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We study the expansion history of the universe up to a redshift of z=1.75 using the 194 recently published SnIa data by Tonry et. al. and Barris et. al. In particular we find the best fit forms of several cosmological models and $H(z)$ ansatze, determine the best fit values of their parameters and rank them according to increasing value of $\chi_{min}^2$ (the minimum value of $\chi^2$ for each $H(z)$ ansatz). We use a prior of $\Omega_{0m} = 0.3$ and assume flat geometry of the universe. No prior assumptions are made about validity of energy conditions. The fitted models are fourteen and include SCDM, LCDM, dark energy with constant equation of state parameter $w$ (quiessence), third order polynomial for $H(1+z)$, Chaplygin gas, Cardassian model, $w(z)=w_0 + w_1 z$, $w(z)=w_0 + z w_1/(1+z)$, an oscillating ansatz for $H(z)$ etc. All these models with the exception of SCDM are consistent with the present data. However, the quality of the fit differs significantly among them and so do the predicted forms of $w(z)$ and $H(z)$ at best fit. The worst fit among the data-consistent models considered corresponds to the simplest model LCDM ($\chi_{min}^2 = 198.7$ for $\Omega_{0m} = 0.34$) while the best fit is achieved by the three parameter oscillating ansatz ($\chi_{min}^2 = 194.1$). Most of the best fit ansatze have an equation of state parameter $w(z)$ that varies between $w(z) \simeq -1$ for $z 0$ for $z>1$. This implies that the sign of the pressure of the dark energy may be alternating as the redshift increases. The goodness of fit of the oscillating $H(z)$ ansatz lends further support to this possibility., Comment: 10 two column pages, 4 figures. The numerical analysis of the paper is available at http://leandros.physics.uoi.gr/cosmofit.htm. An appendix, some references and additional 1\sigma parameter errors have been included

We study analytically and numerically the evolution of bound systems in universes with accelerating expansion where the acceleration either increases with time towards a Big Rip singularity (phantom cosmologies) or decreases with time (quintessence). We confirm the finding of Caldwell et. al. [arXiv:astro-ph/0302506] (hereafter CKW) that bound structures get dissociated in phantom cosmologies but we demonstrate that this happens earlier than anticipated by CKW. In particular we find that the `rip time' when a bound system gets unbounded is not the time when the repulsive phantom energy gravitational potential due to the average $(\rho + 3p)$ balances the attractive gravitational potential of the mass M of the system. Instead, the `rip time' is the time when the minimum of the time dependent effective potential (including the centrifugal term) disappears. For the Milky Way galaxy this happens approximately 180Myrs before the Big Rip singularity instead of approximately 60Myrs indicated by CKW for a phantom cosmology with w=-1.5. A numerical reconstruction of the dissociating bound orbits is presented., Comment: Minor modifications: A table and new references added. The mathematica file for the numerical analysis of the paper is available at http://leandros.physics.uoi.gr/bigrip.htm

The symmetry energy for nuclear matter and its relation to the neutron skin in finite nuclei is discussed. The symmetry energy as a function of density obtained in a self-consistent Green function approach is presented and compared to the results of other recent theoretical approaches. A partial explanation of the linear relation between the symmetry energy and the neutron skin is proposed. The potential of several experimental methods to extract the neutron skin is examined., to appear in Phys. Rev. C

The low-frequency electrical conductivity of strongly nonideal hydrogen, helium, and xenon plasmas was measured in the megabar range of pressures. The plasmas in question were generated by the method of multiple shock compression in planar and cylindrical geometries, whereby it was possible to reduce effects of irreversible heating and to implement a quasi-isentropic regime. As a result, plasma states at pressures in the megabar range were realized, where the electron concentration could be as high as n(e) approximate to 2 x 10(23) cm(-3), which may correspond to either a degenerate or a Boltzmann plasma characterized by a strong Coulomb (Gamma(D) = 1-10) and a strong interatomic (Gamma(a) = r(a)n(a)(1/3) similar to 1) interaction. A sharp increase (by three to five orders of magnitude) in the electrical conductivity of a strongly nonideal plasma due to pressure-produced ionization was recorded, and theoretical models were invoked to describe this increase. Experimental data available in this region and theoretical models proposed by various authors are analyzed. The possibility of a first-order "phase transition" in a strongly nonideal plasma is indicated. (C) 2003 MAIK "Nauka / Interperiodica".

Validerat; 20101217 (root)

The dynamics of heavy-ion collisions is studied in an energy domain in the vicinity of the Fermi energy, The early history of the collision is analyzed from the theoretical and experimental point of view in which the message conveyed by bremsstrahlung photons and neutral pions is exploited, The Boltzmann-Uehling-Uhlenbeck model and the Dubna Cascade Model, both based on similar principles but each adopting different computation technics, are briefly described and their respective predictions are discussed, In particular the emission pattern of bremsstrahlung photons is discussed. The photon production has been measured in the systems Kr-86+Ni-58 at 60A MeV, Ta-181+Au-197 at 40A MeV and Pb-208+Au-197 at 30A MeV and energy spectra, angular distributions and two-photon correlations have been analyzed. We find that bremsstrahlung photons are emitted from two distinct sources that can be correlated with nuclear-matter density oscillations. The properties of photon emission are discussed in terms of collective properties of nuclear matter. The high energy tail of the photon spectrum is interpreted by pi(0) and Delta decay but predominantly by radiative capture of pions, The pi(0) absorption in the nuclear medium is further analyzed by examining their emission pattern. (C) 1997 Elsevier Science B.V.

We use the SnIa Gold dataset to compare LCDM with 10 representative parametrizations of the recent Hubble expansion history $H(z)$. For the comparison we use two statistical tests; the usual $\chi_{min}^2$ which is insensitive to the parametrization number of parameters, and a statistic we call the p-test which depends on both the value of $\chi_{min}^2$ and the number $n$ of the parametrization parameters. The p-test measures the confidence level to which the parameter values corresponding to LCDM are excluded from the viewpoint of the parametrization tested. For example, for a linear equation of state parametrization $w(z)=w_0 + w_1 z$ the LCDM parameter values ($w_0=-1$, $w_1=0$) are excluded at 75% confidence level. We use a flat prior and $\Omega_{0m}=0.3$. All parametrizations tested are consistent with the Gold dataset at their best fit. According to both statistical tests, the worst fits among the 10 parametrizations, correspond to the Chaplygin gas, the brane world and the Cardassian parametrizations. The best fit is achieved by oscillating parametrizations which can exclude the parameter values corresponding to LCDM at 85% confidence level. Even though this level of significance does not provide a statistically significant exclusion of LCDM (it is less than $2\sigma$) and does not by itself constitute conclusive evidence for oscillations in the cosmological expansion, when combined with similar independent recent evidence for oscillations coming from the CMB and matter power spectra it becomes an issue worth of further investigation., Comment: 10 two column pages, 2 figures, 2 tables. Additional statistical tests applied. Accepted in JCAP (to appear)

We analyze an asteroseismic binary system: KIC 7107778, a non-eclipsing, unresolved target, with solar-like oscillations in both components. We used \emph{Kepler} short cadence time series spanning nearly two years to obtain the power spectrum. Oscillation mode parameters were determined using Bayesian inference and a nested sampling Monte Carlo algorithm with the \texttt{DIAMONDS} package. The power profiles of the two components fully overlap, indicating their close similarity. We modelled the two stars with \texttt{MESA} and calculated oscillation frequencies with \texttt{GYRE}. Stellar fundamental parameters (mass, radius and age) were estimated by grid modelling with atmospheric parameters and the oscillation frequencies of $l=0,2$ modes as constraints. Most $l=1$ mixed modes were identified with models searched using a bisection method. Stellar parameters for the two sub-giant stars are: $M_A=1.42\pm0.06$ $M_{\astrosun}$, $M_B=1.39\pm0.03$ $M_{\astrosun}$, $R_A=2.93\pm0.05$ $R_{\astrosun}$, $R_B=2.76\pm0.04$ $R_{\astrosun}$, $t_A=3.32\pm0.54$ Gyr and $t_B=3.51\pm0.33$ Gyr. The mass difference of the system is $\sim$1\%. The results confirm their simultaneous birth and evolution, as is expected from binary formation. KIC 7107778 comprises almost identical twins, and is the first asteroseismic sub-giant binary to be detected., 13 pages, 8 figures

This paper is concerned with the effect of atomic-shell structure on the cold pressure of highly compressed matter up to 1 Gbar and above. The method is to compare band-structure calculations based on augmented spherical waves with results of the quantum-statistical model. Elements treated explicitly are Li, He, Be, Al, and K. No indication for anomalies due to pressure ionization is found. However, an oscillatory behavior of cold-pressure curves is systematically obtained due to isostructural electronic transitions. They are traced back to pressure-induced band shifts and electron redistribution from bands of low angular momentum (typically s and p waves) to bands of higher angular momentum (typically d and f waves). The shifts are shown to occur generally when squeezing normal matter with extended atoms into highly degenerate matter. The anomalies are particularly pronounced for alkali metals: Strong pressure flattening is found for Li at fivefold compression and 5--10 Mbar, and very sharply for K somewhat below fivefold compression and 500 kbar. The oscillations are much weaker for Be and Al. Metallization of He is obtained at 12.1 g/${\mathrm{cm}}^{3}$ and 110 Mbar. For Be, a structural hcp\ensuremath{\rightarrow}bcc transition at 2 Mbar is predicted.

Solid mixtures of ammonia and water, the so-called ammonia hydrates, are thought to be major components of solar and extra-solar icy planets. We present here a thorough characterization of the recently reported high pressure (P)-temperature (T) phase VII of ammonia monohydrate (AMH) using Raman spectroscopy, X-ray diffraction, and quasi-elastic neutron scattering (QENS) experiments in the ranges 4-10 GPa, 450-600 K. Our results show that AMH-VII exhibits common structural features with the disordered ionico-molecular alloy (DIMA) phase, stable above 7.5 GPa at 300 K: both present a substitutional disorder of water and ammonia over the sites of a body-centered cubic lattice and are partially ionic. The two phases however markedly differ in their hydrogen dynamics, and QENS measurements show that AMH-VII is characterized by free molecular rotations around the lattice positions which are quenched in the DIMA phase. AMH-VII is thus a peculiar crystalline solid in that it combines three types of disorder: substitutional, compositional, and rotational.

A full understanding of the phase behavior of CO2–hydrocarbon mixtures at reservoir conditions is essential for the proper design, construction and operation of carbon capture and storage (CCS) and enhanced oil recovery (EOR) processes. While equilibrium data for binary CO2–hydrocarbon mixtures are plentiful, equilibrium data and validated equations of state having reasonable predictive capability for multi-component CO2–hydrocarbon mixtures are limited. In this work, a new synthetic apparatus was constructed to measure the phase behavior of systems containing CO2 and multicomponent hydrocarbons at reservoir temperatures and pressures. The apparatus consisted of a thermostated variable-volume view cell driven by a computer-controlled servo motor system, and equipped with a sapphire window for visual observation. Two calibrated syringe pumps were used for quantitative fluid injection. The maximum operating pressure and temperature were 40 MPa and 473.15 K, respectively. The apparatus was validated by means of isothermal vapor–liquid equilibrium measurement on (CO2 + heptane), the results of which were found to be in good agreement with literature data. In this work, we report experimental measurements of the phase behavior and density of (CO2 + synthetic crude oil) mixtures. The ‘dead’ oil contained a total of 17 components including alkanes, branched-alkanes, cyclo-alkanes, and aromatics. Solution gas (0.81 methane + 0.13 ethane + 0.06 propane) was added to obtain live synthetic crudes with gas-oil ratios of either 58 or 160. Phase equilibrium and density measurements are reported for the ‘dead’ oil and the two ‘live’ oils under the addition of CO2. The measurements were carried out at temperatures of 298.15, 323.15, 373.15 and 423.15 K and at pressures up to 36 MPa, and included vapor–liquid, liquid–liquid and vapor–liquid–liquid equilibrium conditions. The results are qualitatively similar to published data for mixtures of CO2 with both real crude oils or and simple hydrocarbon mixtures containing both light and heavy components. The present experimental data have been compared with results calculated with two predictive models, PPR78 and PR2SRK, based on the Peng–Robinson 78 (PR78) and Soave–Redlich–Kwong (SRK) equations of state with group-contribution formulae for the binary interaction parameters. Careful attention was paid to the critical constants and acentric factor of high molar-mass components. Since the mixture also contained several light substances with critical temperatures below some or all experimental temperatures, we investigated the use of the Boston–Mathias modification of the PR78 and SRK equations. The results showed that these models can predict with reasonable accuracy the vapor–liquid equilibria of systems containing CO2 and complex hydrocarbon mixtures without the need to regress multiple binary parameters against experimental data.

We study the state of a nanometric helium bubble in bcc-iron as a function of temperature and He content using atomistic calculations. It appears that up to moderate temperatures the Fe lattice can confine He to solid state, in good agreement with known solid-liquid transition diagram of pure He. However, He in the bubble forms an amorphous phase, while an fcc structure is expected at the same temperature and He density. In addition, the He bubble forms a polyhedron whose morphology depends on either the surface energy or the elastic-plastic properties of Fe at either low or high pressure, respectively. Indeed, at high He contents the bubble surface breaks down at the mechanical stability limit of the Fe crystal, leading to a pressure decrease in the bubble.

Electronic states of iron in the lower mantle's dominant mineral, (Mg,Fe,Al)(Fe,Al,Si)O-3 bridgmanite, control physical properties of the mantle including density, elasticity, and electrical and thermal conductivity. However, the determination of electronic states of iron has been controversial, in part due to different interpretations of Mossbauer spectroscopy results used to identify spin state, valence state, and site occupancy of iron. We applied energy-domain Mossbauer spectroscopy to a set of four bridgmanite samples spanning a wide range of compositions: 10-50% Fe/total cations, 0-25% Al/total cations, 12-100% Fe3+/total Fe. Measurements performed in the diamond-anvil cell at pressures up to 76 GPa below and above the high to low spin transition in Fe3+ provide a Mossbauer reference library for bridgmanite and demonstrate the effects of pressure and composition on electronic states of iron. Results indicate that although the spin transition in Fe3+ in the bridgmanite B-site occurs as predicted, it does not strongly affect the observed quadrupole splitting of 1.4 mm/s, and only decreases center shift for this site to 0 mm/s at similar to 70 GPa. Thus center shift can easily distinguish Fe3+ from Fe2+ at high pressure, which exhibits two distinct Mossbauer sites with center shift similar to 1 mm/s and quadrupole splitting 2.4-3.1 and 3.9 mm/s at similar to 70 GPa. Correct quantification of Fe3+/total Fe in bridgmanite is required to constrain the effects of composition and redox states in experimental measurements of seismic properties of bridgmanite. In Fe-rich, mixed-valence bridgmanite at deep-mantle-relevant pressures, up to similar to 20% of the Fe may be a Fe2.5+ charge transfer component, which should enhance electrical and thermal conductivity in Fe-rich heterogeneities at the base of Earth's mantle.

Massive steam and CO2 atmospheres have been proposed for magma ocean outgassing of Earth and terrestrial planets. Yet formation of such atmospheres depends on volatile exchange with the molten interior, governed by volatile solubilities and redox reactions. We determine the evolution of magma ocean–atmosphere systems for a range of oxygen fugacities, C/H ratios, and hydrogen budgets that include redox reactions for hydrogen (H2–H2O), carbon (CO–CO2), methane (CH4), and solubility laws for H2O and CO2. We find that small initial budgets of hydrogen, high C/H ratios, and oxidizing conditions suppress outgassing of hydrogen until the late stage of magma ocean crystallization. Hence, early atmospheres in equilibrium with magma oceans are dominantly carbon-rich, and specifically CO-rich except at the most oxidizing conditions. The high solubility of H2O limits its outgassing to melt fractions below ∼30%, the fraction at which the mantle transitions from vigorous to sluggish convection with melt percolation. Sluggish melt percolation could enable a surface lid to form, trapping water in the interior and thereby maintaining a carbon-rich atmosphere (equilibrium crystallization). Alternatively, efficient crystal settling could maintain a molten surface, promoting a transition to a water-rich atmosphere (fractional crystallization). However, additional processes, including melt trapping and H dissolution in crystallizing minerals, further conspire to limit the extent of H outgassing, even for fractional crystallization. Hence, much of the water delivered to planets during their accretion can be safely harbored in their interiors during the magma ocean stage, particularly at oxidizing conditions., The Planetary Science Journal, 3 (4), ISSN:2632-3338

We establish the complete phase diagram of self-propelled hard disks in two spatial dimensions from the analysis of the equation of state and the statistics of local order parameters. The equilibrium melting scenario is maintained at small activities, with coexistence between active liquid and hexatic order, followed by a proper hexatic phase, and a further transition to an active solid. As activity increases, the emergence of hexatic and solid order is shifted towards higher densities. Above a critical activity and for a certain range of packing fractions, the system undergoes motility-induced phase separation and demixes into low and high density phases; the latter can be either disordered (liquid) or ordered (hexatic or solid) depending on the activity.

The compact binary radio pulsar system J0453+1559 (Martinez et al. 2015) consists of a recycled pulsar as primary component of $1.559(5)\,M_\odot$ and an unseen companion star of $1.174(4)\,M_\odot$. Because of the relatively large orbital eccentricity of $e = 0.1125$, it was argued that the companion is a neutron star, making it the neutron star with the lowest accurately determined mass to date. However, a direct observational determination of the nature of the companion is currently not feasible. Moreover, state-of-the-art stellar evolution and supernova modeling are contradictive concerning the possibility to produce such a low-mass neutron star remnant. Here we challenge the neutron star interpretation by reasoning that the lower-mass component could instead be a white dwarf born in a thermonuclear electron-capture supernova (tECSN) event, in which oxygen-neon deflagration in the degenerate stellar core of an ultra-stripped progenitor ejects several $0.1\,M_\odot$ of matter and leaves a bound ONeFe white dwarf as the second-formed compact remnant. We determine the ejecta mass and remnant kick needed in this scenario to explain the properties of PSR~J0453+1559 by a neutron star--white dwarf system. More work on tECSNe is needed to assess the viability of this scenario., Comment: ApJL, accepted for publication (6 pages, 4 figures)