Three-Dimensional Characterization of Superdislocation Interactions in the High Temperature and Low Stress Creep Regime of Ni-Base Superalloy Single Crystals
Monocrystaline Ni-base superalloys are the material of choice for first row blades in jet engine gas turbines. Using a novel visualization tool for 3D reconstruction and visualization of dislocation line segments from stereo-pairs of scanning transmission electron microscopies, the superdislocation substructures in Ni-base superalloy LEK 94 (crept to e = 26%) are characterized. Probable scenarios are discussed, how these dislocation substructures form.
On the nature of γ′ phase cutting and its effect on high temperature and low stress creep anisotropy of Ni-base single crystal superalloys
Abstract The creep anisotropy of the single crystal superalloy LEK 94 deformed in tension along [0 0 1] and [1 1 0] directions at 1293 K and 160 MPa was investigated. Elementary microstructural processes which are responsible for a higher increase in creep rates with strain during [1 1 0] as compared to [0 0 1] tensile loading were identified. [1 1 0] tensile creep is associated with a higher number of γ′ phase cutting events, where two dislocations with equal Burgers vectors of type 〈1 1 0〉 jointly shear the γ′ phase. The resulting 〈2 2 0〉-type superdislocation can move by glide. In contrast, during [0 0 1] tensile loading, two dislocations with different 〈1 1 0〉-type Burgers vectors must combine for γ′ phase cutting. The resulting 〈2 0 0〉-type superdislocations can only move by a combination of glide and climb. The evolution of dislocation networks during creep determines the nature of the γ′ phase cutting events. The higher [1 1 0] creep rates at strains exceeding 2% result from a combination of a higher number of cutting events (density of mobile dislocations in γ′) and a higher superdislocation mobility (〈2 2 0〉 glide) in the γ′ phase.
Expected annual emergency miles per ambulance: an indicator for measuring availability of Emergency Medical Services resources.
CONTEXT
To ensure equitable access to prehospital care, as recommended by the Rural and Frontier Emergency Medical Services (EMS) Agenda for the Future, policymakers will need a uniform measure of EMS infrastructure.


PURPOSE AND METHODS
This paper proposes a county-level indicator of EMS resource availability that takes into consideration existing EMS resources (ambulances), population health and demographics, and geographic factors. The indicator, the EXpected annual emergency miles per AMBulance (EXAMB), provides a basis for comparing ambulance availability across counties within states. A method for calculating the EXAMB indicator is demonstrated using data from 5 states.


FINDINGS
The EXAMB indicator was negatively correlated with ambulance availability per 100,000 population in 4 of the 5 states in the study. The indicator was positively correlated with rurality in 3 states. In Mississippi, South Carolina, and Wyoming, whole-county health professional shortage areas had median EXAMB values 45%-81% higher than those of the non-health professional shortage areas counties.


CONCLUSIONS
Future research should explore the relationship of the EXAMB to EMS outcomes, with the ultimate goal of developing a nationally recognized indicator of "adequate" EMS resource availability.