Fault reactivation by fluid injection: Controls from stress state and injection rate

We studied the influence of stress state and fluid injection rate on the reactivation of faults. We conducted experiments on a saw-cut Westerly granite sample under triaxial stress conditions. Fault reactivation was triggered by injecting fluids through a borehole directly connected to the fault. Our results show that the peak fluid pressure at the borehole leading to reactivation depends on injection rate. The higher the injection rate, the higher the peak fluid pressure allowing fault reactivation. Elastic wave velocity measurements along fault strike highlight that high injection rates induce significant fluid pressure heterogeneities, which explains that the onset of fault reactivation is not determined by a conventional Coulomb law and effective stress principle, but rather by a nonlocal rupture initiation criterion. Our results demonstrate that increasing the injection rate enhances the transition from drained to undrained conditions, where local but intense fluid pressures perturbations can reactivate large faults

Phase space analysis and functional calculus for the linearized Landau and Boltzmann operators

In many works, the linearized non-cutoff Boltzmann operator is considered to behave essentially as a fractional Laplacian. In the present work, we prove that the linearized non-cutoff Boltzmann operator with Maxwellian molecules is exactly equal to a fractional power of the linearized Landau operator which is the sum of the harmonic oscillator and the spherical Laplacian. This result allows to display explicit sharp coercive estimates satisfied by the linearized non-cutoff Boltzmann operator for both Maxwellian and non-Maxwellian molecules.Comment: arXiv admin note: text overlap with arXiv:1111.042

On the Incidence of C IV Absorbers Along the Sightlines to Gamma-Ray Bursts

We report on the statistics of strong (W_r > 0.15 A) C IV absorbers at z=1.5-3.5 toward high-redshift gamma-ray bursts (GRBs). In contrast with a recent survey for strong Mg II absorption systems at z < 2, we find that the number of C IV absorbers per unit redshift dN/dz does not show a significant deviation from previous surveys using quasi-stellar objects (QSOs) as background sources. We find that the number density of C IV toward GRBs is dN/dz(z~1.5)= 2.2 +2.8/-1.4, dN/dz(z~2.5)= 2.3 +1.8/-1.1 and dN/dz(z~3.5)= 1.1 +2.6/-0.9. These numbers are consistent with previous C IV surveys using QSO spectra. Binning the entire dataset, we set a 95% c.l. upper limit to the excess of C IV absorbers along GRB sightlines at twice the incidence observed along QSO sightlines. Furthermore, the distribution of equivalent widths of the GRB and QSO samples are consistent with being drawn from the same parent population. Although the results for Mg II and C IV absorbers along GRB sightlines appear to contradict one another, we note that the surveys are nearly disjoint: the C IV survey corresponds to higher redshift and more highly ionized gas than the Mg II survey. Nevertheless, analysis on larger statistical samples may constrain properties of the galaxies hosting these metals (e.g. mass, dust content) and/or the coherence-length of the gas giving rise to the metal-line absorption.Comment: Accepted version (for publication in ApJ), results unchanged, 18 pages, 3 tables, 5 figure

Room temperature reversible C-H activation mediated by a Pt(0) center, and stoichiometric biphenyl formation via solvent activation.

International audienceRoom temperature reversible C-H activation mediated by a designed diphosphine platinum complex is presented. These findings are demonstrated through mechanistic studies involving kinetics, isotopic effects, and corroborated by DFT calculations. The coupling between two unactivated aromatic derivatives is also demonstrated

How higher-spin gravity surpasses the spin two barrier: no-go theorems versus yes-go examples

Aiming at non-experts, we explain the key mechanisms of higher-spin extensions of ordinary gravity. We first overview various no-go theorems for low-energy scattering of massless particles in flat spacetime. In doing so we dress a dictionary between the S-matrix and the Lagrangian approaches, exhibiting their relative advantages and weaknesses, after which we high-light potential loop-holes for non-trivial massless dynamics. We then review positive yes-go results for non-abelian cubic higher-derivative vertices in constantly curved backgrounds. Finally we outline how higher-spin symmetry can be reconciled with the equivalence principle in the presence of a cosmological constant leading to the Fradkin--Vasiliev vertices and Vasiliev's higher-spin gravity with its double perturbative expansion (in terms of numbers of fields and derivatives).Comment: LaTeX, 50 pages, minor changes, many refs added; version accepted for publication in Reviews of Modern Physic

Towards the Laboratory Search for Space-Time Dissipation

It has been speculated that gravity could be an emergent phenomenon, with classical general relativity as an effective, macroscopic theory, valid only for classical systems at large temporal and spatial scales. As in classical continuum dynamics, the existence of underlying microscopic degrees of freedom may lead to macroscopic dissipative behaviors. With the hope that such dissipative behaviors of gravity could be revealed by carefully designed experiments in the laboratory, we consider a phenomenological model that adds dissipations to the gravitational field, much similar to frictions in solids and fluids. Constraints to such dissipative behavior can already be imposed by astrophysical observations and existing experiments, but mostly in lower frequencies. We propose a series of experiments working in higher frequency regimes, which may potentially put more stringent bounds on these models.Comment: 18 pages, 8 figure

Dopaminergic neurons inhibit striatal output via non-canonical release of GABA

The substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) contain the two largest populations of dopamine (DA)-releasing neurons in the mammalian brain. These neurons extend elaborate projections in striatum, a large subcortical structure implicated in motor planning and reward-based learning. Phasic activation of dopaminergic neurons in response to salient or reward-predicting stimuli is thought to modulate striatal output via the release of DA to promote and reinforce motor action1–4. Here we show that activation of DA neurons in striatal slices rapidly inhibits action potential firing in both direct-and indirect-pathway striatal projection neurons (SPNs) through vesicular release of the inhibitory transmitter γ-aminobutyric acid (GABA). GABA is released directly from dopaminergic axons but in a manner that is independent of the vesicular GABA transporter VGAT. Instead GABA release requires activity of the vesicular monoamine transporter VMAT2, which is the vesicular transporter for DA. Furthermore, VMAT2 expression in GABAergic neurons lacking VGAT is sufficient to sustain GABA release. Thus, these findings expand the repertoire of synaptic mechanisms employed by DA neurons to influence basal ganglia circuits, reveal a novel substrate whose transport is dependent on VMAT2, and demonstrate that GABA can function as a bona fide co-transmitter in monoaminergic neurons