Astrophysics: quark matter in compact stars?

In a theoretical interpretation of observational data from the neutron star EXO 0748-676, Ozel concludes that quark matter probably does not exist in the centre of neutron stars. However, this conclusion is based on a limited set of possible equations of state for quark matter. Here we compare Ozel's observational limits with predictions based on a more comprehensive set of proposed quark-matter equations of state from the literature, and conclude that the presence of quark matter in EXO 0748-676 is not ruled out.

Symmetry energy of dilute warm nuclear matter.

The symmetry energy of nuclear matter is a fundamental ingredient in the investigation of exotic nuclei, heavy-ion collisions, and astrophysical phenomena. New data from heavy-ion collisions can be used to extract the free symmetry energy and the internal symmetry energy at subsaturation densities and temperatures below 10 MeV. Conventional theoretical calculations of the symmetry energy based on mean-field approaches fail to give the correct low-temperature, low-density limit that is governed by correlations, in particular, by the appearance of bound states. A recently developed quantum-statistical approach that takes the formation of clusters into account predicts symmetry energies that are in very good agreement with the experimental data. A consistent description of the symmetry energy is given that joins the correct low-density limit with quasiparticle approaches valid near the saturation density.

Co-existing structures of an mRNA stability determinant. The 5' region of the Escherichia coli and Serratia marcescens ompA mRNA.

The structure of untranslated regions of mRNA is thought to play a key role in the degradation of mRNAs by specific RNases. As a model system, in vitro transcripts of the stability determining 5' non-coding region of bacterial ompA mRNA were investigated by calculation of secondary structure models and by experiments applying the temperature-gradient gel electrophoresis (TGGE). For the theoretical prediction of secondary structures an algorithm was used, which yields the structure of lowest free energy as well as a large set of suboptimal structures. Three structures were predicted to co-exist in similar concentrations under native conditions. They denature in a low temperature transition leading to a unique structure which denatures in a high temperature transition. The prediction of three structures and two transitions could be confirmed experimentally by TGGE. Due to the use of transcripts of different length the conformational transitions could be attributed to distinct parts of the molecules. A pseudoknot structural motif was predicted theoretically, but could not be confirmed experimentally. Comparing ompA transcripts of E. coli and S. marcescens, a conservation of structural features could be shown in spite of a sequence homology of only 63%. Regarding the sequential folding of the transcript after synthesis, a metastable structure is formed first and is converted slowly into structures of lower free energy. The biological implications for in vivo degradation are discussed.

Association between alcohol consumption and carotid intima-media thickness in a healthy population: data of the STRATEGY study (Stress, Atherosclerosis and ECG Study).

BACKGROUND/OBJECTIVES: Epidemiological evidence suggests a protective effect of moderate alcohol consumption on cardiovascular events. However, studies assessing the association between alcohol intake and intima-media thickness (IMT) as a marker of subclinical atherosclerosis have provided inconsistent results. The aim of this analysis of the Stress Atherosclerosis and ECG Study (STRATEGY study) was to investigate the relation between alcohol intake and IMT in a selectively healthy population. SUBJECTS/METHODS: In a cross-sectional study, laboratory values, anthropometric data, nutrition habits and physical activity were assessed in 106 men and 107 women, evenly distributed between 30 and 70 years. Carotid IMT was determined by B-mode ultrasonography according to the standardized protocol of the Study of Health in Pomerania. RESULTS: In men, a significant positive correlation between daily alcohol consumption and IMT was observed (P<0.0001), whereas in women the positive correlation was not significant. The type of beverage consumed did not affect this finding. The mean IMT was significantly higher in men with an alcohol intake above the upper limit of 20 g/day than in men with an alcohol intake <20 g/day (P<0.001). According to a stepwise linear regression model adjusted for age, conventional risk factors, nutrition and physical activity, the IMT increases by 0.0253 mm per 21.4 g/day intake of alcohol in men (P<0.05). CONCLUSIONS: The STRATEGY study revealed a positive association between alcohol consumption and carotid IMT in healthy men aged 30-70 years. This relationship remained significant after adjustment for nutrition, physical activity, anthropometry and conventional cardiovascular risk factors.