Folded acoustic phonons in InAs-AlAs strained-layer superlattices
Raman spectroscopy is used to characterize highly mismatched (7%) InAs‐AlAs superlattices grown by atomic layer molecular beam epitaxy. In particular, folded acoustic modes are presented and compared with two different theoretical models (Rytov and linear chain). We find good agreement between theory and experiments. We estimate, with a simple model, the magnitude of the effect of the strain on the phonon frequency shifts.
Growth of CdS/ZnS strained layer superlattices on GaAs(0 0 1) by molecular-beam epitaxy with special reference to their structural properties and lattice dynamics
Abstract Strained layer CdS/ZnS superlattices have been grown on GaAs(0 0 1) by molecular-beam epitaxy using CdS and ZnS compound sources. The samples were investigated with special reference to their structural properties and lattice dynamics by means of X-ray diffraction and Raman spectroscopy. The results of four superlattices with different period length are discussed in detail. X-ray diffraction profiles show superlattice satellite peaks up to the fourth order indicating a high degree of periodicity. The lateral and in-depth homogeneity of the period length is also confirmed by Raman investigations. Folded longitudinal acoustic phonons in CdS/ZnS superlattices were observed for the first time. The experimental values agree very well with theoretical calculations based on the Rytov model and show the expected dependency on the superlattice period. The behaviour of the optical phonons is mainly determined by strain induced shifts caused by the high lattice mismatch (−7%) for this system. A good agreement between theoretical predictions and detected frequencies is obtained.
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.