because the presence of the degradation products results in spatial frustration. This sample exhibits enhanced conductivity and an additional relaxation, intermediate to the ones observed in the pure sample, which likely corresponds to the noncooperative dynamics of the main degradation product. We find that dispersing the antibiotic in polylactic acid results in an amorphous sample which does not crystallize at room temperature for relatively long times.Peer ReviewedPostprint (published version

Stability Hierarchy between Piracetam Forms I, II, and III from Experimental Pressure-Temperature Diagrams and Topological Inferences

International audienceThe trimorphism of the active pharmaceutical ingredient piracetam is a famous case of polymorphism that has been frequently revisited by many researchers. The phase relationships between forms I, II, and III were ambiguous because they seemed to depend on the heating rate of the DSC and on the history of the samples or they have not been observed at all (equilibrium II-III). In the present paper, piezo-thermal analysis and high-pressure differential thermal analysis have been used to elucidate the positions of the different solid-solid and solid-liquid equilibria. The phase diagram, involving the three solid phases, the liquid phase and the vapor phase, has been constructed. It has been shown that form III is the high-pressure, low-temperature form and the stable form at room temperature. Form II is stable under intermediary conditions and form I is the low pressure, high temperature form, which possesses a stable melting point. The present paper demonstrates the strength of the topological approach based on the Clapeyron equation and the alternation rule when combined with high-pressure measurement