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

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

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

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

Determinants of prehospital lactate in trauma patients:A retrospective cohort study

Background: Point of care serum lactate measurement is emerging as an adjunct to prehospital clinical assessment and has the potential to guide triage and advanced treatment decision-making. In this study we aimed to assess which factors potentially affect prehospital lactate levels.Methods: We performed a retrospective cohort study of all trauma patients attended by the Air Ambulance, Kent, Surrey &amp; Sussex (AAKSS) between July 2017 and April 2018 in whom a pre-hospital lactate was measured. Lactate was measured before AAKSS treatments were commenced, but generally after prehospital treatment by ground ambulance crews was initiated. Primary endpoint of interest was the association of various patient- and treatment characteristics with prehospital lactate levels. Results: During the study period, lactate was measured in 156 trauma patients. Median lactate was 3.0 [2.0-4.1] mmol/l. Patients with an elevated lactate more often had deranged indices of end organ perfusion- and oxygenation (shock index 0.80 [0.58-1.03] vs 0.61 [0.40-0.82], p &lt; 0.001, SpO2 96 [89-100%] vs 98 [96-100%], p = 0.025). They more often suffered from head injuries (62% vs 41%, p = 0.008), and received less analgesia prior to arrival of the AAKSS team (51.6% vs 67.2%, p = 0.03). In multivariate analysis, indices of end organ perfusion- and oxygenation only explained 15% of the variation in lactate levels. Conclusions: Prehospital lactate levels are not solely associated with indices of end organ perfusion- and oxygenation. Injury type, treatments given on scene and many other (unmeasured) factors likely play an important role as well. This should be taken into account when lactate is used in clinical algorithms to guide prehospital triage or treatment.</p

Determinants of prehospital lactate in trauma patients:A retrospective cohort study

Background: Point of care serum lactate measurement is emerging as an adjunct to prehospital clinical assessment and has the potential to guide triage and advanced treatment decision-making. In this study we aimed to assess which factors potentially affect prehospital lactate levels.Methods: We performed a retrospective cohort study of all trauma patients attended by the Air Ambulance, Kent, Surrey &amp; Sussex (AAKSS) between July 2017 and April 2018 in whom a pre-hospital lactate was measured. Lactate was measured before AAKSS treatments were commenced, but generally after prehospital treatment by ground ambulance crews was initiated. Primary endpoint of interest was the association of various patient- and treatment characteristics with prehospital lactate levels. Results: During the study period, lactate was measured in 156 trauma patients. Median lactate was 3.0 [2.0-4.1] mmol/l. Patients with an elevated lactate more often had deranged indices of end organ perfusion- and oxygenation (shock index 0.80 [0.58-1.03] vs 0.61 [0.40-0.82], p &lt; 0.001, SpO2 96 [89-100%] vs 98 [96-100%], p = 0.025). They more often suffered from head injuries (62% vs 41%, p = 0.008), and received less analgesia prior to arrival of the AAKSS team (51.6% vs 67.2%, p = 0.03). In multivariate analysis, indices of end organ perfusion- and oxygenation only explained 15% of the variation in lactate levels. Conclusions: Prehospital lactate levels are not solely associated with indices of end organ perfusion- and oxygenation. Injury type, treatments given on scene and many other (unmeasured) factors likely play an important role as well. This should be taken into account when lactate is used in clinical algorithms to guide prehospital triage or treatment.</p