The endoribonucleolytic N-terminal half of Escherichia coli RNase E is evolutionarily conserved in Synechocystis sp. and other bacteria but not the C-terminal half, which is sufficient for degradosome assembly

Escherichia coli RNase E, an essential single-stranded specific endoribonuclease, is required for both ribosomal RNA processing and the rapid degradation of mRNA. The availability of the complete sequences of a number of bacterial genomes prompted us to assess the evolutionarily conservation of bacterial RNase E. We show here that the sequence of the N-terminal endoribonucleolytic domain of RNase E is evolutionarily conserved in Synechocystis sp. and other bacteria. Furthermore, we demonstrate that the Synechocystis sp. homologue binds RNase E substrates and cleaves them at the same position as the E. coli enzyme. Taken together these results suggest that RNase E-mediated mechanisms of RNA decay are not confined to E. coli and its close relatives. We also show that the C-terminal half of E. coli RNase E is both sufficient and necessary for its physical interaction with the 3'-5' exoribonuclease polynucleotide phosphorylase, the RhlB helicase, and the glycolytic enzyme enolase, which are components of a "degradosome" complex. Interestingly, however, the sequence of the C-terminal half of E. coli RNase E is not highly conserved evolutionarily, suggesting diversity of RNase E interactions with other RNA decay components in different organisms. This notion is supported by our finding that the Synechocystis sp. RNase E homologue does not function as a platform for assembly of E. coli degradosome components

Bose-Einstein condensation of excitons in Cu2_2O

We present a parameter-free model which estimates the density of excitons in Cu$_2$O, related to experiments that have tried to create an excitonic Bose-Einstein condensate. Our study demonstrates that the triplet-state excitons move along adiabats and obey classical statistics, while the singlet-state excitons are a possible candidate for forming a Bose-Einstein condensate. Finally we show that the results of this study do not change qualitatively in a two-dimensional exciton gas, which can be realized in a quantum well.Comment: 6 pages, RevTex, 1 ps figur

Evolution and instabilities of disks harboring super massive black holes

The bar formation is still an open problem in modern astrophysics. In this paper we present numerical simulation performed with the aim of analyzing the growth of the bar instability inside stellar-gaseous disks, where the star formation is triggered, and a central black hole is present. The aim of this paper is to point out the impact of such a central massive black hole on the growth of the bar. We use N-body-SPH simulations of the same isolated disk-to-halo mass systems harboring black holes with different initial masses and different energy feedback on the surrounding gas. We compare the results of these simulations with the one of the same disk without black hole in its center. We make the same comparison (disk with and without black hole) for a stellar disk in a fully cosmological scenario. A stellar bar, lasting 10 Gyrs, is present in all our simulations. The central black hole mass has in general a mild effect on the ellipticity of the bar but it is never able to destroy it. The black holes grow in different way according their initial mass and their feedback efficiency, the final values of the velocity dispersions and of the black hole masses are near to the phenomenological constraints.Comment: 10 pages, 8 figures, accepted for pubblication in "Astrophysics and Space Science

The black-hole masses of Seyfert galaxies and quasars

The central black-hole masses of a sample of 30 luminous quasars are estimated using H-beta FWHM measurements from a combination of new and previously-published nuclear spectra. The quasar black-hole mass estimates are combined with reverberation-mapping measurements for a sample of Seyfert galaxies (Wandel 1999) in order to study AGN black-hole masses over a wide range in nuclear luminosity. It is found that black-hole mass and bulge luminosity are well correlated and follow a relation consistent with that expected if black-hole and bulge mass are directly proportional. Contrary to the results of Wandel (1999) no evidence is found that Seyfert galaxies follow a different Mblack-Mbulge relation to quasars. However, the black-hole mass distributions of the radio-loud and radio-quiet quasar sub-samples are found to be significantly different, with the median black-hole mass of the radio-loud quasars a factor of three larger than their radio-quiet counterparts. Finally, utilizing the elliptical galaxy fundamental plane to provide stellar velocity dispersion estimates, a comparison is performed between the virial H-beta black-hole mass estimates and those of the Mblack-sigma correlations of Gebhardt et al. (2000a) and Merritt & Ferrarese (2000). With the disc-like geometry of the broad-line region adopted in this paper, the virial H-beta black-hole masses indicate that the correct normalization of the black-hole vs. bulge mass relation is Mblack=0.0025Mbulge, while the standard assumption of purely random broad-line velocities leads to Mblack=0.0008Mbulge. The normalization of Mblack=0.0025Mbulge provided by the disc model is in remarkably good agreement with that inferred for our quasar sample using the (completely independent) Mblack-sigma correlations.Comment: 10 pages, 6 figures, accepted for publication in MNRA

A Supersymmetric D4 Model for mu-tau Symmetry

We construct a supersymmeterized version of the model presented by Grimus and Lavoura (GL) in [1] which predicts theta_{23} maximal and theta_{13}=0 in the lepton sector. For this purpose, we extend the flavor group, which is D4 x Z2^{(aux)} in the original model, to D4 x Z5. An additional difference is the absence of right-handed neutrinos. Despite these changes the model is the same as the GL model, since theta_{23} maximal and theta_{13}=0 arise through the same mismatch of D4 subgroups, D2 in the charged lepton and Z2 in the neutrino sector. In our setup D4 is solely broken by gauge singlets, the flavons. We show that their vacuum structure, which leads to the prediction of theta_{13} and theta_{23}, is a natural result of the scalar potential. We find that the neutrino mass matrix only allows for inverted hierarchy, if we assume a certain form of spontaneous CP violation. The quantity |m_{ee}|, measured in neutrinoless double beta decay, is nearly equal to the lightest neutrino mass m3. The Majorana phases phi1 and phi2 are restricted to a certain range for m3 < 0.06 eV. We discuss the next-to-leading order corrections which give rise to shifts in the vacuum expectation values of the flavons. These induce deviations from maximal atmospheric mixing and vanishing theta_{13}. It turns out that these deviations are smaller for theta_{23} than for theta_{13}.Comment: 19 pages, 4 figure

Diet quality, stress and common mental health problems: A cohort study of 121,008 adults

Background & aims Overall diet quality may partially mediate the detrimental effects of stress and neuroticism on common mental health problems: stressed and/or neurotic individuals may be more prone to unhealthy dietary habits, which in turn may contribute to depression and anxiety. Lifestyle interventions for depressed, anxious or at-risk individuals hinge on this idea, but evidence to support such pathway is missing. Here, we aim to prospectively evaluate the role of overall diet quality in common pathways to developing depression and anxiety. Methods At baseline, N = 121,008 individuals from the general population (age 18–93) completed an extensive food frequency questionnaire, based on which overall diet quality was estimated. Participants also reported on two established risk factors for mental health problems, i.e. past-year stress exposure (long-term difficulties, stressful life-events) and four neuroticism traits (anger-hostility, self-consciousness, impulsivity, vulnerability). Depression and anxiety were assessed at baseline and follow-up (n = 65,342, +3.6 years). Overall diet quality was modeled as a mediator in logistic regression models predicting the development of depression and anxiety from common risk factors. Results High stress and high neuroticism scores were - albeit weakly - associated with poorer diet quality. Poor diet quality, in turn, did not predict mental health problems. Overall diet quality did not mediate the relationship between stress/neuroticism and common mental health problems: effects of stress, neuroticism and stress-by-neuroticism interactions on mental health problems at follow-up consisted entirely of direct effects (98.6%–100%). Conclusions Diet quality plays no mediating role in two established pathways to common mental health problems. As overall diet quality was reduced in stressed and neurotic individuals, these groups may benefit from dietary interventions. However, such interventions are unlikely to prevent the onset or recurrence of depression and anxiety.publishedVersio

quasiharmonic equations of state for dynamically-stabilized soft-mode materials

We introduce a method for treating soft modes within the analytical framework of the quasiharmonic equation of state. The corresponding double-well energy-displacement relation is fitted to a functional form that is harmonic in both the low- and high-energy limits. Using density-functional calculations and statistical physics, we apply the quasiharmonic methodology to solid periclase. We predict the existence of a B1--B2 phase transition at high pressures and temperatures

Graph Invariants of Vassiliev Type and Application to 4D Quantum Gravity

We consider a special class of Kauffman's graph invariants of rigid vertex isotopy (graph invariants of Vassiliev type). They are given by a functor from a category of colored and oriented graphs embedded into a 3-space to a category of representations of the quasi-triangular ribbon Hopf algebra $U_q(sl(2,\bf C))$. Coefficients in expansions of them with respect to $x$ ($q=e^x$) are known as the Vassiliev invariants of finite type. In the present paper, we construct two types of tangle operators of vertices. One of them corresponds to a Casimir operator insertion at a transverse double point of Wilson loops. This paper proposes a non-perturbative generalization of Kauffman's recent result based on a perturbative analysis of the Chern-Simons quantum field theory. As a result, a quantum group analog of Penrose's spin network is established taking into account of the orientation. We also deal with the 4-dimensional canonical quantum gravity of Ashtekar. It is verified that the graph invariants of Vassiliev type are compatible with constraints of the quantum gravity in the loop space representation of Rovelli and Smolin.Comment: 34 pages, AMS-LaTeX, no figures,The proof of thm.5.1 has been improve