Equation of state of metallic hydrogen from Coupled Electron-Ion Monte Carlo simulations

We present a study of hydrogen at pressures higher than molecular dissociation using the Coupled Electron-Ion Monte Carlo method. These calculations use the accurate Reptation Quantum Monte Carlo method to estimate the electronic energy and pressure while doing a Monte Carlo simulation of the protons. In addition to presenting simulation results for the equation of state over a large region of phase space, we report the free energy obtained by thermodynamic integration. We find very good agreement with DFT calculations for pressures beyond 600 GPa and densities above $\rho=1.4 g/cm^3$. Both thermodynamic as well as structural properties are accurately reproduced by DFT calculations. This agreement gives a strong support to the different approximations employed in DFT, specifically the approximate exchange-correlation potential and the use of pseudopotentials for the range of densities considered. We find disagreement with chemical models, which suggests a reinvestigation of planetary models, previously constructed using the Saumon-Chabrier-Van Horn equations of state.Comment: 9 pages, 7 figure

Born-Oppenheimer and Renner-Teller coupled-channel quantum reaction dynamics of O(3P) + H2+(X2Σg+) collisions

We present Born-Oppenheimer (BO) and Renner-Teller (RT) time dependent quantum dynamics studies of the reactions O(3P) + H2+(X2Σg+) → OH+(X3Σ-) + H(2S) and OH(X2Π) + H+. We consider the OH2+ X˜2A″ and Ã2A′ electronic states that correlate with a linear 2Π species. The electronic angular momenta operators L and L2 are considered in nonadiabatic coupled-channel calculations, where the associated RT effects are due to diagonal VRT potentials that add up to the PESs and to off-diagonal CRTcouplings between the potential energy surfaces (PESs). Initial-state-resolved reaction probabilities PI, integral cross sections σI, and rate constants kI are obtained using recent ab initio PESs and couplings and the real wavepacket formalism. Because the PESs are strongly attractive, PI have no threshold energy and are large, σI decrease with collision energy, and kI depend little on the temperature. The X˜2A″ PES is up to three times more reactive than the Ã2A′ PES and H2+ rotational effects (j0 = 0, 1) are negligible. The diagonal VRT potentials are strongly repulsive at the collinearity and nearly halve all low-energy observables with respect to the BO ones. The off-diagonal CRTcouplings are important at low partial waves, where they mix the X˜2A″ and Ã2A′ states up to ∼20%. However, VRT effects predominate over the CRT ones that change at most by ∼19% the BO values of σI and kI. The reaction O(3P) + H2+(X2Σg+) → OH+(X3Σ-) + H(2S) is probably one of the most reactive atom + diatom collisions because its RT rate constant at room temperature is equal to 2.26 × 10-10 cm3 s-1. Within the BO approximation, the present results agree rather well with recent quasiclassical and centrifugal-sudden data using the sa me PESsThis work was supported by the Spanish Ministry of Science and Innovation (MICINN projects CTQ2011-27857-C02-01 and CONSOLIDER INGENIO 2010 under grant no. CSD2009-00038 entitled ‘‘Molecular Astrophysics: the Herschel and Alma era’’). Thanks are also given to the ‘‘Generalitat de Catalunya’’ (Autonomous Government of Catalonia; refs. 2014SGR 25, 2014SGR 1582 and XRQTC) for some help. We gratefully acknowledge H. Guo and D. Xie for the matrix elements of the electronic angular moment

Analysis of Dangerous Sea States in the Northwestern Mediterranean Area

Extreme sea waves, although rare, can be notably dangerous when associated with energetic sea states and can generate risks for the navigation. In the last few years, they have been the object of extensive research from the scientific community that helped with understanding the main physical aspects; however, the estimate of extreme waves probability in operational forecasts is still debated. In this study, we analyzed a number of sea-states that occurred in a precise area of the Mediterranean sea, near the location of a reported accident, with the objective of relating the probability of extreme events with different sea state conditions. For this purpose, we performed phase-resolving simulations of wave spectra obtained from a WaveWatch III hindcast, using a Higher Order Spectral Method. We produced statistics of the sea-surface elevation field, calculating crest distributions and the probability of extreme events from the analysis of a long time-series of the surface elevation. We found a good matching between the distributions of the numerically simulated field and theory, namely Tayfun second- and third- order ones, in contrast with a significant underestimate given by the Rayleigh distribution. We then related spectral quantities like angular spreading and wave steepness to the probability of occurrence of extreme events finding an enhanced probability for high mean steepness seas and narrow spectra, in accordance with literature results, finding also that the case study of the reported accident was not amongst the most dangerous. Finally, we related the skewness and kurtosis of the surface elevation to the wave steepness to explain the discrepancy between theoretical and numerical distributions

SYNTHESIS OF STELLAR Mg AND Fe ABSORPTION INDICES FOR STELLAR POPULATION STUDIES. II. THE EXTENDED AND UP-TO-DATE COLLECTION

This paper is mainly concerned with the prediction of absorption-line spectral features in cool stars, to be used as input in stellar population synthesis projects. From a detailed comparison with the solar intensity spectrum, we have re-ned the main parameters of atomic and molecular absorption lines that are prominent in the 4850E5400 wavelength interval. This line list was used to compute an extensive Ae library of synthetic stellar spectra at high resolution in the temperature range K, T eff \ 4000E8000 surface gravity interval log g \ 1.0E5.0 dex, metallicities ((M/H)) from (1.0 to )0.5 dex, and micro- turbulent velocity m \ 2k m s~1. The computations were performed by using the latest release of KuruczIs model atmospheres and numerical codes. The library contains a total of 693 synthetic spectra, from which iron and magnesium indices were obtained, together with the corresponding "" pseudocontinuum II Nuxes. We illustrate the behavior of -ve "" Lick-like II spectral indices, namely, Mg b, Fe5270, and Mg 1 ,M g 2 , Fe5335, in terms of the main atmospheric parameters, namely, e†ective temperature, surface gravity, and metallicity. The trend of the indices with microturbulent velocity is also illustrated by means of an addi- tional set of spectra computed at di†erent microturbulent velocities. Transformation equations of the theoretical grid into the Lick/IDS observational database are presented, showing the full consistency of our grid with the empirical database. Subject heading: galaxies: stellar content E stars: atmospheres E stars: late-typ

Torus quantum vortex knots in the Gross-Pitaevskii model for Bose-Einstein condensates

We examine the static and dynamic properties of quantum knots in a Bose-Einstein condensate. In particular, we consider the Gross-Pitaevskii model and revise a technique to construct ab initio the condensate wave-function of a generic torus knot. After analysing its excitation energy, we study its dynamics, relating the topological parameter to its translational velocity and characteristic size. We also investigate the breaking mechanisms of non shape-preserving torus knots, confirming an evidence of universal decaying behaviour previously observed