409 research outputs found
Time Dependent Effects and Transport Evidence for Phase Separation in La_{0.5}Ca_{0.5}MnO_{3}
The ground state of La_{1-x}Ca_{x}MnO_{3} changes from a ferromagnetic
metallic to an antiferromagnetic charge-ordered state as a function of Ca
concentration at x ~ 0.50. We present evidence from transport measurements on a
sample with x = 0.50 that the two phases can coexist, in agreement with other
observations of phase separation in these materials. We also observe that, by
applying and then removing a magnetic field to the mainly charge-ordered state
at some temperatures, we can "magnetically anneal" the charge order, resulting
in a higher zero-field resistivity. We also observe logarithmic time dependence
in both resistivity and magnetization after a field sweep at low temperatures.Comment: 9 pages, LATEX, 3 postscript figure
Superconductivity and Antiferromagnetism: Hybridization Impurities in a Two-Band Spin-Gapped Electron System
We present the exact solution of a one-dimensional model of a spin-gapped
correlated electron system with hybridization impurities exhibiting both
magnetic and mixed-valence properties. The host supports superconducting
fluctuations, with a spin gap. The localized electrons create a band of
antiferromagnetic spin excitations inside the gap for concentrations x of the
impurities below some critical value x_c. When x = x_c the spin gap closes and
a ferrimagnetic phase appears. This is the first example of an exactly solvable
model with coexisting superconducting and antiferromagnetic fluctuations which
in addition supports a quantum phase transition to a (compensated)
ferrimagnetic phase. We discuss the possible relevance of our results for
experimental systems, in particular the U-based heavy-fermion materials.Comment: 4 page
Limit-(quasi)periodic point sets as quasicrystals with p-adic internal spaces
Model sets (or cut and project sets) provide a familiar and commonly used
method of constructing and studying nonperiodic point sets. Here we extend this
method to situations where the internal spaces are no longer Euclidean, but
instead spaces with p-adic topologies or even with mixed Euclidean/p-adic
topologies.
We show that a number of well known tilings precisely fit this form,
including the chair tiling and the Robinson square tilings. Thus the scope of
the cut and project formalism is considerably larger than is usually supposed.
Applying the powerful consequences of model sets we derive the diffractive
nature of these tilings.Comment: 11 pages, 2 figures; dedicated to Peter Kramer on the occasion of his
65th birthda
Thermally activated exchange narrowing of the Gd3+ ESR fine structure in a single crystal of Ce1-xGdxFe4P12 (x = 0.001) skutterudite
We report electron spin resonance (ESR) measurements in the Gd3+ doped
semiconducting filled skutterudite compound Ce1-xGdxFe4P12 (x = 0.001). As the
temperature T varies from T = 150 K to T = 165 K, the Gd3+ ESR fine and
hyperfine structures coalesce into a broad inhomogeneous single resonance. At T
= 200 K the line narrows and as T increases further, the resonance becomes
homogeneous with a thermal broadening of 1.1(2) Oe/K. These results suggest
that the origin of these features may be associated to a subtle interdependence
of thermally activated mechanisms that combine: i) an increase with T of the
density of activated conduction-carriers across the T-dependent semiconducting
pseudogap; ii) the Gd3+ Korringa relaxation process due to an exchange
interaction, J_{fd}S.s, between the Gd3+ localized magnetic moments and the
thermally activated conduction-carriers and; iii) a relatively weak confining
potential of the rare-earth ions inside the oversized (Fe2P3)4 cage, which
allows the rare-earths to become rattler Einstein oscillators above T = 148 K.
We argue that the rattling of the Gd3+ ions, via a motional narrowing
mechanism, also contributes to the coalescence of the ESR fine and hyperfine
structure.Comment: 7 pages, 9 figures, accepted for publication in Phys Rev
Status of Simulation-Based Training in Departments of Surgery in the United States
Background: Surgical simulation is particularly attractive because it allows training in a safe, controlled, and standardized environment. However, the status of surgical simulation among Departments of Surgery (DoS) in the United States is unknown. The objective of this study was to characterize the status of simulation-based training in DoS in the United States. Materials and methods: A Qualtrics online survey was sent to 177 chairs of DoS in the United States in March 2018 regarding the utilization of surgical simulation in their department. Questions in the survey were focused on simulation capacities and activities as well as chairs' perception of the value and purpose of simulation. Results: A total of 87 of 177 chairs responded to the survey (49% response rate). Most programs had either 20-50 trainees (42 of 87; 48%) or more than 50 trainees (37 of 87; 43%). Most chairs reported having a simulation center in their institution (85 of 87; 98%) or department (60 of 86; 70%) with a formal simulation curriculum for their trainees (83 of 87; 95%). Ninety percent (78 of 87) of DoS had protected time for simulation education for their residents, with most residents engaging in activities weekly or monthly (65 of 85; 76%). Although most chairs felt simulation improves patient safety (72 of 84; 86%) and is useful for practicing surgeons (68 of 84; 81%), only 40% reported that faculty use simulation to maintain technical skills and only 17% reported that faculty use simulation to address high complication rates. Conclusions: The vast majority of the DoS in the United States have established simulation activities for their trainees. However, engagement of faculty in simulation to maintain or improve their skills remains low
Electrical transport properties of single-crystal CaB6, SrB6, and BaB6
The electrical resistivity and Hall effect of alkaline-earth-metal hexaboride single crystals are measured as a function of temperature, hydrostatic pressure, and magnetic field. The transport properties vary weakly with the external parameters and are modeled in terms of intrinsic variable-valence defects. These defects can stay either in (1) delocalized shallow levels or in (2) localized levels resonant with the conduction band, which can be neutral or negatively charged. Satisfactory agreement is obtained for electronic transport properties in a broad temperature and pressure range, although fitting the magnetoresistance is less straightforward and a combination of various mechanisms is needed to explain the field and temperature dependences.We acknowledge support from Grant No. MAT2012-38213-C02-01 from the Ministerio de EconomĂa y Competividad of Spain. Additional support from Diputacion General de Aragon (DGA-CAMRADS) is also acknowledged. Work at Los Alamos was performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences,
Division of Materials Science and Engineering. P.F.S.R. acknowledges a Director’s Postdoctoral Fellowship through the LANL LDRD program. P.S. acknowledges the support by the U.S. Department of Energy (BES) under Grant No. DE-FG02-98ER45707.Peer Reviewe
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We wish to thank Manyozo et al for their comments. We agree that police data tend to underreport injuries and death due to poor traffic police response and follow up on injured victims (e.g. fatalities on route or upon arrival to the hospital)
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