Tectonics and seismicity in the Northern Apennines driven by slab retreat and lithospheric delamination

Understanding how long-term subduction dynamics relates to the short-term seismicity and crustal tec tonics is a challenging but crucial topic in seismotectonics. We attempt to address this issue by linking long-term geodynamic evolution with short-term seismogenic deformation in the Northern Apennines. This retreating subduction orogen displays tectonic and seismogenic behaviors on various spatiotemporal scales that also characterize other subduction zones in the Mediterranean area. We use visco-elasto-plastic seismo-thermo-mechanical (STM) modeling with a realistic 2D setup based on available geological and geophysical data. The subduction dynamics and seismicity are coupled in the numerical modeling, and driven only by buoyancy forces, i.e., slab pull. Our results suggest that lower crustal rheology and lithospheric mantle temperature modulate the crustal tectonics of the Northern Apennines, as inferred by previous studies. The observed spatial distribution of upper crustal tectonic regimes and surface displacements requires buoyant, highly ductile material in the subduction channel beneath the internal part of the orogen. This allows protrusion of the asthenosphere in the lower crust and lithospheric delamination associated with slab retreat. The resulting surface velocities and principal stress axes generally agree with present-day observations, suggesting that slab delamination and retreat can explain the dynamics of the orogen. Our simulations successfully reproduce the type and overall distribution of seismicity with thrust faulting events in the external part of the orogen and normal faulting in its internal part. Slab temperatures and lithospheric mantle stiffness affect the cumulative seismic moment release and spatial distribution of upper crustal earthquakes. The properties of deep, sub-crustal material are thus shown to influence upper crustal seismicity in an orogen driven by slab retreat, even though the upper crust is largely decoupled from the lithospheric mantle. Our simulations therefore highlight the effect of deep lower crustal rheologies, self-driven subduction dynamics and mantle properties in controlling shallow deformation and seismicity

Dual chaperone role of the c-terminal propeptide in folding and oligomerization of the pore-forming toxin aerolysin

Throughout evolution, one of the most ancient forms of aggression between cells or organisms has been the production of proteins or peptides affecting the permeability of the target cell membrane. This class of virulence factors includes the largest family of bacterial toxins, the pore-forming toxins (PFTs). PFTs are bistable structures that can exist in a soluble and a transmembrane state. It is unclear what drives biosynthetic folding towards the soluble state, a requirement that is essential to protect the PFT-producing cell. Here we have investigated the folding of aerolysin, produced by the human pathogen Aeromonas hydrophila, and more specifically the role of the C-terminal propeptide (CTP). By combining the predictive power of computational techniques with experimental validation using both structural and functional approaches, we show that the CTP prevents aggregation during biosynthetic folding. We identified specific residues that mediate binding of the CTP to the toxin. We show that the CTP is crucial for the control of the aerolysin activity, since it protects individual subunits from aggregation within the bacterium and later controls assembly of the quaternary pore-forming complex at the surface of the target host cell. The CTP is the first example of a C-terminal chain-linked chaperone with dual function

Disentangling the electronic and phononic glue in a high-Tc superconductor

Unveiling the nature of the bosonic excitations that mediate the formation of Cooper pairs is a key issue for understanding unconventional superconductivity. A fundamen- tal step toward this goal would be to identify the relative weight of the electronic and phononic contributions to the overall frequency (\Omega) dependent bosonic function, \Pi(\Omega). We perform optical spectroscopy on Bi2212 crystals with simultaneous time- and frequency-resolution; this technique allows us to disentangle the electronic and phononic contributions by their different temporal evolution. The strength of the interaction ({\lambda}~1.1) with the electronic excitations and their spectral distribution fully account for the high critical temperature of the superconducting phase transition.Comment: 9 pages, 4 figure

Correlation effects in single-particle overlap functions and one-nucleon removal reactions

Single-particle overlap functions and spectroscopic factors are calculated on the basis of the one-body density matrices (ODM) obtained for the nucleus $^{16}O$ employing different approaches to account for the effects of correlations. The calculations use the relationship between the overlap functions related to bound states of the (A-1)-particle system and the ODM for the ground state of the A-particle system. The resulting bound-state overlap functions are compared and tested in the description of the experimental data from (p,d) reactions for which the shape of the overlap function is important.Comment: 11 pages, 4 figures include

On the accretion flow geometry in A0535+26

The geometry of accretion flow in the Be/X-ray transient A0535+26 is explored. It is shown that neither moderate nor giant X-ray flaring events observed in the system can be interpreted within the spherically symmetrical accretion model and hence the formation of an accretion disk around the neutron star magnetosphere during the both types of flares is required. The accretion disk can be formed at the periastron if (i) the expansion velocity of the Be star envelope in the equatorial plane is V_wr < 150 km/s and (ii) the parameter accounting for the accretion flow inhomogeneities, xi, satisfies the following condition: xi > 0.16 (Mdot_17)^-1/7, where (Mdot_17)^-1/7 is the rate of mass capture by the neutron star expressed in units of 1017 g/s. We suggest that the `missing' outburst phenomenon can be associated with the spherically symmetrical accretion onto the interchange-stable magnetosphere of the neutron star. The average spin up rate of the neutron star during moderate flares < 3.5 x 10^-12 Hz/s is predicted.Comment: 6 pages, published in A&A 372, 227 (2001

Magnetic Field Upper Limits for Jet Formation

Context: Very high magnetic fields at the surface of neutron stars or in the accretion disk of black holes inhibit the production of jets. Aims: We quantify here the magnetic field strength for jet formation. Methods: By using the Alfven Radius, R_A, we study what we call {\it the basic condition}, R_A/R_*=1 or R_A/R_{LSO}=1 (LSO, last stable orbit), in its dependency on the magnetic field strength and the mass accretion rate, and we analyse these results in 3-D and 2-D plots in the case of neutron star and black hole accretor systems, respectively. For this purpose, we did a systematic search of all available observational data for magnetic field strength and the mass accretion rate. Results: The association of a classical X-ray pulsar (i.e. B ~10^{12} G) with jets is excluded even if accreting at the Eddington critical rate. Z-sources may develop jets for B \simlt 10^{8.2} G, whereas Atoll-sources are potential sources of jets if B \simlt 10^{7.7} G. It is not ruled out that a millisecond X-ray pulsar could develop jets, at least for those sources where B \simlt 10^{7.5} G. In this case the millisecond X-ray pulsar could switch to a microquasar phase during its maximum accretion rate. For stellar-mass black hole X-ray binaries, the condition is that B \simlt 1.35 x 10^8 G and B \simlt 5 x 10^8 G at the last stable orbit for a Schwarzschild and a Kerr black hole, respectively. For active galactic nuclei (AGNs), it reaches B \simlt 10^{5.9} G for each kind of black hole. These theoretical results are in complete agreement with available observational data.Comment: 7 pages, 6 figures, A&A in press. Version 2 with minor correction