Explore the vast range of titles available.

Magma viscosity strongly controls the style (for example, explosive versus effusive) of a volcanic eruption and thus its hazard potential, but can only be measured during or after an eruption. The identification of precursors indicative of magma viscosity would enable forecasting of the eruption style and the scale of associated hazards 1 . The unanticipated May 2018 rift intrusion and eruption of Kīlauea Volcano, Hawai‘i 2 displayed exceptional chemical and thermal variability in erupted lavas, leading to unpredictable effusion rates and explosivity. Here, using an integrated analysis of seismicity and magma rheology, we show that the orientation of fault-plane solutions (which indicate a fault’s orientation and sense of movement) for earthquakes preceding and accompanying the 2018 eruption indicate a 90-degree local stress-field rotation from background, a phenomenon previously observed only at high-viscosity eruptions 3 , and never before at Kīlauea 4 – 8 . Experimentally obtained viscosities for 2018 products and earlier lavas from the Pu‘u ‘Ō‘ō vents tightly constrain the viscosity threshold required for local stress-field reorientation. We argue that rotated fault-plane solutions in earthquake swarms at Kīlauea and other volcanoes worldwide provide an early indication that unrest involves magma of heightened viscosity, and thus real-time monitoring of the orientations of fault-plane solutions could provide critical information about the style of an impending eruption. Furthermore, our results provide insight into the fundamental nature of coupled failure and flow in complex multiphase systems. Rotated fault-plane solutions in earthquake swarms at volcanoes could provide an early indication of relatively viscous magma, and hence of the style and hazard potential of an impending eruption.

Ferrovolcanism, yet to be directly observed, is the most exotic and poorly understood predicted manifestation of planetary volcanism. Large-scale experiments carried out at the Syracuse Lava Project offer insight into the emplacement dynamics of metallic flows as well as coeval metallic and silicate flows. Here, we find that, under the same environmental conditions, higher-density/lower-viscosity metallic lava moves ten times faster than lower-density/higher-viscosity silicate lava. The overall morphology of the silicate flow is not significantly affected by the co-emplacement of a metallic flow. Rather, the metallic flow is largely decoupled from the silicate flow, occurring mainly in braided channels underneath the silicate flow and as low-relief breakouts from the silicate flow front. Turbulent interactions at the metallic-silicate flow interface result in mingling of the two liquids, preserved as erosional surfaces and sharp contacts. The results have important implications for the interpretation of possible ferrovolcanic landscapes across our solar system. Ferrovolcanism is a hypothetical form of planetary volcanism in which the erupted lava is metallic in composition. Here we show that ferrovolcanic lava is denser and less viscous than silicate lava, resulting in fast-moving, thin, braided flows.

We estimated the rheology of an active basaltic lava flow in the field, and compared it with experimental measurements carried out in the laboratory. In the field we mapped, sampled, and recorded videos of the 2014 flow on the southern flank of Pacaya, Guatemala. Velocimetry data extracted from videos allowed us to determine that lava traveled at ∼2.8 m/s on the steep ∼45° slope 50 m from the vent, while 550 m further downflow it was moving at only ∼0.3 m/s on a ∼4° slope. Estimates of effective viscosity based on Jeffreys’ equation increased from ∼7600 Pa s near the vent to ∼28,000 Pa s downflow. In the laboratory, we measured the viscosity of a representative lava composition using a concentric cylinder viscometer, at five different temperatures between 1234 and 1199 °C, with crystallinity increasing from 0.1 to 40 vol%. The rheological data were best fit by power law equations, with the flow index decreasing as crystal fraction increased, and no detectable yield strength. Although field-based estimates are based on lava characterized by a lower temperature, higher crystal and bubble fraction, and with a more complex petrographic texture, field estimates and laboratory measurements are mutually consistent and both indicate shear-thinning behavior. The complementary field and laboratory data sets allowed us to isolate the effects of different factors in determining the rheological evolution of the 2014 Pacaya flows. We assess the contributions of cooling, crystallization, and changing ground slope to the 3.7-fold increase in effective viscosity observed in the field over 550 m, and conclude that decreasing slope is the single most important factor over that distance. It follows that the complex relations between slope, flow velocity, and non-Newtonian lava rheology need to be incorporated into models of lava flow emplacement.

Non-spherical particles suspended in fluid flows are subject to hydrodynamic torques generated by fluid velocity gradients. For small axisymmetric particles, the most popular formulation of hydrodynamic torques is that given by Jeffery (Proc R Soc Lond A 102:161–179, 1922), which is valid for uniform shear flow in the viscous Stokes regime. In the lack of simple alternative formulations outside the Stokes regime, the Jeffery formulation has been widely applied to inertial particles in turbulent flows, where it is bound to produce inaccurate results. In this paper we quantify the statistical error incurred when the Jeffery formulation is used to study the motion of elongated axisymmetric particles under nonlinear shear flow conditions. Considering the archetypical case of prolate ellipsoidal particles in turbulent channel flow, we show that error for ellipsoids of the same length, l, as the Kolmogorov scale of the flow, ηK, is indeed small (order 1%) but increases exponentially up to l≃10ηK before becoming almost independent of elongation.

In this study, we examine the channel-fed ‘a‘ā lava flow system that was emplaced during a very short (less than 15 h long) eruption at Piton de la Fournaise (La Réunion) in December 2010. The system had four branches, the longest of which was 1100 m long. Three branches were emplaced over a smooth-surfaced pāhoehoe flow field with a vertical relief of 1–2 m and did not undergo burial by subsequent events. The fourth branch erupted from the same vent as the 1957 eruption and re-used the pre-existing channels of that eruption. In the proximal–medial sections of the three systems that were unconfined, we identified channelized flow sections that were characterized by the presence of either a single channel or multiple braided channels. These fed short (30–260 m long) zones of dispersed flow in the distal sections. We subsequently investigated the role of lava rheology (as controlled by downflow variations in crystal and bubble content) and pre-existing topography in triggering the transitions between single-channel and braided channel flow sections. Crystal content was 10 to 70 vol% and vesicle content was 18 to 55 vol%; cooling rates over distance (derived from glass chemistry) were 11 °C/km to 27 °C/km. However, downflow textural and thermal evolution appeared to neither affect, nor be affected by, whether the channel was single or braided. Instead, the channel network architecture could be related to even modest underlying slope variations. Here, a slope increase resulted in channel confluence, and a slope decrease resulted in channel bifurcation. This process was reversible, in that downflow slope variation could drive the channel network architecture to switch back and forth between a single channel and multiple braided channels several times along its length. Dispersed flow is always present immediately behind the flow front, irrespective of underlying topography. Three previous studies of basaltic lava flows found that steeper slopes favored braided channels, the opposite of what was observed here. We suggest that the underlying substrate and lava type may exert a control on this behavior, but further studies remain necessary.

AbstractOlder persons with chronic kidney disease (CKD) undergoing hemodialysis represent a growing portion of patients characterized by high vulnerability but still marginally studied. This study aimed at exploring the relationship between the number of prescriptions and fractures in older patients with CKD undergoing hemodialysis. A 24-item Frailty Index (FI) based on sociodemographic, clinical and biological data was computed. Unadjusted and adjusted logistic regression models were performed to test the association of prescribed medications with history of fractures. A total of 107 older patients undergoing hemodialysis (38 [35.5%] women, mean age 79.1 standard deviation, SD=7.7) were included in the study. Mean number of prescribed medications was 9.9 (SD=3.9) and was significantly associated with fractures (OR 1.18, 95% CI 1.06–1.32, p=0.003), even after adjustment for potential confounders (OR 1.16, 95% CI 1.03–1.30, p=0.016). If these results will be confirmed, interventions based on deprescribing will become essential in older persons undergoing hemodialysis.

A dilute suspension (volume fraction 0.05%) of rod-like particles in a turbulent backward-facing step flow at Reynolds number ReH=14900, is investigated by means of Particle Image Velocimetry. Two-way interactions between fluid and dispersed phase are analyzed by exploiting the high spatial resolution of the acquisitions. Mutual interactions between phases can be investigated by considering flow turbulence modulations and phenomena related to preferential concentration and orientation of fibers. Slight turbulence enhancement is reported in the laden flow and concentration data show a moderate tendency of fibers to accumulate at the channel centreline. Orientation data display a strong preferential orientation of fibers. Local fiber orientation is correlated to the direction of maximum shear showing a high level of correlation also in the flow regions featuring strong gradients.

Summary The objective of this paper is to study the influence of dispersed micrometer size particles on turbulent heat transfer mechanisms in wall-bounded flows. The strategic target of the current research is to set up a methodology to size and design new-concept heat transfer fluids with properties given by those of the base fluid modulated by the presence of dynamically-interacting, suitably-chosen, discrete micro- and nano-particles. We ran direct numerical simulations for hydrodynamically fully developed, thermally developing turbulent channel flow at shear Reynolds number Re τ = 150 and Prandtl number Pr = 3, and we tracked two large swarms of particles, characterized by different inertia and thermal inertia. Preliminary results on velocity and temperature statistics for both phases show that, with respect to single-phase flow, heat transfer fluxes at the walls increase by roughly 2% when the flow is laden with the smaller particles, which exhibit a rather persistent stability against non-homogeneous distribution and near-wall concentration. An opposite trend (slight heat transfer flux decrease) is observed when the larger particles are dispersed into the flow. These results are consistent with previous experimental findings and are discussed in the frame of the current research activities in the field. Future developments are also outlined.

The improvement of early vigour is crucial for the adaptation of maize (Zea mays L.) to the climatic conditions of central Europe and the northern Mediterranean, where early sowing is an important strategy for avoiding the effect of summer drought. The objectives of this study were to identify quantitative trait loci (QTL) controlling cold-related traits and to investigate the relationships among them. A set of 168 F2:4 families of the Lo964 x Lo1016 cross was grown in a sand-vermiculite substrate at 15/13°C (day/night) until the one-leaf stage. Twenty QTL were identified for the four shoot and two seed traits examined. Analysis of root weight and digital measurements of the length and diameter of primary and seminal roots led to the identification of 40 QTL. The operating efficiency of photosystem II (PSII) was related to seedling dry weight at both the phenotypic and genetic level (r=0.46, two matching loci, respectively) but was not related to root traits. Cluster analysis and QTL association revealed that the different root traits were largely independently inherited and that root lengths and diameters were mostly negatively correlated. The major QTL for root traits detected in an earlier study in hydroponics were confirmed in this study. The length of the primary lateral roots was negatively associated with the germination index (r=¡0.38, two matching loci). Therefore, we found a large number of independently inherited loci suitable for the improvement of early seedling growth through better seed vigour and/or a higher rate of photosynthesis.

Recent experiments in a turbulent boundary layer by Gerashchenko et al. (J. Fluid Mech., vol. 617, 2008, pp. 255–281) showed that the variance of inertial particle accelerations in the near-wall region increased with increasing particle inertia, contrary to the trend found in homogeneous and isotropic turbulence. This behaviour was attributed to the non-trivial interaction of the inertial particles with both the mean shear and gravity. To investigate this issue, we perform direct numerical simulations of channel flow with suspended inertial particles that are tracked in the Lagrangian frame of reference. Three simulations have been carried out considering (i) fluid particles, (ii) inertial particles with gravity and (iii) inertial particles without gravity. For each set of simulations, three particle response times were examined, corresponding to particle Stokes numbers (in wall units) of 0.9, 1.8 and 11.8. Mean and r.m.s. profiles of particle acceleration computed in the simulation are in qualitative (and in several cases quantitative) agreement with the experimental results, supporting the assumptions made in the simulations. Furthermore, by comparing results from simulations with and without gravity, we are able to isolate and quantify the significant effect of gravitational settling on the phenomenon.