The frequency dependent response of the electrical impedance of UO2

AC impedance techniques in the frequency range 5 Hz to 5 MHz have been employed to measure dielectric properties of single crystal UO2 in the form of plate specimens. The dielectric constant has been measured down to 4 K, giving results consistent with previous reports. Both barrier and volume effects have been shown to contribute to the measured impedances. The barrier effects account for the anomalously large capacitances observed in previous attempts to measure the dielectric constant by the conventional plate technique. Activation energies for carriers in both boundary and bulk regions are similar (0.18 to 0.25 eV). The behaviour is consistent with the presence of electronic holes present in the concentrations to be expected from small deviations from stoichiometry

Electrical conductivity of polycrystalline uranium dioxide

The electrical impedance of a disc-shaped sample of polycrystalline UO2 has been measured over a frequency range of 10 Hz to 10 MHz at temperatures between 108 and 380 K. Three distinct regions in the impedance profiles were observed; these have been associated with the region near the metallic electrodes, with the bulk material and with the grain boundaries. Activation energies for conduction have been determined in each of the three regions [0.17, 0.13 and 0.29 eV for the electrode, bulk and grain boundary contributions, respectively]. The impedance response has been modelled using a two-phase microstructure and an effective medium treatment. At low temperatures the boundary region is less conducting than the grain interior. However, at ambient temperatures and above, the boundary region dominates and electrical conduction takes place primarily through the boundaries

The pressure dependence of the dielectric constant and electrical conductivity of single crystal uranium dioxide

Complex impedance techniques, within the frequency range 10 Hz to 1 MHz, have been used to make high pressure studies of monocrystalline uranium dioxide at ambient temperature. These techniques have shown that for frequencies below 40 MHz the electrical properties of high pressure samples are dominated by a boundary layer. The impedance methods have enabled us to make the first determination of the pressure dependence of the static dielectric constant of uranium dioxide within the boundary layer. The experimental pressure dependence (−0.03 kbar−1) is in reasonable agreement with that calculated (−0.02 kbar−1) using standard interatomic potentials. We have also measured the conductivity in the boundary layer as a function of pressure (2.5 μS kbar−1). The pressure dependences of the conductivity and the dielectric constant have been used to obtain an estimate of the carrier binding and hopping energies, which have then been compared with values predicted using the shell model

The electrical impedance of single-crystal urania at elevated temperatures

The electrical admittance of single-crystal urania has been measured from 300 to 1500 K, over a frequency range of 10 Hz to 10 MHz, using complex impedance spectroscopy. The data have been analyzed using a simple equivalent circuit of a parallel element comprising a conductance and a capacitance connected in series with a separate capacitance. The simple equivalent circuit also reanalyzes successfully the frequency dependence of the electrical conductivity found by Bates and his co-workers, giving results consistent with the present work. The conductance data show a distinct “kink” at about 1300 K, which is in good agreement with previous work, as are the activation energies: 0.12 eV (T 1300 K). Results are used to estimate the ambipolar contribution to the thermal conductivity above 1500 K

Implementing an Evidence-Based Practice Approach to Improve Communication of Delays to Patients and Family Members

Surgical procedures cause anxiety not only for the patient, but also for waiting family members. In order to improve the experience for those in the waiting room, it is important to reduce their anxiety and stress level. Enhancing perioperative communication can help reduce that anxiety. Effectiveness of that communication can have a direct impact on patient experience scores. For perioperative services, the patient experience indicator which addresses communication is Information provided about delays

Raising argument strength using negative evidence: A constraint on models of induction

Both intuitively, and according to similarity-based theories of induction, relevant evidence raises argument strength when it is positive and lowers it when it is negative. In three experiments, we tested the hypothesis that argument strength can actually increase when negative evidence is introduced. Two kinds of argument were compared through forced choice or sequential evaluation: single positive arguments (e.g., “Shostakovich’s music causes alpha waves in the brain; therefore, Bach’s music causes alpha waves in the brain”) and double mixed arguments (e.g., “Shostakovich’s music causes alpha waves in the brain, X’s music DOES NOT; therefore, Bach’s music causes alpha waves in the brain”). Negative evidence in the second premise lowered credence when it applied to an item X from the same subcategory (e.g., Haydn) and raised it when it applied to a different subcategory (e.g., AC/DC). The results constitute a new constraint on models of induction