Thermally Driven Electronic Topological Transition in FeTi.

Ab initio molecular dynamics, supported by inelastic neutron scattering and nuclear resonant inelastic x-ray scattering, showed an anomalous thermal softening of the M_{5}^{-} phonon mode in B2-ordered FeTi that could not be explained by phonon-phonon interactions or electron-phonon interactions calculated at low temperatures. A computational investigation showed that the Fermi surface undergoes a novel thermally driven electronic topological transition, in which new features of the Fermi surface arise at elevated temperatures. The thermally induced electronic topological transition causes an increased electronic screening for the atom displacements in the M_{5}^{-} phonon mode and an adiabatic electron-phonon interaction with an unusual temperature dependence.

Temperature dependent magnon-phonon coupling in bcc Fe from theory and experiment.

An ab initio based framework for quantitatively assessing the phonon contribution due to magnon-phonon interactions and lattice expansion is developed. The theoretical results for bcc Fe are in very good agreement with high-quality phonon frequency measurements. For some phonon branches, the magnon-phonon interaction is an order of magnitude larger than the phonon shift due to lattice expansion, demonstrating the strong impact of magnetic short-range order even significantly above the Curie temperature. The framework closes the previous simulation gap between the ferro- and paramagnetic limits.

Positive vibrational entropy of chemical ordering in FeV.

Inelastic neutron scattering and nuclear resonant inelastic x-ray scattering were used to measure phonon spectra of FeV as a B2 ordered compound and as a bcc solid solution. The two data sets were combined to give an accurate phonon density of states, and the phonon partial densities of states for V and Fe atoms. Contrary to the behavior of ordering alloys studied to date, the phonons in the B2 ordered phase are softer than in the solid solution. Ordering increases the vibrational entropy by +0.22±0.03 kB/atom, which stabilizes the ordered phase to higher temperatures. First-principles calculations show that the number of electronic states at the Fermi level increases upon ordering, enhancing the screening between ions, and reducing the interatomic force constants. The effect of screening is larger at the V atomic sites than at the Fe atomic sites.

Comparison of two systems for quality assurance of prehospital advanced life support services.

INTRODUCTION: The need for quality assurance (QA) systems for review of prehospital advanced life support (ALS) care has long been recognized. However, there only have been limited published studies on the operation and cost of QA systems for prehospital care. A number of different systems currently are in use, and the relative effectiveness of different QA systems has not been well determined. OBJECTIVE: The aim of this study was to compare the personnel work-time and costs of two different systems of QA for prehospital ALS services, and thereby determine which type of system was more cost-effective in the generation of QA reports. METHODS: The quality assurance program (System 1) for three independent ALS services in a rural/suburban area and the QA program (System 2) for a nearby urban ALS service were compared. Data recorded included the training level and number of hours per year devoted exclusively to QA activities by different personnel. The annual costs for other aspects of the QA systems and apportioned salary costs for time spent on QA work were recorded. RESULTS: System 1, a computer-based system, utilized 1,116 hours per year of personnel time and required [US]$17,662 in total costs per year (average cost per run reviewed of $4.38). System 2 (a manual system) utilized 569 hours per year of personnel time and had an annual cost of [US]$8,361 (or $2.15 per run reviewed). System 1 generated 852 reports per year (21% of runs) about non-compliance with protocols or charting deficiencies. System 2 generated 284 reports per year (7.3% of runs) for similar events. CONCLUSIONS: Either a computer-based or "manual" system for QA of prehospital ALS services can be utilized. A computer-based system requires more personnel time and is more expensive, but generates more reports per year than does the manual system. A computer-based system more readily can retrieve run report data for further review.

Pressure-Induced Invar Behavior in Pd3Fe.

Synchrotron x-ray diffraction (XRD) measurements, nuclear forward scattering (NFS) measurements, and density functional theory (DFT) calculations were performed on L1_{2}-ordered Pd3Fe. Measurements were performed at 300 K at pressures up to 33 GPa, and at 7 GPa at temperatures up to 650 K. The NFS revealed a collapse of the 57Fe magnetic moment between 8.9 and 12.3 GPa at 300 K, coinciding with a transition in bulk modulus found by XRD. Heating the sample under a pressure of 7 GPa showed negligible thermal expansion from 300 to 523 K, demonstrating Invar behavior. Zero-temperature DFT calculations identified a ferromagnetic ground state and showed several antiferromagnetic states had comparable energies at pressures above 20 GPa.