The Effect of Operator Position on the Quality of Chest Compressions Delivered in a Simulated Ambulance.

BACKGROUND: Ambulances are where patient care is often initiated or maintained, but this setting poses safety risks for paramedics. Paramedics have found that in order to optimize patient care, they must compromise their own safety by standing unsecured in a moving ambulance. HYPOTHESIS/PROBLEM: This study sought to compare the quality of chest compressions in the two positions they can be delivered within an ambulance. METHODS: A randomized, counterbalanced study was carried out with 24 paramedic students. Simulated chest compressions were performed in a stationary ambulance on a cardiopulmonary resuscitation (CPR) manikin for two minutes from either: (A) an unsecured standing position, or (B) a seated secured position. Participants' attitudes toward the effectiveness of the two positions were evaluated. RESULTS: The mean total number of chest compressions was not significantly different standing unsecured (220; SD = 12) as compared to seated and secured (224; SD = 21). There was no significant difference in mean compression rate standing unsecured (110 compressions per minute; SD = 6) as compared to seated and secured (113 compressions per minute; SD = 10). Chest compressions performed in the unsecured standing position yielded a significantly greater mean depth (52 mm; SD = 6) than did seated secured (26 mm; SD = 7; P < .001). Additionally, the standing unsecured position produced a significantly higher percentage (83%; SD = 21) for the number of correct compressions, as compared to the seated secured position (8%; SD = 17; P < .001). Participants also believed that chest compressions delivered when standing were more effective than those delivered when seated. CONCLUSIONS: The quality of chest compressions delivered from a seated and secured position is inferior to those delivered from an unsecured standing position. There is a need to consider how training, technologies, and ambulance design can impact the quality of chest compressions.

Relationship between Segmental Dynamics Measured by Quasi-Elastic Neutron Scattering and Conductivity in Polymer Electrolytes.

Quasi-elastic neutron scattering experiments on mixtures of poly(ethylene oxide) and lithium bis(trifluoromethane)sulfonimide salt, a standard polymer electrolyte, led to the quantification of the effect of salt on segmental dynamics in the 1-10 Å length scale. The monomeric friction coefficient characterizing segmental dynamics on these length scales increases exponentially with salt concentration. More importantly, we find that this change in monomeric friction alone is responsible for all of the observed nonlinearity in the dependence of ionic conductivity on salt concentration. Our analysis leads to a surprisingly simple relationship between macroscopic ion transport in polymers and dynamics at monomeric length scales.

A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni.

Observations of binary stars containing an accreting black hole or neutron star often show x-ray emission extending to high energies (>10 kilo--electron volts), which is ascribed to an accretion disk corona of energetic particles akin to those seen in the solar corona. Despite their ubiquity, the physical conditions in accretion disk coronae remain poorly constrained. Using simultaneous infrared, optical, x-ray, and radio observations of the Galactic black hole system V404 Cygni, showing a rapid synchrotron cooling event in its 2015 outburst, we present a precise 461 ± 12 gauss magnetic field measurement in the corona. This measurement is substantially lower than previous estimates for such systems, providing constraints on physical models of accretion physics in black hole and neutron star binary systems.

Simultaneous conduction of electronic charge and lithium ions in block copolymers.

The main objective of this work is to study charge transport in mixtures of poly(3-hexylthiophene)-b-poly(ethylene oxide) (P3HT-PEO) block copolymers and lithium bis(trifluoromethanesulfonyl) imide salt (LiTFSI). The P3HT-rich microphase conducts electronic charge, while the PEO-rich microphase conducts ionic charge. The nearly symmetric P3HT-PEO copolymer used in this study self-assembles into a lamellar phase. In contrast, the morphologies of asymmetric copolymers with P3HT as the major component are dominated by nanofibrils. A combination of ac and dc impedance measurements was used to determine the electronic and ionic conductivities of our samples. The ionic conductivities of P3HT-PEO/LiTFSI mixtures are lower than those of mixtures of PEO homopolymer and LiTFSI, in agreement with published data obtained from other block copolymer/salt mixtures. In contrast, the electronic conductivities of the asymmetric P3HT-PEO copolymers are significantly higher than those of the P3HT homopolymer. This is unexpected because of the presence of the nonelectronically conducting PEO microphase. This implies that the intrinsic electronic conductivity of the P3HT microphase in P3HT-PEO copolymers is significantly higher than that of P3HT homopolymers.

Discontinuous Changes in Ionic Conductivity of a Block Copolymer Electrolyte through an Order-Disorder Transition.

The ionic conductivity of a block copolymer electrolyte was measured in an in situ small-angle X-ray scattering experiment as it transitioned from an ordered lamellar structure to a disordered phase. The ionic conductivity increases discontinuously as the electrolyte transitions from order to disorder. A simple framework for quantifying the magnitude of the discontinuity is presented. This study lays the groundwork for understanding the effect of more complex phase transitions such as order-order transitions on ion transport.

Current-induced formation of gradient crystals in block copolymer electrolytes.

Conventional ordered phases such as crystals and liquid crystals have constant domain spacings. In this Letter, we report on the formation of coherently ordered morphologies wherein the domain spacing changes continuously along a specified direction. We have coined the term "gradient crystal" to refer to this structure, a signature of which is a small-angle X-ray scattering pattern that resembles a sundial. Gradient crystals composed of a gyroid morphology form spontaneously when ionic current is driven through a block copolymer electrolyte. We propose that this structure forms because it allows for a continuous change in domain spacing without requiring the introduction of defects. Previous studies have shown that applied electric fields ranging from 1000 to 40,000 V/mm can induce long-range structural order, alignment, and morphological transitions in block copolymers. Gradient crystals form under applied electric fields as low as 2.5 V/mm due to the presence of direct ionic currents that are absent in the aforementioned studies.