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Fracture of crystalline silicon (c-Si) solar cells in photovoltaic modules is a big concern to the photovoltaics (PV) industry. Cell cracks cause performance degradation and warranty issues to the manufacturers. The roots of cell fractures lie in the manufacturing and integration process of the cells and modules as they go through a series of elevated temperature and pressure processes, involving bonding of dissimilar materials, causing residual stresses. Evaluation of the exact physical mechanisms leading to these thermomechanical stresses is highly essential to quantify them and optimize the PV modules to address them. We present a novel synchrotron X-ray microdiffraction based techniques to characterize the stress and fracture in the crystalline silicon PV modules. We show the detailed stress state after soldering and lamination process, using the synchrotron X-ray microdiffraction experiments. We also calculate the maximum tolerable microcrack size in the c-Si cells to sustain the residual stress after lamination. We further demonstrate the effect of these residual stresses on the cell fractures using the widely accepted fracture (4-point bending) tests. These test results show that the soldering and lamination induced localized residual stresses indeed reduce the load-carrying capacity of the c-Si cells.
UK Biobank is a well-characterised cohort of over 500 000 participants that offers unique opportunities to investigate multiple diseases and risk factors.
An online mental health questionnaire completed by UK Biobank participants was expected to expand the potential for research into mental disorders.
An expert working group designed the questionnaire, using established measures where possible, and consulting with a patient group regarding acceptability. Case definitions were defined using operational criteria for lifetime depression, mania, anxiety disorder, psychotic-like experiences and self-harm, as well as current post-traumatic stress and alcohol use disorders.
157 366 completed online questionnaires were available by August 2017. Comparison of self-reported diagnosed mental disorder with a contemporary study shows a similar prevalence, despite respondents being of higher average socioeconomic status than the general population across a range of indicators. Thirty-five per cent (55 750) of participants had at least one defined syndrome, of which lifetime depression was the most common at 24% (37 434). There was extensive comorbidity among the syndromes. Mental disorders were associated with high neuroticism score, adverse life events and long-term illness; addiction and bipolar affective disorder in particular were associated with measures of deprivation.
The questionnaire represents a very large mental health survey in itself, and the results presented here show high face validity, although caution is needed owing to selection bias. Built into UK Biobank, these data intersect with other health data to offer unparalleled potential for crosscutting biomedical research involving mental health.
Declaration of interest
G.B. received grants from the National Institute for Health Research during the study; and support from Illumina Ltd. and the European Commission outside the submitted work. B.C. received grants from the Scottish Executive Chief Scientist Office and from The Dr Mortimer and Theresa Sackler Foundation during the study. C.S. received grants from the Medical Research Council and Wellcome Trust during the study, and is the Chief Scientist for UK Biobank. M.H. received grants from the Innovative Medicines Initiative via the RADAR-CNS programme and personal fees as an expert witness outside the submitted work.
A shape is called equable if its area and perimeter are numerically equal relative to some given system of units. For example, if a square is equable, then its side, a, must satisfy 4a = a2. So there is only one equable square, and it has side 4.
It is easy to investigate this idea for other shapes. Though not connected with this problem, the work of Imre Lakatos suggested a generalisation to us. Lakatos showed that Euler's classical formula V + F = E − 2 for polyhedra could be extended when the notion of tunnels was introduced .
The maple leafcutter moth (Paraclemensia acerifoliella (Fitch) (Lepidoptera: Incurvariidae) has been discovered in western Canada, feeding on saskatoon (Amelanchier alnifolia (Nuttall) Nuttall ex Roemer (Rosaceae)), a previously undocumented host. New records are detailed, and historical records are reviewed and assessed. Western populations are compared morphologically, genetically, and ecologically to populations feeding on maple (Acer Linnaeus; Sapindaceae) in eastern Canada. Paraclemensia Busck species host plants are discussed in relation to the hypothesised phylogenetic history of the genus. Although maple feeding is hypothesised to be the ancestral condition in the genus Paraclemensia, Rosaceae feeding (including Amelanchier) is hypothesised to be a derived capability of the P. acerifoliella species group.
A new Mo potential, developed recently by using an ab initio quantum mechanics theory, was used to study formation and time evolution of radiation defects, such as self-interstitial atoms (SIAs), vacancies, and small clusters of SIAs, using molecular dynamics (MD). MD models were developed for calculation of the diffusion coefficients of vacancies, self-interstitials, and small dislocation loops containing 2 to 37 SIAs; and the rate constants were calculated. Interactions of small SIA loops with SIAs were simulated. The results show that rotation of SIA from one <111> to another equivalent direction is an important mechanism that significantly contributes to kinetic coefficients.
Results for a radiolysis model sensitivity study of radiolytically produced H2O2 are presented as they relate to Spent (or Used) Light Water Reactor uranium oxide (UO2) nuclear fuel (UNF) oxidation in a low oxygen environment. The model builds on previous reaction kinetic studies to represent the radiolytic processes occurring at the nuclear fuel surface. Hydrogen peroxide (H2O2) is the dominant oxidant for spent nuclear fuel in an O2-depleted water environment. The most sensitive parameters have been identified with respect to predictions under typical conditions. As compared with the full model with about 100 reactions, it was found that only 30 to 40 of the reactions are required to determine [H2O2] to one part in 10–5 and to preserve most of the predictions for major species. This allows a systematic approach for model simplification and offers guidance in designing experiments for validation.
Structural materials in the new Generation IV reactors will operate in harsh radiation conditions coupled with high levels of hydrogen and helium production and will experience severe degradation of mechanical properties. Therefore, understanding of the physical mechanisms responsible for the microstructural evolution and corresponding mechanical property changes is critical. As the involved phenomena are very complex and span in several length scales, a multiscale approach is necessary in order to fully understand the degradation of materials in irradiated environments. In previous work, we used molecular dynamics simulations to develop critical rules for the mobility of dislocations in various iron alloys and their interaction with several types of defects that include, among others, helium bubbles and grain boundaries. In this work, Dislocation Dynamics simulations of iron alloys are used to study the mechanical behavior and the degradation under irradiation of large systems with high dislocation and defect densities.
Enhanced thermal conductivity oxide fuels offer increases in both safety and efficiency of commercial light water reactors. Low-temperature oxidative sintering and Spark Plasma Sintering (SPS) techniques have been used to produce UO2-SiC composite pellets. Oxidative sintering performed for 4 hours at 1200∼1600oC and SPS was employed only for 5 mins at the same temperature. While oxidative sintering failed to achieve enhanced thermal conductivity, the SPS sintered pellet obtained promising features such as higher density, better interfacial contact, and reduced chemical reaction. Thermal conductivity measurement at 100oC, 500oC, and 900oC revealed maximum 62% higher thermal conductivity value, when compared to UO2 pellets, in SPS sintered UO2-10vol% SiC composite pellet. The result shows that the SPS technique is required to sinter UO2-SiC nuclear fuel pellets with a high value of thermal conductivity.
Identical samples of uranium coupons were prepared and each exposed to hydrogen for different times (where this time is significantly less than a classically understood ‘induction time’). Samples were prepared from rolled depleted uranium stock: as-received oxide was removed on all surfaces and two faces (~12x12 mm) were polished to a sub-micron standard. Samples were individually taken through a Vacuum Thermal Pre-Treatment cycle from room temperature to 200°C to the reaction temperature (80°C) over 40 hours and subsequently exposed to 10 mbar O2 for 24 hours. After O2 was removed, the samples were exposed to hydrogen for pre-determined times of up to 48 minutes. Examination of the samples by Scanning Electron Microscopy (SEM) has, as expected, identified small features protruding from the surface believed to have been caused by sub-surface precipitation of UH3. In general these features are circular and isolated from each other, have a diameter of less than 3μm and appear as either ‘flat-topped’ or ‘domed’ morphology. In addition, longer time exposure samples show a predominance of ‘area attack’ where coalesced sub-surface precipitation appears to be confined to particular metal grains. X-Ray Diffraction (XRD) data show an increase in the quantity of UH3 with time.
Oxygen potentials of PuO2-x were measured at temperatures of 1473 - 1873 K by thermo-gravimetry. The oxygen potentials were determined by in situ analysis as functions of oxygen-to-metal ratio and temperature. The measurement data were analyzed on the basis of defect chemistry and an approximate equation was derived to represent the relationship among temperature, oxygen partial pressure, and deviation x in PuO2-x.
Two major causes of hardening and subsequent embrittlement in ferrite steels are the spinodal decomposition of the binary Fe-Cr solid solution and the carbide formation due to the presence of carbon as foreign interstitial atoms. In the present work, simulations of the microstructure evolution due to thermal ageing are performed by means of a kinetic Monte Carlo code and using a state-of-the-art interatomic potential based on density functional theory (DFT) predictions and experimental data. The main issues concern the possibility to perform thermal ageing simulations in an acceptable computational time frame and to reproduce a realistic behavior of carbon kinetics and carbide formation. The simulations on the binary system show the microstructural evolution during thermal ageing and allowed to find an exponential trend related to the acceleration as a function of temperature. With the insertion of carbon in the model, the chromium precipitation tends to accelerate. The carbon clustering, analyzed separately, is faster with higher C concentrations and in lattices with segregated chromium.
The electronic structure of delta plutonium (δ-Pu) and plutonium compounds is investigated using photoelectron spectroscopy (PES). Results for δ-Pu show a small component of the valence electronic structure which might reasonably be associated with a 5f6 configuration. PES results for PuTe are used as an indication for the 5f6 configuration due to the presence of atomic multiplet structure. Temperature dependent PES data on δ-Pu indicate a narrow peak centered 20 meV below the Fermi energy and 100 meV wide. The first PES data for PuCoIn5 indicate a 5f electronic structure more localized than the 5fs in the closely related PuCoGa5. There is support from the PES data for a description of Pu materials with an electronic configuration of 5f5 with some admixture of 5f6 as well as a localized/delocalized 5f5 description.
Nuclear fuels and materials present special problems to atomistic-scale modeling. At a metal-metal-oxide interface, the metal centers are charged on the oxide side, but neutral on the metallic side. The intimate contact necessitates that atomistic models for these materials be both compatible and consistent with one another at some level. A new "fragment’’ Hamiltonian (FH) model, at the atomistic level, is presented that reduces qualitatively to existing, successful models for metals, such as the embedded atom method, and ceramics, such as the charge equilibration models. Moreover, the FH model possesses both electron hopping and fundamental gaps that appear as separate terms in a generalized embedding function. The electron hopping contributions come from both one-electron and two-electron sources. These contributions appear as a result of the FH point of view, rather than being postulated. The model obeys certain wellknown theoretical limits that come from the nonlinearity of electron hopping processes as the volume of a crystal is changed. The generalized notion of embedding entails two variables instead of one. The ability to account for multiple charge states in the cations leads to the capability within the model to distinguish the qualitative differences among metallic, ionic, and covalent bonding environments. The details of all of these energies, among with fragmentfragment interactions, combine to determine the state of the atom in the material.