Rate dependent shear bands in a shear transformation zone model of amorphous solids

We use Shear Transformation Zone (STZ) theory to develop a deformation map for amorphous solids as a function of the imposed shear rate and initial material preparation. The STZ formulation incorporates recent simulation results [Haxton and Liu, PRL 99 195701 (2007)] showing that the steady state effective temperature is rate dependent. The resulting model predicts a wide range of deformation behavior as a function of the initial conditions, including homogeneous deformation, broad shear bands, extremely thin shear bands, and the onset of material failure. In particular, the STZ model predicts homogeneous deformation for shorter quench times and lower strain rates, and inhomogeneous deformation for longer quench times and higher strain rates. The location of the transition between homogeneous and inhomogeneous flow on the deformation map is determined in part by the steady state effective temperature, which is likely material dependent. This model also suggests that material failure occurs due to a runaway feedback between shear heating and the local disorder, and provides an explanation for the thickness of shear bands near the onset of material failure. We find that this model, which resolves dynamics within a sheared material interface, predicts that the stress weakens with strain much more rapidly than a similar model which uses a single state variable to specify internal dynamics on the interface.Comment: 10 pages, 13 figures, corrected typos, added section on rate strengthening vs. rate weakening material

Strain localization in a shear transformation zone model for amorphous solids

We model a sheared disordered solid using the theory of Shear Transformation Zones (STZs). In this mean-field continuum model the density of zones is governed by an effective temperature that approaches a steady state value as energy is dissipated. We compare the STZ model to simulations by Shi, et al.(Phys. Rev. Lett. 98 185505 2007), finding that the model generates solutions that fit the data,exhibit strain localization, and capture important features of the localization process. We show that perturbations to the effective temperature grow due to an instability in the transient dynamics, but unstable systems do not always develop shear bands. Nonlinear energy dissipation processes interact with perturbation growth to determine whether a material exhibits strain localization. By estimating the effects of these interactions, we derive a criterion that determines which materials exhibit shear bands based on the initial conditions alone. We also show that the shear band width is not set by an inherent diffusion length scale but instead by a dynamical scale that depends on the imposed strain rate.Comment: 8 figures, references added, typos correcte

The contribution of helicopter emergency medical services in the pre-hospital care of penetrating torso injuries in a semi-rural setting

BACKGROUND: Although the merit of pre-hospital critical care teams such as Helicopter Emergency Medical Services (HEMS) has been universally recognized for patients with penetrating torso injuries who present with unstable physiology, the potential merit in patients initially presenting with stable physiology is largely undetermined. The ability to predict the required pre-hospital interventions patients may have important implications for HEMS tasking, especially when transport times to definitive care are prolonged. METHODS: We performed a retrospective cohort study of patients who sustained a penetrating torso injury and were attended by the Air Ambulance Kent Surrey Sussex (AAKSS) over a 6-year period. Primary outcome was defined as the percentage of patients with penetrating torso injuries requiring HEMS-specific interventions anytime between HEMS arrival and arrival at hospital. Secondary outcomes were the association of individual patient- and injury characteristics with the requirement for HEMS interventions. RESULTS: During the study period 363 patients met inclusion criteria. 90% of patients were male with a median age of 30 years. 99% of penetrating trauma incident occurred more than 10-min drive from a Major Trauma Centre (MTC). Presenting GCS was > 13 in 83% of patients. Significant hemodynamic- or ventilatory compromise was present in more than 25% of the patients. Traumatic cardiac arrest was present in 34 patients (9.4%), profound hypotension with SBP < 80 mmHg in 30 (8.3%) and oxygen saturations < 92% in 30 (8.3%). A total of 121 HEMS-specific interventions were performed. Although HEMS-specific interventions were associated with presenting physiology (TCA OR 1.75 [1.41–2.16], SBP < 80 mmHg (OR 1.40 [1.18–1.67] and SpO(2) < 92% (OR 1.39 [1.17–1.65], a minority of the patients presented initially with stable physiology but deteriorated on route to hospital and required HEMS interventions (n = 9, 3.3%). CONCLUSION: HEMS teams provide potentially important contribution to the pre-hospital treatment of patients with penetrating torso injuries in rural and semi-rural areas, especially when they present with unstable physiology. A certain degree of over-triage is inevitable in these patients, as it is hard to predict which patients will deteriorate on route to hospital and will need HEMS interventions. The results of this study showing a potentially predictable geographical dispersion of penetrating trauma could inform multi-agency knife crime prevention strategy

Improved fluid dynamics similarity, analysis and verification. Part 4 - Acoustic velocities in two-phase mixtures of some cryogenic fluids Final report, 29 Jun. 1965 - 28 Jun. 1968

Model calculations and graphical presentation of acoustic velocities in two-phase mixtures of some cryogenic fluid

Anti-Pasch optimal packings with triples

It is shown that for v ≠ 6, 7, 10, 11, 12, 13, there exists an optimal packing with triples on v points that contains no Pasch configurations. Furthermore, for all v ≡ 5 (mod 6), there exists a pairwise balanced design of order v, whose blocks are all triples apart from a single quintuple, and that has no Pasch configurations amongst its triples

Combretastatin-A4 disrupts neovascular development in non-neoplastic tissue

Combretastatin-A4 phosphate (cis -CA-4) is a tubulin-binding agent currently undergoing clinical trials as an anti-tumour drug. We have investigated whether CA-4 functions as a tumour-specific anti-vascular agent using the hyperplastic thyroid as a novel in vivo model of neovascularization. CA-4 elicited pathological changes in normal tissue, manifested as the induction of multiple, discrete intravascular thrombi. These vascular-damaging effects indicate that CA-4P does not function as a tumour-specific agent but targets neovasculature irrespective of the primary angiogenic stimulus. © 2001 Cancer Research Campaign http://www.bjcancer.co

Nitrogen Fertilization and Glyphosate-Resistant Alfalfa Termination Method Effects on First-Year Silage Corn

Tillage type/timing and herbicide application date may change the amount and timing of N mineralization, altering fertilizer N needs for first-year corn (Zea mays L.) following glyphosate [N-(phosphonomethyl)glycine]-resistant (GR) alfalfa (Medicago sativa L.). Studies were conducted in 2012 and 2013 in Utah. Yield, quality, and economic return of silage corn as affected by five tillage type/timings (fall conventional till, spring conventional till, fall strip-till, spring strip-till, and no-till), three herbicide application dates for alfalfa termination (fall, spring, and in-crop), and four N rates (0, 56, 112, and 224 kg ha−1) were evaluated. Silage corn yield and quality following GR alfalfa was economically optimized without N fertilization regardless of tillage type/timing and herbicide application date. Thus, N from decomposing alfalfa can provide the full N requirement of first-year silage corn following GR alfalfa. Estimated animal milk production ha−1 of silage corn was greatest and similar for all herbicide application dates with conventional tillage and spring herbicide application with strip-till and no-till (26–38 Mg milk ha−1), whereas an in-crop herbicide application with strip-till and no-till resulted in the lowest estimated milk production (21–29 Mg milk ha−1). Increased economic return for the in-crop herbicide date by including economics from harvesting the first alfalfa cutting before planting corn mostly offset the reduced economic return of the lower silage corn yield. Therefore, an application of 2,4-D (2,4-dichlorophenoxyacetic acid) and dicamba (3,6-dichloro-2-methoxybenzoic acid) in the fall, spring, or in-crop to control GR alfalfa are good economic options for conventional tillage, strip-till, and no-till systems