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In order to investigate the mechanical properties and failure mechanisms of the rock containing a single hole and double cracks, we used the 3D sand printing technique to prepare the rock-like specimens. Digital image correlation (DIC) method was employed to non-contactly monitor the deformation field of the specimens during the compression process. By calculating the convariance matrix of the horizontal, vertical and shear strains, we introduced the effective variance of the strain field to quantify and identify the failure behaviors of the specimens. The test results indicate that the mechanical properties of the standard 3D sand printed specimens are similar to those of natural sandstones, and the test data show a low dispersion. Therefore, they can be classified as a rock-like material. Due to the inclusion of the cracks, the mechanical properties of the specimens are degraded. The compressive strength and elastic modulus of the specimens each of which contains a single hole and double cracks are reduced by 8.04%-38.91% and 14.44%-27.78%, respectively, compared with those of the specimens each of which merely contains a single hole. Based on the DIC results, three basic types of cracks are identified successfully, i.e. tensile crack (Mode I), shear crack (Mode II) and mixed tensile-shear crack (Mode I-II). All the specimens each of which contains a single hole and double cracks show mixed tensile–shear failure (Mode I-II). The coalescence patterns between the hole and the cracks are influenced by their horizontal distance, and can be classified into tensile coalescence, rotation coalescence and mixed tensile-shear coalescence. The dispersion of the strain field can be quantified by the effective variance of strain field comprehensively. The effective variance of the strain field is close to zero at the initial crack closure stage and the elastic deformation stage. The cracks propagate in different manners after initiation. Based on the effective variance of the strain field, a quantitative method to identify the type of crack was proposed. The cracks can be identified as tensile crack, mixed tensile-shear crack, and shear crack, respectively, when the growth rates of the effective variance fall into the ranges of 0.72×10-2-1.89×10-2, 2.34×10-2-3.59×10-2, and 9.63×10-2-32.40×10-2, respectively.

Abstract Background MicroRNAs (miRNAs) are short, non-coding RNAs (~22 nt) that play important roles in the pathogenesis of human diseases by negatively regulating gene expression. Although miR-196a has been implicated in several other cancers, its role in non-small cell lung cancer (NSCLC) is unknown. The aim of the present study was to examine the expression pattern of miR-196a in NSCLC and its clinical significance, as well as its biological role in tumor progression. Methods Expression of miR-196a was analyzed in 34 NSCLC tissues and five NSCLC cell lines by quantitative reverse-transcription polymerase chain reaction (qRT-PCR). The effect of DNA methylation on miR-196a expression was investigated by 5-aza-2-deoxy-cytidine treatment and bisulfite sequencing. The effect of miR-196a on proliferation was evaluated by MTT and colony formation assays, and cell migration and invasion were evaluated by transwell assays. Analysis of target protein expression was determined by western blotting. Luciferase reporter plasmids were constructed to confirm the action of miR-196a on downstream target genes, including HOXA5. Differences between the results were tested for significance using Student’s t-test (two-tailed). Results miR-196a was highly expressed both in NSCLC samples and cell lines compared with their corresponding normal counterparts, and the expression of miR-196a may be affected by DNA demethylation. Higher expression of miR-196a in NSCLC tissues was associated with a higher clinical stage, and also correlated with NSCLC lymph-node metastasis. In vitro functional assays demonstrated that modulation of miR-196a expression affected NSCLC cell proliferation, migration and invasion. Our analysis showed that miR-196a suppressed the expression of HOXA5 both at the mRNA and protein levels, and luciferase assays confirmed that miR-196a directly bound to the 3’untranslated region of HOXA5. Knockdown of HOXA5 expression in A549 cells using RNAi was shown to promote NSCLC cell proliferation, migration and invasion. Finally, we observed an inverse correlation between HOXA5 and miR-196a expression in NSCLC tissues. Conclusions Our findings indicate that miR-196a is significantly up-regulated in NSCLC tissues, and regulates NSCLC cell proliferation, migration and invasion, partially via the down-regulation of HOXA5. Thus, miR-196a may represent a potential therapeutic target for NSCLC intervention.