Frequency dependence of electrical conductivity and dielectric constant of UO2

The dielectric constant and electrical conductivity of single crystal and polycrystalline UO2 are found to be frequency dependent. The dielectric constant measured at low frequencies is anomalously large at room temperature but decreases to a limiting value (~25) below about 130 K. A knee observed in the temperature dependence of the conductivity of polycrystalline UO2 corresponds to a process having an activation energy of 0.15 eV

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

The dielectric constant of UO2 below the Néel point

We report measurements of the frequency-dependent dielectric constant of UO2 from 4.2 K to above the phase transition at 30 K. The static dielectric constant of 23.6 at 4.2 K is comparable with accepted values at higher temperatures: it is essentially identical in both phases. The effects of undergoing the transition on the dielectric constant are marginal (about 1%) and take place in the temperature range 29 K to 37 K. The displacement of the oxygen sublattice, which occurs at the Ne´el point, should produce only a 0.05% change on the dielectric constant and of the opposite sense to that measured. Hence the structural changes at the transition are not the primary source of the observed small difference between the dielectric constant in the two phases which probably accrues from the influence of the displacements on a defect-related contribution

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

Informal carers' health-related quality of life and patient experience in primary care: evidence from 195,364 carers in England responding to a national survey.

BACKGROUND: We aim to describe the health-related quality of life of informal carers and their experiences of primary care. METHODS: Responses from the 2011-12 English General Practice Patient Survey, including 195,364 informal carers, were analysed using mixed effect logistic regressions controlling for age, gender, ethnicity and social deprivation to describe carer health-related quality of life (mobility, self-care, usual activities, pain, and anxiety/depression, measured using EQ-5D) and primary care experience (access, continuity and communication). RESULTS: Informal carers reported poorer health-related quality of life than non-carers of similar age, gender, ethnicity and social deprivation. Increasing caring commitment was associated with worse EQ-5D scores, with carers of 50+ hours a week scoring 0.05 points lower than non-carers (95 % CI 0.05 to 0.04), equivalent to 18 fewer days of full health annually. Considering each domain of EQ-5D separately, carers of 50+ hours/week were more likely to report pain OR = 1.53 (1.50-1.57), p < 0.0001, and anxiety/depression OR = 1.69 (1.66-1.73), p < 0.0001, than non-carers. Younger carers scored lower on EQ-5D than non-carer peers but the converse was true among over-85s. In the most deprived areas carers reported the equivalent of 37 fewer days of full health annually than carers in the most affluent areas. On average, carers reported poorer patient experiences in all areas of primary care than non-carers (odds ratios 0.84-0.97), with this difference being most marked in the domain of access. CONCLUSIONS: Informal carers experience a double disadvantage of poorer health-related quality of life and poorer patient experience in primary care. We find no evidence for health benefits of caregiving. We recommend physicians identify and treat carer health problems, including pain and anxiety/depression, particularly among young, deprived and high time-commitment carers. Improving patient experience for carers, including access to primary care, should be a priority.This is the final version of the article. It first appeared from BioMed Central via http://dx.doi.org/10.1186/s12875-015-0277-

Environmentally assisted fatigue crack nucleation in Ti-6Al-2Sn-4Zr-6Mo

An unexplained feature was observed at the fatigue crack origin of a number of alpha/beta titanium specimens tested at 450 °C in the low cycle fatigue regime. The origin was discoloured blue but this was not a result of temper colouration; this feature sometimes resulted in large reductions in fatigue lives. A number of specimens were examined to determine the cause and formation mechanism of these “blue spots.” This feature was associated with elevated oxygen and chloride levels and the presence of sodium. A mechanism based on hot-salt stress-corrosion cracking is proposed and the implications for service components are discussed

A developmentally regulated chaperone complex for the endoplasmic reticulum of male haploid germ cells

Glycoprotein folding is mediated by lectin-like chaperones and protein disulfide isomerases (PDIs) in the endoplasmic reticulum (ER). Calnexin and the PDI homologue ERp57 work together to help fold nascent polypeptides with glycans located toward the N-terminus of a protein, whereas PDI and BiP may engage proteins that lack glycans or have sugars toward the C-terminus. In this study, we show that the PDI homologue PDILT is expressed exclusively in post-meiotic male germ cells, in contrast to the ubiquitous expression of many other PDI family members in the testis. PDILT is induced during puberty and represents the first example of a PDI family member under developmental control. We find that PDILT is not active as an oxido-reductase, but interacts with the model peptide -somatostatin and nonnative BPTI in vitro, indicative of chaperone activity. In vivo, PDILT forms a tissue-specific chaperone complex with the calnexin homologue calmegin. The identification of a redox-inactive chaperone partnership defines a new system of testis-specific protein folding with implications for male fertility