University of Geneva

About: University of Geneva is a education organization based out in Geneva, Switzerland. It is known for research contribution in the topics: Population & Planet. The organization has 26887 authors who have published 65265 publications receiving 2931373 citations. The organization is also known as: Geneva University & Universite de Geneve.

Stellar evolution with rotation - VIII. Models at $Z$ = 10$^\mathsf{-5}$ and CNO yields for early galactic evolution

Abstract: We calculate a grid of star models with and without the eects of axial rotation for stars in the mass range between 2 and 60 M for the metallicity Z= 10 5 . Star models with initial masses superior or equal to 9 M were computed up to the end of the carbon-burning phase. Star models with masses between 2 and 7 M were evolved beyond the end of the He-burning phase through a few thermal pulses during the AGB phase. Compared to models at Z = 0:02, the low Z models show faster rotating cores and stronger internal-gradients, which favour an important mixing of the chemical elements. The enhancement of N/C at the surface may reach 2 to 3 orders of magnitude for fast rotating stars. Surface enrichments may make the evolved stars less metal poor than they were initially. In very low Z models, primary nitrogen is produced during the He-burning phase by rotational diusion of 12 C into the H-burning shell. A large fraction of the primary 14 N escapes further destruction and enters the envelope of AGB stars, being ejected during the TP-AGB phase and the formation of a planetary nebula. The intermediate mass stars of very lowZ are the main producers of primary 14 N, but massive stars also contribute to this production; no significant primary nitrogen is made in models at metallicity Z= 0:004 or above. We calculate the chemical yields in He, C, N, O and heavy elements and discuss the chemical evolution of the CNO elements at very low Z. Remarkably, the C/ Ov s. O/H diagram is mainly sensitive to the interval of stellar masses, while the N/ Ov s. O/H diagram is mainly sensitive to the average rotation of the stars contributing to the element synthesis. The presently available observations in these diagrams seem to favour contributions either from stars down to about 2 M with normal rotation velocities or from stars above 8 M but with very fast rotation.

Derivation of isotope ratios, errors, and error correlations for U‐Pb geochronology using 205Pb‐235U‐(233U)‐spiked isotope dilution thermal ionization mass spectrometric data

Abstract: A comprehensive treatment of the derivation of U-Pb isotope ratios and their corresponding uncertainties from isotope dilution thermal ionization mass spectrometric measurements is presented. Standard parametric statistical methods of error propagation are utilized to convolve uncertainties associated with instrumental mass fractionation, tracer subtraction, blank Pb and U subtraction, and initial common Pb correction. Derivations include errors and error correlations for total sample U/Pb and Pb isotope ratios (including radiogenic and initial common Pb) for two- and three-dimensional isochron calculations, radiogenic U/Pb and Pb isotope ratios for concordia and radiogenic model age calculations, and the propagation of model age errors from radiogenic isotope ratios.

Brucella abortus transits through the autophagic pathway and replicates in the endoplasmic reticulum of nonprofessional phagocytes

Abstract: Brucella abortus is an intracellular pathogen that replicates within a membrane-bounded compartment. In this study, we have examined the intracellular pathway of the virulent B. abortus strain 2308 (S2308) and the attenuated strain 19 (S19) in HeLa cells. At 10 min after inoculation, both bacterial strains are transiently detected in phagosomes characterized by the presence of early endosomal markers such as the early endosomal antigen 1. At approximately 1 h postinoculation, bacteria are located within a compartment positive for the lysosome-associated membrane proteins (LAMPs) and the endoplasmic reticulum (ER) marker sec61beta but negative for the mannose 6-phosphate receptors and cathepsin D. Interestingly, this compartment is also positive for the autophagosomal marker monodansylcadaverin, suggesting that S2308 and S19 are located in autophagic vacuoles. At 24 h after inoculation, attenuated S19 is degraded in lysosomes, while virulent S2308 multiplies within a LAMP- and cathepsin D-negative but sec61beta- and protein disulfide isomerase-positive compartment. Furthermore, treatment of infected cells with the pore-forming toxin aerolysin from Aeromonas hydrophila causes vacuolation of the bacterial replication compartment. These results are compatible with the hypothesis that pathogenic B. abortus exploits the autophagic machinery of HeLa cells to establish an intracellular niche favorable for its replication within the ER.

The Stueckelberg Field

Abstract: In 1938, Stueckelberg introduced a scalar field which makes an Abelian gauge theory massive but preserves gauge invariance. The Stueckelberg mechanism is the introduction of new fields to reveal a symmetry of a gauge--fixed theory. We first review the Stueckelberg mechanism in the massive Abelian gauge theory. We then extend this idea to the standard model, stueckelberging the hypercharge U(1) and thus giving a mass to the physical photon. This introduces an infrared regulator for the photon in the standard electroweak theory, along with a modification of the weak mixing angle accompanied by a plethora of new effects. Notably, neutrinos couple to the photon and charged leptons have also a pseudo-vector coupling. Finally, we review the historical influence of Stueckelberg's 1938 idea, which led to applications in many areas not anticipated by the author, such as strings. We describe the numerous proposals to generalize the Stueckelberg trick to the non-Abelian case with the aim to find alternatives to the standard model. Nevertheless, the Higgs mechanism in spontaneous symmetry breaking remains the only presently known way to give masses to non-Abelian vector fields in a renormalizable and unitary theory.