Highlights • The average cross section shrinkage of the threads was about 30% less than that of the rebar. • Installation angle of rock bolt is a key factor to bolt end failure. • Thread suffers distinct stress concentrations in the valleys of the thread teeth. Abstract A comprehensive study including laboratory tests and numerical modeling was performed to investigate factors of rock bolt fracture. Experimental tests were performed to evaluate the mechanical performances of bolt ends including the thread and adjacent. The effects of installation angle, pretension and accessories (plate, washer and nut) were evaluated. It is found that a bolt installed with an oblique angle to roadway surface suffers a complex stress combination of tensioning, bending and twisting on the bolt. This complex stress is much greater than the tensile stress, leading to cracking and growth at the location of bending causing the thread to fail even though the tensile stress is less than the yield strength. Bolt thread is more vulnerable to fracture than rebar.

The digital divide has often been discussed with respect to the two opposite sides of the spectrum: the "haves" and "have-nots". However there is a gray area which consist of two particular categories: a) Internet users who did use the Internet at one time and have since stopped, or b) the large number of Internet users who stopped using the Internet but then restarted using it. Such Internet users have not received much academic attention. Studies of the digital divide would be incomplete without an analysis of these categories. This study has been a descriptive investigation of the populace that is neither a digital-have or nor a digital-have-not

BACKGROUND: Premature ovarian failure (POF) is a complex and heterogeneous disorder that is influenced by multiple genetic components. Here, we performed a two-stage association study to identify POF-associated genes. METHODS: A first stage linkage disequilibrium (LD)-based genome-wide association study was performed using 24 pairs of patients with POF and matched controls and a high-throughput BeadChip assay with 109365 single-nucleotide polymorphisms (SNPs) that are scattered throughout the genome in an exon-centric and evenly spaced manner. A region that was shown to be strongly associated with POF was then tested again for POF association in the second stage by using a larger sample size (101 cases and 87 controls) and additional putative causal SNPs. RESULTS: The first stage analysis revealed that many regions were associated with POF, with part of chromosome 7p14 that contains the parathyroid hormone responsive-B1 (PTHB1) gene showing the strongest association. A POF-susceptible haplotype of PTHB1 (ht1, 'GAAAG', P = 0.00034) and a POF-resistant haplotype (ht2, 'TGTGC') were also identified. The association between POF and two PTHB1 SNPs (rs3884597 and rs6944723) and part of ht1 was confirmed in the second stage analysis. The additional SNP, rs11773504, was considered as a putative causal variant causing an amino acid change, Ala to Thr. CONCLUSIONS: We showed for the first time that PTHB1 is strongly associated with POF, and ht1 confers susceptibility to POF. While causative SNPs were not identified, the polymorphism of the non-synonymous SNP rs11773504 and the repeated association of ht1 with POF suggest that PTHB1 may contribute to POF pathogenesis.

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