Venous injury and subsequent venous stenosis formation are responsible for hemodialysis graft failure. Our hypothesis is that these pathological changes are in part related to changes in wall shear stress (WSS) that results in the activation of matrix regulatory proteins causing subsequent venous stenosis formation. In the present study, we examined the serial changes in WSS, blood flow, and luminal vessel area that occur subsequent to the placement of a hemodialysis graft in a porcine model of chronic renal insufficiency. We then determined the corresponding histological, morphometric, and kinetic changes of several matrix regulatory proteins including VEGF-A, its receptors, matrix metalloproteinase (MMP)-2, MMP-9, tissue inhibitor of matrix metalloproteinase (TIMP)-1, and TIMP-2. WSS was estimated by obtaining blood flow and luminal vessel area by performing phase-contrast MRI with magnetic resonance angiography in 21 animals at 1 day after graft placement and prior to death on day 3 ( n = 7), day 7 ( n = 7), and day 14 ( n = 7). At all time points, the mean WSS at the vein-to-graft anastomosis was significantly higher than that at the control vein ( P < 0.05). WSS had a bimodal distribution with peaks on days 1 and 7 followed by a significant reduction in WSS by day 14 ( P < 0.05 compared with day 7) and a decrease in luminal vessel area compared with control vessels. By day 3, there was a significant increase in VEGF-A and pro-MMP-9 followed by, on day 7, increased pro-MMP-2, active MMP-2, and VEGF receptor (VEGFR)-2 ( P < 0.05) and, by day 14, increased VEGFR-1 and TIMP-1 ( P < 0.05) at the vein-to-graft anastomosis compared with control vessels. Over time, the neointima thickened and was composed primarily of α-smooth muscle actin-positive cells with increased cellular proliferation. Our data suggest that hemodialysis graft placement leads to early increases in WSS, VEGF-A, and pro-MMP-9 followed by subsequent increases in pro-MMP-2, active MMP-2, VEGFR-1, VEGFR-2, and TIMP-1, which may contribute to the development of venous stenosis.

By means of a finite elements technique we solve numerically the dynamics of an amorphous solid under deformation in the quasistatic driving limit. We study the noise statistics of the stress-strain signal in the steady-state plastic flow, focusing on systems with low internal dissipation. We analyze the distributions of avalanche sizes and durations and the density of shear transformations when varying the damping strength. In contrast to avalanches in the overdamped case, dominated by the yielding point universal exponents, inertial avalanches are controlled by a nonuniversal damping-dependent feedback mechanism, eventually turning negligible the role of correlations. Still, some general properties of avalanches persist and new scaling relations can be proposed.

Both OSR and HR are viable options if endovascular procedures fail or are not feasible. Palma vein bypass and femoroiliac or iliocaval PTFE bypasses have excellent outcomes with good symptomatic relief.

We study the linear elastic response of harmonic disk packings near jamming via three types of probes: (i) point forcing, (ii) constrained homogeneous deformation of subregions of large systems, and (iii) unconstrained deformation of the full system subject to periodic boundary conditions. For the point forcing, our results indicate that the transverse component of the response is governed by a lengthscale ξT, which scales with the confining pressure, p, as ξT∼p-0.25, while the longitudinal component is governed by ξL, which scales as ξL∼p-0.4. The former scaling is precisely the transverse lengthscale, which has been invoked to explain the structure of normal modes near the density of states anomaly in sphere packings, while the latter is much closer to the rigidity length, l*∼p-0.5, which has been invoked to describe the jamming scenario. For the case of constrained homogeneous deformation, we find that μ(R), the value of the shear modulus measured in boxes of size R, gives a value much higher than the continuum result for small boxes and recedes to its continuum limit only for boxes bigger than a characteristic length, which scales like p-0.5, precisely the same way as l*. Finally, for the case of unconstrained homogeneous deformation, we find displacement fields with power spectra, which are consistent with independent, uncorrelated Eshelby transformations. The transverse sector is amazingly invariant with respect to p and very similar to what is seen in Lennard-Jones glasses. The longitudinal piece, however, is sensitive to p. It develops a plateau at long wavelength, the start of which occurs at a length that grows in the p→0 limit. Strikingly, the same behavior is observed both for applied shear and dilation.

Fluid invasion in stressed materials can activate processes of mechanical failure due to changes in pore pressure (Eaton, 2018;Goebel & Brodsky, 2018). This phenomenon is accountable for fluid-induced seismicity related to enhanced geothermal systems (EGS) (

A simple finite-element analysis with varying damping strength is used to model the athermal shear rheology of densely packed glassy systems at a continuum level. We focus on the influence of dissipation on bulk rheological properties. Our numerical studies, done over a wide range of damping coefficients, identify two well-separated rheological regimes along with a crossover region controlled by a critical damping. In the overdamped limit, inertial effects are negligible and the rheological response is well described by the commonly observed Herschel-Bulkley equation. In stark contrast, inertial vibrations in the underdamped regime prompt a significant drop in the mean-stress level, leading to a nonmonotonic constitutive relation. The observed negative slope in the flow curve, which is a signature of mechanical instability and thus permanent shear banding, arises from the sole influence of inertia, in qualitative agreement with the recent molecular dynamics study of Nicolas et al., Phys. Rev. Lett. 116, 058303 (2016).

Recent experiments (Le Bouil et al., Phys. Rev. Lett., 2014, 112, 246001) have analyzed the statistics of local deformation in a granular solid undergoing plastic deformation. Experiments report strongly anisotropic correlation between events, with a characteristic angle that was interpreted using elasticity theory and the concept of Eshelby transformations with dilation; interestingly, the shear bands that characterize macroscopic failure occur at an angle that is different from the one observed in microscopic correlations. Here, we interpret this behavior using a mesoscale elastoplastic model of solid flow that incorporates a local Mohr-Coulomb failure criterion. This differs from the interpretation of Le Bouil et al., which is based on purely elastic considerations ignoring the potential role of local friction on deformation patterns. We show that the angle observed in the microscopic correlations can be understood by combining the elastic interactions associated with Eshelby transformation with the local failure criterion. At large strains, we also induce permanent shear bands at an angle that is different from the one observed in the correlation pattern. We interpret this angle as the one that leads to the maximal instability of slip lines.

Fluid-driven seismicity typically refers to (minor) seismic events that (partially) involve fluid flows. Examples range from natural flows associated with rainfalls and volcanic eruptions to human-made contexts including wastewater injection wells, hydraulic fracturing, and geothermal power plants. Recently, anthropogenic sources have lead to an extraordinary surge of seismic activities in different parts of the United States (Ellsworth, 2013). The most extreme cases are reported in Oklahoma and southern Kansas where most seismic events are potentially linked to large-scale wastewater disposals. In this context, it is essential to distinguish between seismic events that are a direct or primary consequence of the fluid injections due to the associated increase in shear stress and/or pore pressure, for example, and those that are instead triggered from these or other seismic events due to static and/or dynamic stress changes, for example, commonly denoted as aftershocks. Identifying these and the specific underlying event-event triggering mechanisms has important consequences in terms of seismic hazard assessment, earthquake forecasting, and effective mitigation strategies.To what extent fluid-based anthropogenic seismicity bears similarities with its natural analog is an open question. Swarm-like features of induced seismicity associated with wastewater disposal and/or hydraulic