Anomalous behavior of nonequilibrium excitations in UO2

Abstract

Ultrafast optical pump-probe studies of uranium dioxide (UO 2) under pressure were performed in order to better understand the material's response to ionizing radiation. Photoexcitation generates oscillations in the time-resolved reflectivity at two distinct GHz-scale frequencies. The higher frequency mode is attributed to a coherent longitudinal acoustic mode. The lower frequency mode does not correspond to any known excitation under equilibrium conditions. The frequency and lifetime of the low-frequency mode are studied as a function of pressure. Abrupt changes in the pressure-dependent slopes of these attributes are observed at ~10 GPa, which correlates with an electronic transition in UO 2. Variation of probe wavelength reveals that the low k dispersion of the low-frequency mode does not fit into either an optical or acoustic framework. Rather, we propose that this mode is related to the dynamical magnetic structure of UO 2. The implications of these results help account for the anomalously small volume of damage known to be caused by ionizing radiation in UO 2 ; we propose that the existence of the low-frequency mode enhances the material's transient thermal conductivity, while its long lifetime lengthens the timescale over which energy is dissipated. Both mechanisms enhance damage recovery.

The Economics of Wastewater Treatment Decentralization: A Techno-economic Evaluation

“… Recovering nitrogen could reduce the production of artificial fertilizers via the Haber–Bosch process, which fixes nitrogen from the air but uses up to 2% of the world’s energy and represents 50% of the energy in European agriculture The energy demand to run aeration blowers in the aeration-based AS process accounts for more than 50–75% of the net power demand in wastewater treatment plants (WWTPs) needed to meet the mandated amount of dissolved oxygen. − Source separation and decentralization could reduce the current increase in energy demand (and concurrent carbon footprint) caused by the implementation of new technologies that achieve higher effluent quality at the expense of higher energy demand by producing renewable energy in useful forms (heat, methane) and by avoiding energy-demanding AS processes and transport − The current trend in clean decentralized energy (i.e., biogas, solar, wind) offers new possibilities of decentralized wastewater treatment, making new water reuse systems scalable, off-grid, and without the need for the transport of fossil fuels. − Vacuum toilets, as a way of source separation, can reduce BW water consumption by 90% to 35 L per person/day. ,− , and the overall consumption by about 25% The treatment alternatives can increase the ability of urban wastewater systems to adapt as a response to change and enhance climate-resilient infrastructures. ,− …”

“…Source separation and decentralization could reduce the current increase in energy demand (and concurrent carbon footprint) caused by the implementation of new technologies that achieve higher effluent quality at the expense of higher energy demand by producing renewable energy in useful forms (heat, methane) and by avoiding energy-demanding AS processes and transport − …”