New Class of Compact Stars at High Density

We discuss the equation of state for cold, dense quark matter in perturbation theory, and how it might match onto that of hadronic matter. Certain choices of the renormalization scale correspond to a strongly first order chiral transition, and may generate a new class of small and very dense quark stars. The results for the mass-radius relation are compatible with the recent determination of the mass and the radius of an isolated neutron star by Pons et al.Comment: Latex, 7 pages, 4 figures. Presented at the International Conference on Statistical QCD, Bielefeld, Germany, 26-30 August 2001. Requires espcrc1.st

The sdA problem - II. Photometric and Spectroscopic Follow-up

Subdwarf A star (sdA) is a spectral classification given to objects showing H-rich spectra and sub-main sequence surface gravities, but effective temperature lower than the zero-age horizontal branch. Their evolutionary origin is an enigma. In this work, we discuss the results of follow-up observations of selected sdAs. We obtained time resolved spectroscopy for 24 objects, and time-series photometry for another 19 objects. For two targets, we report both spectroscopy and photometry observations. We confirm seven objects to be new extremely-low mass white dwarfs (ELMs), one of which is a known eclipsing star. We also find the eighth member of the pulsating ELM class.Comment: Accepted for publication in MNRAS. 19 pages, 30 figures, 6 table

Nucleation of quark matter in protoneutron star matter

The phase transition from hadronic to quark matter may take place already during the early post-bounce stage of core collapse supernovae when matter is still hot and lepton rich. If the phase transition is of first order and exhibits a barrier, the formation of the new phase occurs via the nucleation of droplets. We investigate the thermal nucleation of a quark phase in supernova matter and calculate its rate for a wide range of physical parameters. We show that the formation of the first droplet of a quark phase might be very fast and therefore the phase transition to quark matter could play an important role in the mechanism and dynamics of supernova explosions.Comment: v3: fits version published in Physical Review

Asteroseismological study of massive ZZ Ceti stars with fully evolutionary models

We present the first asteroseismological study for 42 massive ZZ Ceti stars based on a large set of fully evolutionary carbon$-$oxygen core DA white dwarf models characterized by a detailed and consistent chemical inner profile for the core and the envelope. Our sample comprise all the ZZ Ceti stars with spectroscopic stellar masses between 0.72 and $1.05M_{\odot}$ known to date. The asteroseismological analysis of a set of 42 stars gives the possibility to study the ensemble properties of the massive pulsating white dwarf stars with carbon$-$oxygen cores, in particular the thickness of the hydrogen envelope and the stellar mass. A significant fraction of stars in our sample have stellar mass high enough as to crystallize at the effective temperatures of the ZZ Ceti instability strip, which enables us to study the effects of crystallization on the pulsation properties of these stars. Our results show that the phase diagram presented in Horowitz et al. (2010) seems to be a good representation of the crystallization process inside white dwarf stars, in agreement with the results from white dwarf luminosity function in globular clusters.Comment: 58 pages, 11 figures, accepted in Ap

Remarks on transient photon production in heavy ion collisions

In this note, we discuss the derivation of a formula that has been used in the literature in order to compute the number of photons emitted by a hot or dense system during a finite time. Our derivation is based on a variation of the standard operator-based $S$-matrix approach. The shortcomings of this formula are then emphasized, which leads to a negative conclusion concerning the possibility of using it to predict transient effects for the photon rate.Comment: 13 page

Does interview setting influence disclosure of violence? A study in elderly

Background: violence is a very sensitive research topic and interview's setting might influence the participation rate and response accuracy. We aimed to evaluate such effect when assessing the prevalence of different types of violence in a sample of urban elderly by comparing those interviewed at home with those assessed at the research office. Methods: study subjects were members of a cohort of urban dwellers previously assembled using random digit dialling. The initial 450 individuals aged 60-84 years old were invited to participate in the present study, after being randomly allocated into two groups: 150 for being scheduled to research office interview and 300 to home interview. Both groups allocated were similar regarding gender, age, education, marital status and behavioural characteristics such as smoking and drinking alcohol. Information was obtained by face-to-face standardised interviews. Results: we obtained a participation rate of 67.0% in the group allocated to home interview and 70.7% in the other group (P = 0.431). No statistically significant differences were found when prevalence of violence during the previous year was compared according to the interview setting (physical 2.5 versus 1.0%, psychological 19.7 versus 19.0%, financial mistreatment 8.6 versus 9.5%, sexual 1.0 versus 1.0% and neglect 5.1 versus 3.8% in home and research office, respectively). Conclusion: our results indicate that the interview setting has no influence both in participation rate and in the prevalence estimates of different types of violence in the elderly. © The Author 2011. Published by Oxford University Press on behalf of the British Geriatrics Society. All rights reserved.The European project ‘Elder Abuse: A multinational prevalence survey (Project A/100929)’ was supported by the Executive Agency for Health and Consumers.. We would like to thank to the ABUEL Group: Elli Loannidi (Greece), Francisco Torres-Gonzalez (Spain), Giovanni Lamura (Italy), Joaquim Soares (Sweden), Jutta Lindert (Germany), Mindaugas Stankunas (Lithuania). Sílvia Fraga (SFRH/BD/44408/2008) and Diogo Costa (SFRH/BD/66388/2009) have a PhD grant from Fundação para a Ciência e a Tecnologia

NMR evidence for very slow carrier density fluctuations in the organic metal (TMTSF)2_2ClO4_4

We have investigated the origin of the large increase in spin-echo decay rates for the $^{77}$Se nuclear spins at temperatures near to $T=30K$ in the organic superconductor (TMTSF)$_2$ClO$_4$. The measured angular dependence of $T_2^{-1}$ demonstrates that the source of the spin-echo decays lies with carrier density fluctuations rather than fluctuations in TMTSF molecular orientation. The very long time scales are directly associated with the dynamics of the anion ordering occurring at $T=25K$, and the inhomogeneously broadened spectra at lower temperatures result from finite domain sizes. Our results are similar to observations of line-broadening effects associated with charge-ordering transitions in quasi-two dimensional organic conductors.Comment: 5 pages, 4 figure