An experimental study is described on the fracture toughness and micro-mechanisms associated with the initiation and propagation of cracks in metallic nickel containing marked gradients in grain size, ranging from ∼30 nm to ∼4 μm. Specifically, cracks are grown in a gradient structured (GS) nickel with grain-size gradient ranging from the coarse macro-scale to nano-scale (CG → NG) and vice versa (NG → CG), with the measured crack-resistance R-curves compared to the corresponding behavior in uniform nano-grained (NG) and coarse-grained (CG) materials. It is found that the gradient structures display a much-improved combination of high strength and toughness compared to uniform grain-sized materials. However, based on J-integral measurements in the gradient materials, the crack-initiation toughness is far higher for cracks grown in the direction of the coarse-to-nano grained gradient than vice versa, a result which we ascribe primarily to excessive crack-tip blunting in the coarse-grained microstructure. Both gradient structures, however, display marked rising R-curve behavior with exceptional crack-growth toughnesses exceeding 200 MPa.m½.

Lithium-ion batteries (LIBs) commercially dominate portable energy storage and have been extended to hybrid/electric vehicles by utilizing electrode materials with enhanced energy density. However, the energy density and cycling life of LIBs must extend beyond the current reach of commercial electrodes to meet the performance requirements for transportation applications. Carbon-based anodes, serving as the main negative electrodes in LIBs, have an intrinsic capacity limitation due to the intercalation mechanism. Some nanostructured carbon materials offer very interesting reversible capacities and can be considered as future anode materials. However, their fabrication processes are often complicated and expensive. Theoretically, using a lithium metal anode is the best way of delivering high energy density due to its largest theoretical capacity of more than 3800 mAh g^-1; however, lithium metal is highly reactive with liquid electrolytes. Alternative anodes are being explored, including other lithium-reactive metals, such as Si, Ge, Zn, V, and so forth. These metals react reversibly with a large amount of Li per formula unit to form lithium-metal alloys, rendering these materials promising candidates for next-generation LIBs with high energy density. Though, most of these pure metallic anodes experience large volume changes during lithiation and delithiation processes that often results in cracking of the anode material and a loss electrical contact between the particles. Nanosized metal sulfides were recently found to possess better cycling stability and larger reversible capacities over pure metals. Further improvements and developments of metal sulfide-based anodes rely on a fundamental understanding of their electrochemical cycling mechanisms. Not only must the specific electrochemical reactions be correctly identified, but also the microstructural evolution upon electrochemical cycling, which often dictates the cyclability and stability of nanomaterials in batteries, must be clearly understood. Probing these dynamic evolution processes, i.e. the lithiation reactions and morphology evolutions, are often challenging. It requires both high-resolution chemical analysis and microstructural identification. In situ transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS) has recently been raised as one of the most powerful techniques for monitoring electrochemical processes in anode materials for LIBs. In this work, we focus on elucidating the origin of the structural stability of SnS₂ during electrochemical cycling by revealing the microstructural evolution of SnS₂ upon lithiation using in situ TEM. Crystalline SnS₂ was observed to undergo a two-step reaction after the initial lithium intercalation: (1) irreversible formation of metallic tin and amorphous lithium sulfide and (2) reversible transformation of metallic tin to Li-Sn alloys, which is determined to be the rate-determining step. More interestingly, it was discovered that a self-assembled composite framework formed during the irreversible conversion reaction, which has not been previously reported. Crystalline Sn nanoparticles are well arranged within an amorphous Li₂S "matrix" in this self-assembled framework. This nanoscale framework confines the locations of individual Sn nanoparticles and prevents particle agglomeration during the subsequent cycling processes, therefore providing desired structural tolerance and warranting a sufficientelectron pathway. Our results not only explain the outstanding cycling stability of SnS₂ over metallic tin anodes, but also provide important mechanistic insights into the design of high-performance electrodes for next-generation LIBs through the integration of a unique nanoframework.

The efficacy and safety of combining open-configuration magnetic resonance imaging (MRI) and an optical surgical navigation system (OSNS) for guidance of percutaneous liver cryoablation were evaluated in a pig model. This approach was successfully executed in eight test pigs under general anesthesia. Another two pigs spared from ablation served as controls. MRI studies, blood testing, and pathologic examinations were performed at various time points. MRI-determined minimal and maximal cryolesion diameters were 19.4 ± 1.5 mm and 44.3 ± 1.8 mm, respectively (mean volume, 8.32 ± 2.41 cm³). The lesions were readily visible by MRI on postablation Days 2 and 7, all presenting as teardrop-shaped regions of low signal intensity in T1-weighted images and high signal intensity in T2-weighted images. Mean serum alanine aminotransferase concentration transiently increased postablation, and mean blood platelet count transiently declined (both, P < 0.05). The mean necrotic tissue volume generated by pathologic assessment was less than that determined by MRI (4.24 ± 2.3 cm³ vs. 8.32 ± 2.41 cm³, P < 0.05). Cell necrosis isotherms in MRI views were within 6.0 ± 0.8 mm of cryolesion edges. Inflammatory cell infiltrates and exuberant granulation tissue surrounded necrotic areas on postablation Day 7. Combined open-configuration MRI and OSNS guidance of percutaneous liver cryoablation proved effective and safe in our animal model. This concept seems ideal for precision image-guided hepatic ablation in a clinical setting.

Background

As a recently discovered member of the DPANN superphylum, Woesearchaeota account for a wide diversity of 16S rRNA gene sequences, but their ecology, evolution, and metabolism remain largely unknown.

Results

Here, we assembled 133 global clone libraries/studies and 19 publicly available genomes to profile these patterns for Woesearchaeota. Phylogenetic analysis shows a high diversity with 26 proposed subgroups for this recently discovered archaeal phylum, which are widely distributed in different biotopes but primarily in inland anoxic environments. Ecological patterns analysis and ancestor state reconstruction for specific subgroups reveal that oxic status of the environments is the key factor driving the distribution and evolutionary diversity of Woesearchaeota. A selective distribution to different biotopes and an adaptive colonization from anoxic to oxic environments can be proposed and supported by evidence of the presence of ferredoxin-dependent pathways in the genomes only from anoxic biotopes but not from oxic biotopes. Metabolic reconstructions support an anaerobic heterotrophic lifestyle with conspicuous metabolic deficiencies, suggesting the requirement for metabolic complementarity with other microbes. Both lineage abundance distribution and co-occurrence network analyses across diverse biotopes confirmed metabolic complementation and revealed a potential syntrophic relationship between Woesearchaeota and methanogens, which is supported by metabolic modeling. If correct, Woesearchaeota may impact methanogenesis in inland ecosystems.

Conclusions

The findings provide an ecological and evolutionary framework for Woesearchaeota at a global scale and indicate their potential ecological roles, especially in methanogenesis.