1,084 research outputs found
Electron-phonon coupling in the conventional superconductor YNiBC at high phonon energies studied by time-of-flight neutron spectroscopy
We report an inelastic neutron scattering investigation of phonons with
energies up to 159 meV in the conventional superconductor YNiBC. Using
the SWEEP mode, a newly developed time-of-flight technique involving the
continuous rotation of a single crystal specimen, allowed us to measure a four
dimensional volume in (Q,E) space and, thus, determine the dispersion surface
and linewidths of the (~ 102 meV) and (~ 159 meV) type phonon
modes for the whole Brillouin zone. Despite of having linewidths of , modes do not strongly contribute to the total electron-phonon
coupling constant . However, experimental linewidths show a remarkable
agreement with ab-initio calculations over the complete phonon energy range
demonstrating the accuracy of such calculations in a rare comparison to a
comprehensive experimental data set.Comment: accepted for publication in PR
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A Spouted Bed Reactor Monitoring System for Particulate Nuclear Fuel
Conversion and coating of particle nuclear fuel is performed in spouted (fluidized) bed reactors. The reactor must be capable of operating at temperatures up to 2000°C in inert, flammable, and coating gas environments. The spouted bed reactor geometry is defined by a graphite retort with a 2.5 inch inside diameter, conical section with a 60° included angle, and a 4 mm gas inlet orifice diameter through which particles are removed from the reactor at the completion of each run. The particles may range from 200 µm to 2 mm in diameter. Maintaining optimal gas flow rates slightly above the minimum spouting velocity throughout the duration of each run is complicated by the variation of particle size and density as conversion and/or coating reactions proceed in addition to gas composition and temperature variations. In order to achieve uniform particle coating, prevent agglomeration of the particle bed, and monitor the reaction progress, a spouted bed monitoring system was developed. The monitoring system includes a high-sensitivity, low-response time differential pressure transducer paired with a signal processing, data acquisition, and process control unit which allows for real-time monitoring and control of the spouted bed reactor. The pressure transducer is mounted upstream of the spouted bed reactor gas inlet. The gas flow into the reactor induces motion of the particles in the bed and prevents the particles from draining from the reactor due to gravitational forces. Pressure fluctuations in the gas inlet stream are generated as the particles in the bed interact with the entering gas stream. The pressure fluctuations are produced by bulk movement of the bed, generation and movement of gas bubbles through the bed, and the individual motion of particles and particle subsets in the bed. The pressure fluctuations propagate upstream to the pressure transducer where they can be monitored. Pressure fluctuation, mean differential pressure, gas flow rate, reactor operating temperature data from the spouted bed monitoring system are used to determine the bed operating regime and monitor the particle characteristics. Tests have been conducted to determine the sensitivity of the monitoring system to the different operating regimes of the spouted particle bed. The pressure transducer signal response was monitored over a range of particle sizes and gas flow rates while holding bed height constant. During initial testing, the bed monitoring system successfully identified the spouting regime as well as when particles became interlocked and spouting ceased. The particle characterization capabilities of the bed monitoring system are currently being tested and refined. A feedback control module for the bed monitoring system is currently under development. The feedback control module will correlate changes in the bed response to changes in the particle characteristics and bed spouting regime resulting from the coating and/or conversion process. The feedback control module will then adjust the gas composition, gas flow rate, and run duration accordingly to maintain the bed in the desired spouting regime and produce optimally coated/converted particles
The effect of carbon dissemination on cost of equity
This study examines whether firms can influence their cost of equity (COE) by broadly disseminating their carbon information over Twitter. We study firms' dissemination decisions of carbon information by developing a comprehensive measure of carbon information that a firm makes on Twitter, referred to as iCarbon . Using a sample of 1,737 firm‐year observations for 584 nonfinancial firms with a Twitter account and listed on the U.S. NASDAQ stock exchange over the period 2009–2015, we find that iCarbon is significantly and negatively associated with COE. Our results are consistent after determining the effect of Bloomberg's environmental and environmental, social, and governance disclosure. The findings also hold when using alternative measures of COE and iCarbon
Strict dissipativity implies turnpike behavior for time-varying discrete time optimal control problems
Tunable Emergent Heterostructures in a Prototypical Correlated Metal
At the interface between two distinct materials desirable properties, such as
superconductivity, can be greatly enhanced, or entirely new functionalities may
emerge. Similar to in artificially engineered heterostructures, clean
functional interfaces alternatively exist in electronically textured bulk
materials. Electronic textures emerge spontaneously due to competing
atomic-scale interactions, the control of which, would enable a top-down
approach for designing tunable intrinsic heterostructures. This is particularly
attractive for correlated electron materials, where spontaneous
heterostructures strongly affect the interplay between charge and spin degrees
of freedom. Here we report high-resolution neutron spectroscopy on the
prototypical strongly-correlated metal CeRhIn5, revealing competition between
magnetic frustration and easy-axis anisotropy -- a well-established mechanism
for generating spontaneous superstructures. Because the observed easy-axis
anisotropy is field-induced and anomalously large, it can be controlled
efficiently with small magnetic fields. The resulting field-controlled magnetic
superstructure is closely tied to the formation of superconducting and
electronic nematic textures in CeRhIn5, suggesting that in-situ tunable
heterostructures can be realized in correlated electron materials
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