Impact of granular slugs on rigid targets: Effect of grain shape and fracture

The effect of grain shape and fracture on the interaction of high velocity granular slugs with rigid stationary targets is analysed for targets in normal and inclined orientations. The granular slugs comprise spherical, rod-shaped or cubic grains and are constructed by connecting together spherical sub-particles with either rigid or beam connectors. The case when grain fracture is suppressed (rigid connectors between sub-particles) is first analysed. With increasing grain aspect ratio, the grains tend to slide rather than roll on the target surface and this increases frictional interactions with the target surface. However, these enhanced frictional forces do not affect the momentum transmitted into normally oriented targets due to the symmetry of the problem. By contrast, the break in the symmetry for inclined targets results in the transmitted momentum increasing with grain aspect ratio. Fracture of the grains (as modelled by the fracture of the beam connectors between sub-particles) is shown to affect the momentum transmitted into the inclined targets. This is a consequence of fracture resulting in a change in grain shape. In this case the simulations show that the transmitted momentum is a function of the initial grain shape, the fracture properties of the grains and the impact velocity. In fact, grain fracture results in an enhanced transmitted momentum for initially cubic grains but fracture of grains with a high initial aspect ratio results in a reduction in transmitted momentum as these grains fragment into more spherically shaped grains

Momentum transfer during the impact of granular matter with inclined sliding surfaces

© 2017 Elsevier Ltd Increasing the inclination of a rigid surface that is impacted by a collimated granular flow reduces the fraction of granular matter momentum transferred to the surface. Recent studies have shown that the momentum reduction depends upon a frictional interaction between the granular flow and the impacted surface. High coefficient of friction surfaces suffer significantly more momentum transfer than predicted by resolution of the incident momentum onto the inclined plane. This discovery has raised the possibility that inclined surfaces with very low friction coefficients might reduce the impulsive transferred by the impact of high velocity granular matter. Here the use of a lubricated sliding plate is investigated as a means for reducing interfacial friction and impulse transfer to an inclined surface. The study uses a combination of experimental testing and particle-based simulations to investigate impulse transfer to rigid aluminum surfaces inclined either perpendicular or at 53° to synthetic sand that was impulsively accelerated to a velocity of 350–500 m/s. The study shows that impact of this sand with lubricated plates attached to an inclined surface rapidly accelerates them to a velocity of about 55–70 m/s, and reduces the impulse transferred to the inclined surface below. The reduction of impulse by this approach is comparable to that achieved by changing the inclination of the surface.This research was funded by the Defense Advanced Research Projects Agency (DARPA) under grant number W91CRB-11-1-0005 (Program manager, Dr. J. Goldwasser)

The Hexaemeron in Peter Comestor’s \u3cem\u3eHistoria Scholastica\u3c/em\u3e

As a part of the larger Historia Scholastica Project, we are transcribing and translating text from the “Genesis” chapter of the Historia Scholastica found in the Albertson’s Library. Our work began in fall of 2018. Our goal is to locate source material that informed Comestor’s understanding of the content of “Genesis” to better understand and therefore better translate Comestor. We are researching sources that possibly contributed to Comestor’s understanding of cosmology, philosophy, and the biblical creation account, in addition to transcribing and translating the text. Our methodology focuses on ten lines per week, applying textual criticism to identify textual differences and assist where our copy is damaged. We are using Patrologia Latinae 198, the Lugdunensis copy on Wiki, and the online Internet Archive of the Historia Scholastica located in Strasbourg, France. We then filter any possible translations through the lens of biblical studies taking place in medieval France in the late 12th and early 13th centuries. Our goal is to produce 100 lines of quality Latin by the end of the semester; to date we have completed approximately 40%. This project will provide groundwork for future researchers in other portions of the Historia Scholastica

Coupled discrete/continuum simulations of the impact of granular slugs with clamped beams: stand-off effects

Coupled discrete particle/continuum simulations of the normal (zero obliquity) impact of granular slugs against the centre of deformable, end-clamped beams are reported. The simulations analyse the experiments of Uth et al. (2015) enabling a detailed interpretation of their observations of temporal evolution of granular slug and a strong stand-off distance dependence of the structural response. The high velocity granular slugs were generated by the pushing action of a piston and develop a spatial velocity gradient due to elastic energy stored during the loading phase by the piston. The velocity gradient within the “stretching” slug is a strong function of the inter-particle contact stiffness and the time the piston takes to ramp up to its final velocity. Other inter-particle contact properties such as damping and friction are shown to have negligible effect on the evolution of the granular slug. The velocity gradients result in a slug density that decreases with increasing stand-off distance, and therefore the pressure imposed by the slug on the beams is reduced with increasing stand-off. This results in the stand-off dependence of the beam's deflection observed by Uth et al. (2015). The coupled simulations capture both the permanent deflections of the beams and their dynamic deformation modes with a high degree of fidelity. These simulations shed new light on the stand-off effect observed during the loading of structures by shallow-buried explosions

Guided Interface Waves

Many of tomorrow’s technologies are dependent upon the emergence of new advanced materials with superior stiffness and strength but reduced density. Metal matrix composites (MMC’s) consisting of light metal matrices (e. g., aluminum, titanium or magnesium) reinforced with very stiff ceramic fibers or particles (e. g. SiC, AI2O3 or graphite) show considerable promise for satisfying this need. However, the satisfactory performance of these materials has been found to be critically dependent upon the attainment of optimal properties at the metal-ceramic interface; a problem that is compounded by the possibility of chemical reactions between the reactive metal matrix and ceramic reinforcement. Of particular import are the interface adhesion and local elastic properties. Unfortunately no methods exist for the measurement of these quantities even for macroscopic interfaces let alone for the microscopic interfaces occurring within MMC’s

Blood Pressure and Cognitive Decline Over 8 Years in Middle-Aged and Older Black and White Americans

Although the association between high blood pressure (BP), particularly in midlife, and late-life dementia is known, less is known about variations by race and sex. In a prospective national study of 22 164 blacks and whites ≥45 years without baseline cognitive impairment or stroke from the REGARDS cohort study (Reasons for Geographic and Racial Differences in Stroke), enrolled 2003 to 2007 and followed through September 2015, we measured changes in cognition associated with baseline systolic and diastolic BP (SBP and DBP), as well as pulse pressure (PP) and mean arterial pressure, and we tested whether age, race, and sex modified the effects. Outcomes were global cognition (Six-Item Screener; primary outcome), new learning (Word List Learning), verbal memory (Word List Delayed Recall), and executive function (Animal Fluency Test). Median follow-up was 8.1 years. Significantly faster declines in global cognition were associated with higher SBP, lower DBP, and higher PP with increasing age ( P<0.001 for age×SBP×follow-up-time, age×DBP×follow-up-time, and age×PP×follow-up-time interaction). Declines in global cognition were not associated with mean arterial pressure after adjusting for PP. Blacks, compared with whites, had faster declines in global cognition associated with SBP ( P=0.02) and mean arterial pressure ( P=0.04). Men, compared with women, had faster declines in new learning associated with SBP ( P=0.04). BP was not associated with decline of verbal memory and executive function, after controlling for the effect of age on cognitive trajectories. Significantly faster declines in global cognition over 8 years were associated with higher SBP, lower DBP, and higher PP with increasing age. SBP-related cognitive declines were greater in blacks and men