Barre granite exhibits strong anisotropy due to its pre-existing microcracks induced by long-term tectonic loading. The quantification of rock anisotropy in fracture properties such as mode-I ...fracture toughness under a wide range of loading rates is critical to a variety of rock engineering applications. To quantify fracture toughness of Barre granite, notched semi-circular bend (NSCB) fracture tests are conducted statically with an MTS hydraulic servo-control testing machine and dynamically with a split Hopkinson pressure bar (SHPB) system. Barre granite samples are prepared based on the three principal directions, resulting in six orientation sample groups. For dynamic tests, pulse shaping technique is used to achieve dynamic force balance. The finite element method is then implemented to formulate equations relating the failure load to the mode-I fracture toughness using an orthotropic elastic material model. For samples in the same orientation group, the fracture toughness shows clear loading rate dependence, with the fracture toughness increasing with the loading rate. The fracture toughness anisotropy is characterized by the ratio of the largest fracture toughness over the smallest one at a given loading rate. The mode-I fracture toughness anisotropy exhibits a pronounced rate dependence, being strong under static loading while diminishing as the loading rate increases. The mode-I fracture toughness anisotropy may be understood by considering the preferentially oriented microcracks, which will be fully explored in the future.
► Used the ISRM standard to investigate the dynamic fracture toughness of Barre granite. ► Shaped the loading pulse in SHPB tests to achieve dynamic force balance. ► Developed formulas to determine rock fracture toughness for orthotropic elastic material. ► Quantified both static and dynamic fracture toughness anisotropy of Barre granite. ► Demonstrated rate dependence of the fracture toughness anisotropy of Barre granite.
Systematic variations of the exposure time and point distance of the pulsed laser used in selective laser melting (SLM) of Ti-6Al-4V resulted in three representative microstructures: the fully ...martensitic α', the near-α' containing a small amount of isolated β, and the fully lamellar α/β. The energy density in SLM determines the steady-state temperature in a deposited layer reached by balance between heat input from the subsequent layers and heat loss into the previous ones. A critical energy density was revealed below which no in-situ α' decomposition occurred. On the other hand, the in-situ formation of fully lamellar α/β was obtained using energy density higher than this critical value, leading to a steady-state temperature above that for α' decomposition for a sufficiently long duration. All three microstructures exhibited high tensile yield strength of 1100–1150 MPa, with excellent tensile elongation in the fully martensitic α' (~15%) and fully lamellar α/β (~12%) but significantly lower ductility in the near-α' (< 6%). The best ductility observed in the fully martensitic alloy dismisses the myth that α' is inherently brittle. Instead, the brittleness in the near-α' alloy can be attributed to the presence of thin β lamellae on the primary α' plates oriented at ~45° to the tensile axis, causing substantial stress concentration at the α/β interface.
•The full displacement and strain fields are measured using DIC.•The history of dynamic stress intensity factor of rocks is determined.•The effect of loading rate on dynamic fracture properties is ...characterized.•Dependence of fracture propagation toughness on fracture velocity is obtained.
Loading rate is the main controlling factor in dynamic failure of rocks. In this paper, digital image correlation (DIC) combined with ultra-high speed photography is utilized to study the loading rate effect of a granitic rock – Laurentian granite using notched semi-circular bend (NSCB) method. The dynamic stress intensity factors and crack tip positions are determined from the displacement fields obtained using DIC. Fracture time, fracture toughness and crack growth velocity all exhibit loading rate dependence. The dependence of fracture propagation toughness on crack growth velocity is also obtained, which is in good agreement with that reported in the literature.
Rare-earth-doped laser materials show strong prospects for quantum information storage and processing, as well as for biological imaging, due to their high-Q 4f↔4f optical transitions. However, the ...inability to optically detect single rare-earth dopants has prevented these materials from reaching their full potential. Here we detect a single photostable Pr(3+) ion in yttrium aluminium garnet nanocrystals with high contrast photon antibunching by using optical upconversion of the excited state population of the 4f↔4f optical transition into ultraviolet fluorescence. We also demonstrate on-demand creation of Pr(3+) ions in a bulk yttrium aluminium garnet crystal by patterned ion implantation. Finally, we show generation of local nanophotonic structures and cell death due to photochemical effects caused by upconverted ultraviolet fluorescence of praseodymium-doped yttrium aluminium garnet in the surrounding environment. Our study demonstrates versatile use of rare-earth atomic-size ultraviolet emitters for nanoengineering and biotechnological applications.
The molecular mechanism underlying gastric cancer (GC) invasion and metastasis is still poorly understood. In this study, we tried to investigate the roles of CXCR4 and CXCR2 signalings in gastric ...cancer metastasis. A highly invasive gastric cancer cell model was established. Chemokines receptors were profiled to search for the accountable ones. Then the underlying molecular mechanism was investigated using both in vitro and in vivo techniques, and the clinical relevance of CXCR4 and CXCR2 expression was studied in gastric cancer samples. CXCR4 and CXCR2 were highly expressed in a high invasive gastric cancer cell model and in gastric cancer tissues. Overexpression of CXCR4 and CXCR2 was associated with more advanced tumor stage and poorer survival for GC patients. CXCR4 and CXCR2 expression strongly correlated with each other in the way that CXCR2 expression changed accordingly with the activity of CXCR4 signaling and CXCR4 expression also changed in agreement with CXCR2 activity. Further studies demonstrated CXCR4 and CXCR2 can both activated NF-κB and STAT3 signaling, while NF-κBp65 can then transcriptionally activate CXCR4 and STAT3 can activate CXCR2 expression. This crosstalk between CXCR4 and CXCR2 contributed to EMT, migration and invasion of gastric cancer. Finally, Co-inhibition of CXCR4 and CXCR2 is more effective in reducing gastric cancer metastasis. Our results demonstrated that CXCR4 and CXCR2 cross-activate each other to promote the metastasis of gastric cancer.
Careful TEM examination has confirmed the formation of equiaxed α in nanocrystalline β during ageing of a severely deformed metastable β Ti alloy. It is revealed that the Burgers orientation ...relationship is obeyed upon α nucleation, but grain growth has led to the eventual incoherent α/β interfaces. In addition, intragranular acicular α would form when the β grains prior to ageing are much coarser than ~10nm.
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Naringinase was mainly obtained by microbial fermentation, and mutagenesis was a major way for obtaining excellent mutants. The aim of this study was to screen out a high naringinase yielding mutant ...to enhance the potential application value of its industrialization and compare the effects of different mutagenic methods on the enzyme activity of the strain. A novel producing naringinase strain, Aspergillus tubingensis MN589840, was isolated from mildewed pomelo peel, later subjected to mutagenesis including UV, ARTP and UV‐ARTP. After five rounds iterative mutagenesis, the mutants U1, A6 and UA13 were screened out with 1448·49, 1848·71, 2475·16 U mg−1 enzyme activity, the naringinase productivity raised by 79·08, 123·56 and 206%, respectively. In addition, the naringinase activity of three mutants rose after each round of iterative mutagenesis. These results indicated that the mutagenesis efficiency of UV‐ARTP was higher than that of single ARTP, and both are better than UV. In summary, the iterative UV‐ARTP mutagenesis is an effective strategy for screening high naringinase‐producing strains.
Significance and impact of the study: The ‘delayed bitterness’ of naringin in citrus processing is a challenging problem restricting the development of citrus processing industry. Naringinase can transform naringin to naringenin for debittering. Therefore, it is significant to breed high naringinase‐producing strains suitable for industrialization. In this study, we screened a naringinase high‐yielding mutant, which had potential industrial application value and laid a foundation for the development of citrus processing industry. In addition, the method of iterative UV‐ARTP mutagenesis provided an effective strategy for breeding high‐yield naringinase‐producing mutants.
Background
Understanding the dynamic tensile response of microwave damaged rock is of great significance to promote the development of microwave-assisted hard rock breakage technology. However, most ...of the current research on this issue is limited to static loading conditions, which is inconsistent with the dynamic stress circumstances encountered in real rock-breaking operations.
Objective
The objective of this work is to investigate the effects of microwave irradiation on the dynamic tensile strength, full-field displacement distribution and average fracture energy of a granitic rock.
Methods
The split Hopkinson pressure bar (SHPB) system combined with digital image correlation (DIC) technique is adopted to conduct the experiments. The overload phenomenon, which refers to the strength over-estimation phenomenon in the Brazilian test, is validated using the conventional strain gauge method. Based on the DIC analysis, a new approach for calculating the average fracture energy is proposed.
Results
Experimental results show that both the apparent and true tensile strengths increase with the loading rate while decreasing with the increase of the irradiation duration; and the true tensile strength after overload correction is lower than the apparent strength. Besides, the overload ratio and fracture energy also show the loading rate and irradiation duration dependency.
Conclusions
Our findings prove clearly that microwave irradiation significantly weakens the dynamic tensile properties of granitic rock.
High pressure torsion was conducted to obtain nano-sized β grains in a metastable Ti-5553 alloy. Much finer grains of <50nm were achieved, compared to >100nm in a stable Ti-20wt.% Mo alloy. The more ...effective grain refinement was attributed to stress induced martensitic transformation in the former, leading to the formation of thin α″ plates which divide β grains into smaller domains. Further deformation resulted in a reverse α″ to β transformation with decreasing α″ sizes, generating a completely nano β grain structure at very large straining. A detailed description of the β grain refinement mechanism is provided. The reverse transformation is shown to be caused by the significantly increased free energy below a critical α″ size of ∼10nm, consistent with experimental observations. It is also calculated that extremely high energies were required for the formation of α″ in nano-sized β grains, making further martensitic transformation impossible. It is concluded that the stress induced martensitic transformation and the subsequent reverse transformation are critical to producing nano-grained metastable β Ti alloys.
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