An investigation of Lagrangian Riemann methods incorporating material strength

The application of Riemann Methods formulated in the Lagrangian reference frame to the numerical simulation of non-linear events in solid materials is investigated. Here, solids are characterised by their ability to withstand shear distortion since they possess material strength. In particular, numerical techniques are discussed for simulating the transient response of solids subjected to extreme loading. In such circumstances, the response of solids will often be highly non-linear, displaying elastic and plastic behaviour, and even moderate compressions will produce strong shock waves.This work reviews the numerical schemes or 'hydrocodes' which have been adopted in the past in order to simulate such systems, identifying the advantages and limitations of such techniques. One of the most prominent limitations of conventional Lagrangian methods is that the computational mesh or grid has fixed-connectivity i.e. mesh nodes are connected to the same nodes for all time. This has significant disadvantages since the computational mesh can easily become tangled as the simulated material distorts. The majority of conventional hydrocodes are also constructed using outdated artificial viscosity schemes which are known to diffuse shock waves and other steep features which may be present in the solution.In the work presented here, a novel two-dimensional Lagrangian solver has been developed Vucalm-EP which overcomes many of the limitations of conventional techniques. By employing the Free-Lagrange Method, whereby the connectivity of the computational mesh is allowed to evolve as the material distorts, problems of arbitrarily large deformation can be simulated. With the implementation of a spatially second-order accurate, finite-volume, Godunov-type solver, non-linear waves such as shocks are represented with higher resolution than previously possible with contemporary schemes. The Vucalm-EP solver simulates the transient elastic-perfectly plastic response of solids and displays increased accuracy over alternative Lagrangian techniques developed to simulate large material distortion such as Smoothed particle Hydrodynamics (SPH). Via a variety of challenging numerical simulations the Vucalm-EP solver is compared with contemporary Euler, fixed-connectivity Lagrangian, and meshless SPH solvers. These simulations include the solution of one- and two dimensional shock tube problems in aluminium, simulating the collapse of cylindrical shells and modelling high-velocity projectile impacts. Validation against previously published results, solutions obtained using alternative numerical techniques and analytical models illustrates the versatility and accuracy of the technique. Thus, the Vucalm-EP solver provides a numerical scheme for the Lagrangian simulation of extensive material distortion in materials with strength, which has never previously been possible with mesh-based techniques

Work and the Disability Transition in 20th Century America

Using data from Union Army pensioners and from the National Health Interview Surveys, we estimate that work-disability among white males aged 45-64 was 3.5 times as high in the late 19th century than at the end of the 20th century, including a decline and flattening of the age-profile since 1970. We present a descriptive model of disability that can account for a) the secular decline in prevalence; b) changes in slope of the age-profile; and c) periods of increasing prevalence. The high level and relatively flat slope of the historical disability age-profile is consistent with the early onset of chronic conditions and with high mortality associated with a subset of those conditions. We show that many common conditions in the 19th century have been either eliminated, delayed to later ages, or rendered less disabling by treatment innovations and the transformation of the workplace. These improvements have swamped the effect of declining mortality, which put upward pressure on disability prevalence. Given the low rate of mortality prior to age 65, technological changes will likely induce further reductions in work-disability, though recent increases in the prevalence of asthma and obesity may eventually work against this trend.

Writing Center Space The First Frontier

This paper discusses the influence of writing center spaces on the impressions of tutors and students. First, the importance of creating a “homey” space is introduced, then followed by an example of a writing center thought by its denizens to be particularly welcoming and effective. An analysis of another writing center’s evolution and subsequent changes in impressions and use is included. Finally, scale is introduced as a foundational principle in the architectural field with particular application in creating a desired impression

Ground vibration near explosions

One would expect that, since seismic waves from explosions are the basis of a whole industry (seismic surveying), their nature would have been throughly investigated and described. However, the exploration geophysicist is not primarily interested in the nature of the seismic pulses, but in their velocities and the paths they travel to his recording instruments. It is common practice in studying seismic exploration records to assume that only compressional pulses are clearly recorded, though occasionally the presence of some transverse wave energy is postulated to explain otherwise incomprehensible observations. Other types of wave motion are treated as part of the background noise, and wherever possible are excluded from the recorded spectrum by the use of appropriate filters in the amplifiers

Imaging Studies of photodamage and self-healing in disperse orange 11 dye-doped PMMA

We report on optical imaging studies of self-healing after laser-induced photodamage in disperse orange 11 dye doped into poly(methyl methacrylate) (PMMA) polymer. In particular, the high spatial-contrast image of the damage track made by a line focus pump laser allows the recovery rates to be measured as a function of burn dose using the relationship between transverse distance and pump intensity profile. The time evolution of the damaged population results in an intensity-independent time constant of {\tau} = 490\pm23 min, in agreement with independent measurements of the time evolution of amplified spontaneous emission. Also observed is a damage threshold above which the material does not fully recover.Comment: 5 pages, 8 figure

Outcomes in Knot vs Knotless Surgery in Labrum Tears

A Bankart lesion is a tear of the anterior and inferior glenoid labrum. The primary method of repairing this lesion is to sew the detached part back to the joint, however there is a relatively newer method of doing so that does not involve tying a knot in the joint which may cause less joint irritation. The question our research project attempted to answer was: How do the long-term outcomes associated with knotless Bankart labrum repairs compare with the knot repairs? A retrospective cohort study was done with Rothman Institute Bankart lesion patients from 2010-2016. Data was gathered over phone calls and responses to certain categorical questions like motion, function, stability and return to OR were measured on a scale 0-3. The mean score of these categories was calculated and many of them were close to identical. One category where there was some degree of difference was stability (0=no subluxation, 3=recurrent dislocation). Those who had the knot surgery reported a mean of 1.53 level of instability and those who had the knotless surgery reported a mean of 1.13. It was previously hypothesized that the knotless surgery would have fewer detrimental effects and although this is possible with a lower instability rating, the results were not statistically significant since the p-value was 0.43. However, it is possible that this result can be clinically significant for surgeons when deciding which surgical technique to employ

The LCOGT Network

Motivated by the increasing need for observational resources for the study of time varying astronomy, the Las Cumbres Observatory Global Telescope (LCOGT) is a private foundation, whose goal is to build a global network of robotic telescopes for scientific research and education. Once completed, the network will become a unique tool, capable of continuous monitoring from both the Northern and Southern Hemispheres. The network currently includes 2 x 2.0 m telescopes, already making an impact in the field of exoplanet research. In the next few years they will be joined by at least 12 x 1.0 m and 20 x 0.4 m telescopes. The increasing amount of LCOGT observational resources in the coming years will be of great service to the astronomical community in general, and the exoplanet community in particular.Comment: 2 pages, 1 figure, to appear in the proceedings of IAU Symposium 276 "The Astrophysics of Planetary Systems: Formation, Structure, and Dynamical Evolution

S02, E02: Eviction Part 2 – The Longer Take

This podcast is a continuation of the podcast Eviction Part 1. It discusses cases of eviction, how the instability of housing impacts individuals and neighborhoods, section eight and how eviction is just the latest form of dispossession of people. It looks at neighborhoods in Richmond that have seen instability in some form over the last 100 years.https://scholarscompass.vcu.edu/civil_discourse/1007/thumbnail.jp

The association between neurodegeneration and local complement activation in the thalamus to progressive multiple sclerosis outcome

The extent of grey matter demyelination and neurodegeneration in the progressive multiple sclerosis (PMS) brains at post‐mortem associates with more severe disease. Regional tissue atrophy, especially affecting the cortical and deep grey matter, including the thalamus, is prognostic for poor outcomes. Microglial and complement activation are important in the pathogenesis and contribute to damaging processes that underlie tissue atrophy in PMS. We investigated the extent of pathology and innate immune activation in the thalamus in comparison to cortical grey and white matter in blocks from 21 cases of PMS and 10 matched controls. Using a digital pathology workflow, we show that the thalamus is invariably affected by demyelination and had a far higher proportion of active inflammatory lesions than forebrain cortical tissue blocks from the same cases. Lesions were larger and more frequent in the medial nuclei near the ventricular margin, whilst neuronal loss was greatest in the lateral thalamic nuclei. The extent of thalamic neuron loss was not associated with thalamic demyelination but correlated with the burden of white matter pathology in other forebrain areas (Spearman r = 0.79, p < 0.0001). Only thalamic neuronal loss, and not that seen in other forebrain cortical areas, correlated with disease duration (Spearman r = −0.58, p = 0.009) and age of death (Spearman r = −0.47, p = 0.045). Immunoreactivity for the complement pattern recognition molecule C1q, and products of complement activation (C4d, Bb and C3b) were elevated in thalamic lesions with an active inflammatory pathology. Complement regulatory protein, C1 inhibitor, was unchanged in expression. We conclude that active inflammatory demyelination, neuronal loss and local complement synthesis and activation in the thalamus, are important to the pathological and clinical disease outcomes of PMS