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•Non-proportional loading paths imposed on nickel-based superalloy using crystal plasticity.•Potential mechanistic explanation for non-proportional detrimental effects in fatigue ...proposed.•Non-proportionality giving more slip activations, driving up GND and leading to shorter lives.
A dislocation and gradient-based crystal plasticity finite element study of fatigue has been carried out for nickel-based superalloy RR1000 in order to investigate detrimental non-proportional effects on fatigue life. Six differing multiaxial loading cycles including both proportional and non-proportional paths have been addressed and a critical stored energy density criterion employed for fatigue life. Non-proportional paths are shown to lead to higher numbers of intragranular slip system activations, reflecting experimental observations. These give higher geometrically necessary dislocation (GND) densities resulting from slip system interaction occurring through latent hardening effects in the model. The higher GND densities in turn drive up local stress and stored energy densities, thereby leading to lower predicted fatigue lives, in keeping with non-proportional fatigue experiments in the alloy considered. Intragranular slip system interaction may be the mechanistic explanation for non-proportional effects in fatigue of engineering alloys.
A non-local method for the establishment of geometrically necessary dislocation (GND) based on a non-local domain integral has been developed and incorporated into crystal plasticity finite element ...(CPFE) formulations. The proposed non-local GND method has been validated through a four-point bending case, where the mesh sensitivity of the traditional GND method has been substantially diminished by virtue of the applied non-local domain integral. A comprehensive parametric study has been conducted to investigate the non-local domain effect on the GND calculation. The application of the non-local GND method has resembled the experimental observation of the GND density distribution near a crack tip, and improved the stress field compared to the local method. The improvement on the accuracy of predicting a microstructural driving force at crack tips reveals the necessity of applying the non-local GND method in predicting material fatigue life.
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•A non-local method for finding geometrically necessary dislocation (GND) density has been developed.•The mesh sensitivity in conventional GND methods has been substantially diminished.•The application of the non-local GND method has captured the experimentally observed GND distribution near cracktip.
Abstract
Fatigue is a difficult multi-scale modelling problem nucleating from localised plasticity at the scale of dislocations and microstructure with significant engineering safety implications. ...Cold dwell fatigue is a phenomenon in titanium where stress holds at moderate temperatures lead to substantial reductions in cyclic life, and has been implicated in service failures. Using discrete dislocation plasticity modelling complemented by transmission electron microscopy, we successfully predict lifetimes for ‘worst case’ microstructures representative of jet engine spin tests. Fatigue loading above a threshold stress is found to produce slip in soft grains, leading to strong dislocation pile-ups at boundaries with hard grains. Pile-up stresses generated are high enough to nucleate hard grain basal dislocations, as observed experimentally. Reduction of applied cyclic load alongside a temperature excursion during the cycle lead to much lower densities of prism dislocations in soft grains and, sometimes, the elimination of basal dislocations in hard grains altogether.
During the late Silurian – Early Devonian there were significant changes in the biosphere and environment. However, there are few integrated studies of carbon and sulfur cycling in the Qujing Basin, ...in South China, which has extremely well-preserved sarcopterygian fossils. Here we report C-isotopic data of organic carbon (δ13Corg) and multiple S-isotopes of pyrite (δ34S and Δ33S) from two sections in the Qujing Basin. Our δ13Corg data show an increase of ~4‰ near the Silurian-Devonian boundary which can be correlated globally. We suggest that this rise in δ13Corg near the Silurian-Devonian boundary may have resulted from the weathering of the 13C-enriched carbonate platform, rather than from oceanic anoxia. This interpretation may explain why there is little evidence of a mass extinction near the Silurian-Devonian boundary in the Qujing Basin. Our S-isotopic data show positive δ34S values with either positive or negative Δ33S values, and most of the δ34S and Δ33S data can be explained by microbial sulfate reduction and Rayleigh distillation processes. The S-isotopic data from both sections suggest that seawater sulfate concentrations were very low in the Qujing Basin during the late Silurian – Early Devonian.
•High resolution δ13Corg records from the Xishancun and Dahe sections in the Qujing Basin.•First multiple S-isotope study of the sedimentary rocks across the Silurian-Devonian boundary.•Weathering of the 13C-enriched carbonate platform was responsible for the rise in δ13Corg.•Seawater sulfate concentrations were very low in the Qujing Basin.
Dislocation configurational energy and stored energy densities are determined in discrete dislocation and crystal plasticity modelling respectively and assessed with respect to experiments on single ...crystal nickel fatigue crack nucleation. Direct comparisons between the three techniques are provided for two crystal orientation fatigue tests. These provide confirmation that both quantities correctly identify the sites of fatigue crack nucleation and that stored energy density is a reasonable approximation to the more rigorous dislocation configurational energy. GND density is shown to be important in locating crack nucleation sites because of its role in the local configurational energy density.
•Integrated experimental and computational study of fatigue crack nucleation in two nickel single crystals using discrete dislocation plasticity and crystal plasticity.•Successful identification of the crack nucleation sites in both single crystals using the configurational energy density from discrete dislocation plasticity and the stored energy density from crystal plasticity.•GND density plays a significant role in the identification of crack nucleation sites at the micron length scale.•Microstructural quantities such as lattice rotation, principle stress, effective strain and SSD density cannot in their own right predict the crack initiation sites.
Throughout Earth history, large volcanic eruptions that inject sulfur-bearing gases are believed to have imparted strong forcings on global climates and ecosystems. Sulfur outgassing by the Siberian ...Traps Large Igneous Province (STLIP) is hypothesized to have catalyzed environmental catastrophe associated with the end-Permian extinction (EPE). However, there is as yet only sparse evidence for dispersal of atmospheric sulfate aerosols that precisely coincided with the EPE on land. Here we report S-isotopic compositions of pyrite (δ34S) from the Sydney Basin in SE Australia, where we find a sharp δ34S decrease from 0.04‰ to −21.52‰ coinciding with the stratigraphic level of the terrestrial extinction. The negative δ34S values in the extinction interval provide new evidence for a significant increase in atmospheric sulfate concentrations linked to fallout of sulfate aerosols originating from the Siberian Traps eruptions. We suggest that climatic perturbations of short-term cooling caused by the sulfate aerosols, along with longer-term global warming, and their interactions, may have contributed to the EPE on land. Our data suggest that sulfuric acid rain and ozone depletion may have greatly deteriorated global environments, leading to the terrestrial EPE.
•S-isotopic study on the end-Permian extinction in the Sydney Basin.•A sharp S-isotopic decrease coincides with the terrestrial extinction.•Climate changes due to sulfate aerosol loading contribute to the extinction.
Abstract
Continuous U(1) gauge symmetry, which guarantees the conservation of total excitations in linear bosonic systems, will be broken when it comes to the strong-coupling regime where the ...rotation wave approximation (RWA) fails. Here we develop analytic solutions for multi-mode bosonic systems with XX-type couplings beyond RWA, and propose a novel scheme to implement high-fidelity quantum state transfer (QST) and entanglement preparation (EP) with high speed. The scheme can be realized with designated coupling strength and pulse duration with which the excitation number keeps unchanged regardless of the breakdown of the global U(1) symmetry. In QST tasks, we consider several typical quantum states and demonstrate that this method is robust against thermal noise and imperfections of experimental sequence. In EP tasks, the scheme is successfully implemented for the preparation of Bell states and W-type states, within a shortest preparation time.
The Songliao Basin, with an area of ~260,000 km2 in northeast China, hosts the largest oilfield in China, which is one of the world's most productive oilfields. However, the origin of the ...organic-rich upper Cretaceous source rocks remains controversial. In this study, we report multiple S-isotopic compositions of pyrite (δ34S and Δ33S) from Member 1 (K2n1) and Member 2 (K2n2) of the Nenjiang Formation in the Songliao Basin. Our isotopic results reveal an extraordinarily large negative δ34S excursion of 50.54‰ (from +11.09‰ to −39.45‰), which is strong evidence for seawater incursions. The increasing positive Δ33S excursion coupled with the negative δ34S excursion strengthen the inference of a large influx of seawater to the Songliao Basin. We used a steady-state isotope box model to estimate the magnitude of the seawater incursions. Our modeling results show that the sulfate concentrations may have increased by 12–46 times when seawater invaded the Songliao Basin. We suggest that marine incursions may have facilitated the chemical stratification of the Songliao Basin and played an important role in the formation of the oil source rocks. Our findings potentially have important implications for understanding the formation of oilfields elsewhere.
•Multiple S-isotopic study on the seawater incursion events in the Songliao Basin.•Negative δ34S and positive Δ33S of pyrite support the hypothesis that marine incursions occurred.•A box model to estimate the magnitude of the seawater incursions.•Marine incursions may have facilitated the formation of the organic-rich source rocks.
Lipid metabolism has a profound impact on gastric cancer (GC) progression and is a newly targetable vulnerability for cancer therapy. Given the importance of lipids in cancer cellular processes, in ...this study we employed lipidomic clinical and transcriptomic data to connect the variations of lipid metabolism changes of GC. We constructed a clinical nomogram based on the lipid factors and other clinical items. Then by using multi-omics techniques, we established a lipid-related gene signature for individualized prognosis prediction in patients with GC. Moreover, a total of 1357 GC cases were then applied to evaluate the robustness of this model. WGCNA was used to identify co-expression modules and enriched genes associated with GC lipid metabolism. The role of key genes ACLY in GC was further investigated. The prognostic value of the lipgenesis signature was analyzed using Cox regression model, and clinical nomogram was established. Among them, we observed overexpression of ACLY significantly increased the levels of intracellular free fatty acid and triglyceride, and activated AKT/mTOR pathway to promote cancer development. In conclusion, our findings revealed that GC exhibited a reprogramming of lipid metabolism in association with an altered expression of associated genes. Among them, ACLY significantly promoted GC lipid metabolism and increased cancer cell proliferation, suggesting that this pathway can be targetable as a metabolic vulnerability in future GC therapy.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The end-Permian mass extinction (EPME) was the most severe extinction event in the past 540 million years, and the Siberian Traps large igneous province (STLIP) is widely hypothesized to have been ...the primary trigger for the environmental catastrophe. The killing mechanisms depend critically on the nature of volatiles ejected during STLIP eruptions, initiating about 300 kyr before the extinction event, because the atmosphere is the primary interface between magmatism and extinction. Here we report Ni isotopes for Permian-Triassic sedimentary rocks from Arctic Canada. The δ
Ni data range from -1.09‰ to 0.35‰, and exhibit the lightest δ
Ni compositions ever reported for sedimentary rocks. Our results provide strong evidence for global dispersion and loading of Ni-rich aerosol particles into the Panthalassic Ocean. Our data demonstrate that environmental degradation had begun well before the extinction event and provide a link between global dispersion of Ni-rich aerosols, ocean chemistry changes, and the EPME.
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